Microsoft Word - Phuong phap phan tich pho nguyen tu.doc

PHM LUNPHNG PHAP PHAN TICH PH NGUYN T(In Ln th 2 c sa cha v b sung)NH XUT BN I HC QUC GIA H NILI M UPhp o ph pht x v hp th nguyn t l nhng k thut phn tch ha l, v ang c pht trin v ng dng rng ri trong nhiu ngnh khoa hc k thut, trong sn xut cng nghip, nng nghip, y dc, a cht, ha hc. c bit cc nc pht trin, phng php phn tch ph pht x nguyn t tr thnh mt trong cc phng php dng phn tch lng vt cc kim loi trong nhiu i tng khc nhau nh t, nc, khng kh, thc phm, v.v... Hin nay trong cng tc nghin cu bo v mi trng, phng php phn tch ny l mt cng c c lc xc nh cc kim loi nng c hi. nc ta, k thut phn tch theo ph pht x v hp th nguyn t cng c pht trin v ng dng trong khong hn hai chc nm nay. Mt s phng th nghim c trang b my o ph pht x v hp th nguyn t, hoc do Nh nc ta u t, hoc do s vin tr ca cc t chc nc ngoi theo cc chng trnh khc nhau. Mt s cn b khoa hc ca ta c c ra nc ngoi hc tp, nghin cu v o to.Song iaskhng ciu kin,nhnglicn sdng k thut phn tchny cho cng vic phn tch ca h. Hu ht cc ti liu hay sch khoa hc v k thut ny li bng ting Anh. Mt khc, chng ta li cha c mt cun sch hoc cc ti liu c s l thuyt bng ting Vit v k thut phn tch ny.Do thc th , ng gp cho cng tc o to sinh vin trn lnh vc k thut phn tch ny ca Khoa Ha hc, Trng i hc Khoa hc T nhin - i hc Quc gia H Ni, cng nh to iu kin cho mt s cn b khoa hc, cng nhn vin phn tch ca cc phng th nghim khc c ti liu tham kho, chng ti mnh dn bin son cun sch ny. N c coi nh l gio trnh c s l thuyt v Phng php phn tch ph nguyn t. y cng l ni dung nhm phc v o to cao hc v k thut phn tch ny.y l gio trnh ting Vit u tin v k thut phn tch hin i ny nn khng th trnh khi nhng hn ch v thiu st nht nh. V th rt mong s ng gp thm kin ca cc bn b ng nghip v cc c gi quan tnm, tc gi c iu kin b sung cho hon chnh hn.Nhn dp ny chng ti xin chn thnh cm n GS. TS. J.F.M. Maessen, GS. TS. J. Kragton, GS. TS. Ban, TS. J.C. Kraak, cc k s H. Balker v J.W. Elgersma (khoa Ha, trng i hc tng hp Amsterdam, H Lan), GS. TSKH. Trnh Xun Gin (Vin Ha), TS. Nguyn Hong (HQGHN), PGS. TS. Phm Gia Hu (H Dc) v cc ng nghip B mn Ha Phn tch khoa Ha hc c nhiu kin ng gp cho ni dung ca gio trnh ny.Phm Lun2PHN IChng 1I CNG V PHNG PHP AES1.1 S phn loi phPhn tch quang ph l tn gi chung cho mt h cc phng php phn tch quang hc da trn c s ng dng nhng tnh cht quang hc ca nguyn t, Ion, phn t v nhm phn t. V d, tnh cht pht x hay hp th quang ca nguyn t, tinh cht hp th quang ca phn t, v.v... V vy ty theo quan nim, da theo nhng iu kin kch thch ph, phng tin thu ghi v quan st ph, cng nh bn cht ca qu trnh sinh ra ph m ngi ta c mt s cch phn chia thnh nhng php o khc nhau, nh php o ph pht x nguyn t, hp th nguyn t, php o ph hng ngoi,... Tuy th, nhng c hai cch phn chia sau y l ph hp hn:1.1.1 S phn chia theo c trng ca phTheo cch ny ngi ta c nhng phng php phn tch quang hc sau:Phng php phn tch ph nguyn t, gm c:a) Ph php x nguyn tb) Ph hp th nguyn tc) Ph hunh quang nguyn ty l ph do s chuyn mc nng lng ca cc in t ha tr ca nguyn t trng thi kh (hi) t do, khi b kch thch m sinh ra.Phng php phn tch ph phn t, gm c:a) Ph hp th phn t trong vng UV-VISb) Ph hng ngoi (IR v NIR)c) Ph tn x RamanPh ny c quyt nh bi cc in t ha tr ca nguyn t trong phn t, l nhng in t ha tr nm trong lin kt hay mt cp cn t do, chuyn mc nng lng khi b kch thch. Ph Rn-ghen (tia X), l ph ca in t ni ca nguyn t, gm c:+ Ph pht x tia X+ Ph hunh quang tia X+ Ph nhiu x tia X3 Ph cng hng t, gm:a) Cng hng t in t (ERMS).b) Cng hng t proton (ht nhn: NRMS)) Phng php phn tch khi ph: Ph ny c quyt nh bi khi lng ca cc Ion phn t hay cc mnh Ion ca cht phn tch b ct ra (t s m/z).y l cch phn chia c s dng rng ri v c coi nh l hp l nht v tng ng vi ngay tng php o c th..1.1.2 Phn chia theo di sngNh chng ta bit, bc x in t c mi bc sng, t sng di hng ngn mt n sng ngn vi micromet hay nanomet. Do ph ca bc x in t y phi cha ht tt c cc vng sng . Nhng trong thc t khng c mt dng c quang hc no c th c kh nng thu nhn, phn li hay pht hin c ton b vng ph nh th. V th ngi ta chia ph in t thnh nhiu min (vng ph) khc nhau. l nguyn tc ca cch chia th hai ny (bng 1.1).Bng 1.1S phn chia ph theo di sngSTTTn vng ph di sng

1Tia gama (y)< 0,1 nm

2Tia X0,1+ 5 nm

3T ngoi80 + 400 nm

4Kh kin400 + 800 nm

5Hng ngoi1+ 400 p,m

6Sng ngn400 + 1000 p,m

7Sng Raa0,1+ 1 cm

8Sng cc ngn0,1 - 50 cm

9Tivi - FM1 +10 m

10Sng raio10+ 1500m

Trong bng 1.1, vng ph t 3 n 5 l vng ph quang hc. Cc ph ny xut hin do s chuyn mc nng lng ca cc in t ha tr ca nguyn t v phn t, khi b kch thch. Vic phn chia theo cch ny cng c nhng im cha r rng, nh trong vng t ngoi v kh kin th c c ph ca nguyn t v phn t, m bn cht ca hai loi ph v s kch thch ca hai loi li rt khc nhau.4Trn y l hai cch phn chia chnh cn hay c dng. Tt nhin cn c mt s cch phn chia khc. Nhng c nhiu nhc im v t c s dng, nn khng cp n y.S phn chia ny c tnh cht gii thiu chung ton b vng ph. Song, trong gio trnh ny chng ti ch cp n ph pht x nguyn t, v phng php phn tch ng dng tnh cht pht x ca nguyn t trng thi hi c gi l K thut phn tch ph pht x nguyn t.1.2 S xut hin ph pht x nguyn t1.2.1 Tm tt v cu to nguyn tHng ngy chng ta thng quen vi nhng tn gi, st (Fe), ng (Cu) ch (Pb), bc (Ao), vng (Au), nhm (Aj), km (Zn),... l nhng nguyn t ha hc. n nay ngi ta bit trn 110 nguyn t ha hc khc nhau. Nhng v mt ha hc v theo thuyt ca alton, nguyn t ha hc bao gm nhng nguyn t ca cng mt loi v nguyn t l phn t nh nht cn gi c tnh cht ha hc ca nguyn t. Nguyn t ca mi nguyn t ha hc c cu to khc nhau nn chng c tnh cht khc nhau. Quyt nh tnh cht vt l v ha hc ca chng l cu to ca lp v electron trong nguyn t, c bit l cc in t ha tr.Nguyn t ca mi nguyn t ha hc u c xy dng t mt ht nhn nguyn t v cc electron (in t). Trong nguyn t, ht nhn gia, cc in t chuyn ng xung quanh ht nhn theo nhng qu o (orbital) tng i. Ht nhn chim th tch rt nh trong khng gian ca nguyn t (khong 1/10.000 th tch nguyn t), nhng li chim hu nh ton b khi lng ca nguyn t. Nu coi ng knh nguyn t l 10-8cm, th ng knh ht nhn ch chim khong 10-12cm. Nh vy,lpvcanguyntngoihtnhn lrtrng, n chnh l khng gianchuyn ng ca in t. S chuyn ng ca in t trong khng gian ny rt phc tp. N va tun theo quy lut ca chuyn ng sng, li va tun theo quy lut chuyn ng ca cc ht vi m. Song trong mt iu kin nht nh v mt cch tng i, ngi ta vn tha nhn cc in t chuyn ng trong khng gian ca nguyn t theo ccqu o. Nhng theo quanimhini cac lngtth l ccmmy electron.Trong lp v nguynt,intphnbthnhtnglpngvislngtchnh ca nguyn t (n). Trong tng lp li c nhiu qu o ng vi s lng t ph 1 ca nguyn t. l cc phn lp. Nhng theo nguyn l vng bn th in t bao gi cng chim v lm y nhng qu o c mc nng lng thp trc. Sau mi n nhng qu o c mc nng lng cao hn. Th t sp xp l: ls, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, v.v... (hnh 1.1a).5

Hnh 1.1aS phn b nng lng trong nguyn t(1)-cu to nguyn t: (2)-phn b nng lng trong lp v nguyn t.6

Qu trnh pht x v hp th ca mt nguyn t.E0: Nng lng trng thi c bn; cm: Nng lng trng thi kch thch; + hv v + AE: Nng lng kch thch; - hv: Tia pht x.(n = 5) (n = 4)(n = 3)(n = 2)Hnh 1.1 bS phn b nng lng trong nguyn t v sinh ph1.2.2 S xut hin ph pht xTrong iu kin bnh thng, cc in t chuyn ng trn cc qu o ng vi mc nng lng thp nht. Khi nguyn t trng thi bn vng, trng thi c bn. trng thi ny nguyn t khng thu v cng khng pht nng lng. Nhng nu cungcp nng lng cho nguyn t th trng thi khng tn ti na. Theo quan im ca thuyt lng t, khi trng thi kh, in t chuyn ng trong khng gian ca nguyn t, c bit l cc in t ha tr, nu chng nhn c nng lng bn

7ngoi (in nng, nhit nng, ha nng,...) th in t s chuyn ln mc nng lng cao hn. Khi nguyn t b kch thch. N tn ti trng thi kch thch. Nhng trng thi ny khng bn vng. Nguyn t ch lu li trng thi ny nhiu nht l 10 8 giy. Sau n lun lun c xu hng tr v trng thi c bn ban u bn vng. Ngha l gii phng nng lng m chng hp th c trong qu trnh trn di dng ca cc bc x quang hc. Bc x ny chnh l ph pht x ca nguyn t, n c tn s c tnh theo cng thc:AE = (En - Eo) = hv(1.1)hay: AE = Xtrong :En v E0 l nng lng ca nguyn t trng thi c bn v trng thi kch thch n;h l hng s Plank (6,626.10-7 erk.s) hay h = 4,1.10-15 eV.s;c l tc nh sng (3.108 m/gy) - 2,99793.108 m/gy;v l tn s ca bc x ;X l bc sng ca bc x .Trong biu thc trn, nu gi tr AE l nm ta c qu trnh hp th v khi gi tr AE dng ta c qu trnh pht x ca nguyn t.Nhng trong nguyn t, s chuyn mc ca in t t mc nng lng En khng phi ch v mc E0, m c rt nhiu s chuyn mc t En v cc mc khc E01, E02, E03_ cng vi mc E0. Ngha l c rt nhiu s chuyn mc ca in t c lng t ha, v ng vi mi bc chuyn mc ta c 1 tia bc x, tc l mt vch ph. Chnh v th m mt nguyn t khi b kch thch thng c th pht ra rt nhiu vch ph pht x. Nguyn t no c nhiu in t v c cu to phc tp ca cc lp in t ha tr th cng c nhiu vch ph pht x. Mt cch tng trng ta c th m t qu trnh kch thch v pht x ca nguyn t theo m hnh trong hnh 1.2.Nu dng my quang ph thu chm ra pht x , phn li v ghi li cc chm tia pht x do nguyn t pht ra ta s c mt di ph t sng ngn n sng di. l ph pht x ca nguyn t ca cc nguyn t v n l ph vch. Nh vy, ph pht x nguyn t l sn phm sinh ra do s tng tc vt cht, m y l cc nguyn t t do trng thi khvimt ngunnnglngnhit,in... nhtnhph hp.Nhng trong ngun sng, khng phi ch c nguyn t t do b kch thch, m c c Ion, phn t, nhm phn t. Cc phn t ny cng b kch thch v pht ra ph pht x ca n. Tt nhin l trong mc khc nhau ty thuc vo kh nng kch thch ca ngun nng lng. V vy, ph pht x ca vt mu lun bao gm ba thnh phn:1. Nhm ph vch. l ph ca nguyn t v con. Nhm ph vch ny ca cc nguyn t ha hc hu nh thng nm trong vng ph t 190-1000nm (vng UV- VIS). Ch c mt vi nguyn t kim hay kim loi kim mi c mt s vch ph nm ngoi vng ny.2. Nhm ph m. l ph pht x ca cc phn t v nhm phn t. V d8ph ca phn t MeO, CO v nhm phn t CN. Cc m ph ny xut hin thng c mt u m v mt u nht. u m pha sng di v nht pha sng ngn. Trong vng t ngoi th ph ny xut hin rt yu v nhiu khi khng thy. Nhng trong vng kh kin th xut hin rt m, v lm kh khn cho php phn tch quang ph v nhiu vch phn tch ca cc nguyn t khc b cc m ph ny che lp.3. Ph nn lin tc. y l ph ca vt rn b t nng pht ra, ph ca nh sng trng v ph do s bc x ring ca in t. Ph ny to thnh mt nn m lin tc trn ton di ph ca mu. Nhng nht sng ngn v m dn v pha sng di. Ph ny nu qu m th cng s cn tr php phn tch.Ba loi ph trn xut hin ng thi khi kch thch mu phn tch v trong phn tch quang ph pht x nguyn t ngi ta phi tm cch loi bt ph m v ph nn. l hai yu t nhiu.1.3 Nguyn tc ca php o ph pht x (AES)T vic nghin cu nguyn nhn xut hin ph pht x, chng ta c th khi qut phng php phn tch da trn c s o ph pht x ca nguyn t phi bao gm cc bc nh sau:1. Trc ht mu phn tch cn c chuyn thnh hi (kh) ca nguyn t hay Ion t do trong mi trng kch thch. l qu trnh ha hi v nguyn t ha mu. Sau dng ngun nng lng ph hp kch thch m hi chng pht x. y l qu trnh kch thch ph ca mu.2. Thu, phn 1i v ghi ton b ph pht x ca vt mu nh my quang ph. Trc y, ph c ghi ln knh nh hay phim nh. Chnh my quang ph s lm nhim v ny. Nhng nhng trang b hin i ngy nay c th thu v ghi trc tip cc tn hiu cng pht x ca mt vch ph di dng cc lc trn bng giy hay ch ra cc sng cng vch ph trn my in (printer), ghi li vo a t ca my tnh.3. nh gi ph ghi v mt nh tnh v nh lng theo nhng yu cu t ra. y l cng vic cui cng ca php o.Chnh v vy, ng vi cc nhim v v nguyn tc ny, thc hin mt php phn tch da theo ph pht x ca nguyn t ngi ta phi cn mt h thng trang b cng gm ba phn tng ng nh th.A. Trang b c bn (ti thiu phi c): Phn 1: Ngun nng lng ha hi, nguyn t ha mu v kch thch ph ca mu phn tch, c ph ca nguyn t phn tch. Phn 2: My quang ph thu, phn li v ghi li ph pht x ca mu phn tch theo vng ph ta mong mun. Phn 3: H thng trang b nh gi nh tnh, nh lng v ch th hay biu th cc kt qu.Mt cch tng qut, ta c th m t nguyn tc ny theo s hnh 1.3.9

Ion Mg+Singlet Triplet

B. Trang b hon chnh:C thm cc b phn sau:1. B t ng bm hay a mu vo o.11Hnh 1.2bS vch ph pht x ca nguyn t Mg2. H my tnh v phn mm ca n.

Mu phn tchHa hi, nguyn t ha v kch thch ph pht x(AES)Thu, phn li, ghi bc xNgun ENgn la H quang Tia in ICP-plasma(theo ba cch khc nhau)Cch ICch IIQuan st trc tip nh tnh v nh lng (Spectroscop)nh gi nh tnh v bn nh lng (Spectroprojector)Ghi ph ln knh nh (Spectrograph)

Knh nh cha ph mu p.t.

nh gi nh tnh, nh lng (theo hai cch)

r

o en trc tip bng vi quang kMy t ghi I ca vch ln bng giy

Cch IIIThu, phn li, ghi trc tip ph mu p.t. (Spectrometer, mt hay nhiu knh)Chn, khuch i tn hiu, b chnh My tnh (Microcomputer) x l kt quHin s" kt quIn kt quT ghi cng Hnh 1.3S nguyn l ca qu trnh phn tch AES12

Hnh 1.4Vng nng phn tch ca cc phng php ph13Nng 1.4 i tng ca phng php phn tch ph pht xBn cnh mc ch nghin cu vt l quang ph nguyn t, php o ph pht x nguyn t l mt phng php phn tch vt l da trn tnh cht pht x ca nguyn t trng thi hi xc nh thnh phn ha hc ca cc nguyn t, cc cht trong mu phn tch. V vy n c tn phn tch quang ph ha hc. Phng php ny c s dng phn tch nh tnh v nh lng cc nguyn t ha hc, ch yu l cc kim loi trong mi i tng mu khc nhau, nh a cht, ha hc, luyn kim, ha du, nng nghip, thc phm, y dc, mi trng... thuc cc loi mu rn, mu dung dch, mu bt, mu qung, mu kh. Tuy phn tch nhiu i tng, nhng thc cht l xc nh cc kim loi l chnh, ngha l cc nguyn t c ph pht x nhy, khi c kch thch bng mt ngun nng lng thch hp; sau l mt vi kim nh Si, P, C. V vy, i tng chnh ca phng php phn tch da theo php o ph pht x ca nguyn t l cc kim loi nng nh trong cc loi mu khc nhau. Vi i tng kim th phng php ny c nhiu nhc im v hn ch v nhy, cng nh nhng trang b thu, ghi ph ca chng, v ph ca hu ht cc kim li nm ngoi vng t ngoi v kh kin, ngha l phi c thm nhng trang b phc tp mi c th phn tch c cc kim.1.5 Cc u im v nhc imPhng php phn tch quang ph pht x nguyn t s d c pht trin rt nhanh v c s dng trong nhiu lnh vc ca khoa hc, k thut cng nghip, nng nghip v i sng v n c nhng u im rt c bn:a) Phng php ny c nhy rt cao. Bng phng php ny nhiu nguyn t c th c xc nh t n nhy t n.103 n n.104 %. Nhng vi nhng trang b hin i v vi nhng ngun kch thch ph mi (ICP) ngi ta c th t n nhy t n.10-5 n n.10-6 % i. Vi nhiu nguyn t m khng cn phi lm giu mu phn tch (bng 1). V th n l phng php kim tra, nh gi tinh khit ca nhiu ha cht v nguyn liu tinh khit cao, phn tch lng vt cc kim loi nng c hi trong i tng thc phm, nc gii kht, mi trng. Trong khi vi nhng i tng ny th phng php ha hc khng th no t c.b) Phng php ny gip chng ta c th tin hnh phn tchngthinhiunguyn t trong mt mu, m khng cn tch ring chng ra khi nhau. Mt khc, li khng tn nhiu thi gian, c bit l phn tch nh tnh v bn nh lng.c) Vi nhng tin b ca k thut hin nay v vi nhng trang b hin nay t c, th phng php phn tch theo ph pht x nguyn t l mt php o chnh xc tng i cao. Trong nhiu trng hp, vi nng nh (c ppm) m sai s ca php o l di 10%. Tt nhin vi nhng trang b v my mc c in thsaiscth lnhn. Song thc t n b nhng trang b hin i y li.14d) Phng php phn tch theo ph pht x l mt phng php phn tch tiu tn t mu, ch cn t 1 n vi chc miligam mu l . c bit l k thut ph pht x.e) Phng php phn tch ny c th kim tra c ng nht v thnh phn ca vt mu nhng v tr (ch) khc nhau. V th cng c ng dng kim tra ng nht ca b mt vt liu.f) Trong nhiu trng hp, ph ca mu nghin cu thng c ghi li trn phim nh, knh nh hay trn bng giy. N l nhng ti liu lu tr v khi cn thit c th nh gi hay xem xt li m khng cn phi c mu phn tch.Bn cnh nhng u im nu, phng php ny cng c mt s nhc im v hn ch nht nh. Trc ht phi ni n l: Phng php ny ch cho chng ta bit c thnh phn nguyn t ca mu phn tch, m khng ch ra c trng thi lin kt ca n trong mu. chnh xc ca php phn tch ph thuc vo nng chnh xc ca thnh phn ca dy mu u v cc kt qu nh lng u phi da theo cc ng chun ca cc dy mu u c ch to sn trc.Mc du c mt s nhc im v hn ch, nhng phng php phn tch quang ph pht x nguyn t ngy cng c pht trin v ng dng rng ri trong nhiu lnh vc khc nhau xc nh lng vt cc nguyn t trong cc i tng mu khc nhau. l mt phng php phn tch nhanh, c chnh xc bo m v nhy kh cao, c bit thch hp cho phn tch t him, cc loi nc, khng kh, v.v.1.6 Kh nng v phm vi ng dngPhng php phn tch quang ph pht x nguyn t ngy nay gi vai tr quan trng trong ha hc phn tch. Cng vi s pht trin mnh m ca cc ngnh khoa hc k thut, c bit l vt l v ha hc, s pht trin ca k thut o v ghi tn hiu, lm tng kh nng ng dng to ln ca n. Bng phng php ny ngi ta c th xc nh nh tnh, bn nh lng v nh lng c hn nm chc kim loi v gn mt chc nguyn t kim trong cc i tng mu khc nhau (v c v hu c). Phng php phn tch ny tr thnh cng c phn tch nguyn t c lc ch nhiu lnh vc, nht l sau khi c ngun kch thch ICP.a) Phn tch quang ph pht x trong ngnh ha v cng nghip ha hc. N l cng c cc nh ha hc xc nh thnh phn nh tnh v nh lng ca nhiu cht, kim tra tinh khit ca cc ha phm, nguyn liu v nh gi cht lng ca chng. N cng l mt phng php xc nh cc ng v phng x v nghin cu cu trc nguyn t.b) Phn tch quang ph pht x nguyn t trong a cht. Ngay t khi mi ra i, phng php ny c cc nh a cht s dng phn tch cc mu qung phc v cho cng vic thm d a cht v tm ti nguyn khong sn. V th ngnh a cht ca tt c cc nc u c phng phn tch quang ph pht x rt hin i v hon chnh.15c) Phn tch quang ph pht x trong luyn kim. Luyn kim cng l mt ngnh s dng phng php phn tch quang ph pht x u tin vo mc ch ca mnh trc c ngnh ha. Chnh tnh cht nhanh chng v nhy ca phng php ny l mt iu rt cn thit i vi ngnh luyn kim. N c th l cng c gip cc nh luyn kim xc nh ngay c thnh phn ca cc cht ang nng chy trong l luyn kim; qua m h c th iu chnh nguyn liu a vo ch to c nhng hp kim c thnh phn mong mun, kim tra thnh phn, kim tra nguyn liu.d) Phn tch quang ph pht x trong tiu ch un hc. Trc y con ngi tng rng kh c th hiu bit c thnh phn ha hc ca cc hnh tinh xung quanh tri t chng ta. Nhng phng php phn tch quang ph pht x ra i m rng tm vi cho con ngi. Bng phng php ph pht x v kt hp vi mt s knh thin vn, cc nh thin vn c th quan st c thnh phn ca cc nguyn t ha hc ca cc hnh tinh khc nh mt trng, cc v sao. Chnh nhng kt qu phn tch thnh phn ca cc mu t do v tinh ly t mt trng v ni ln ngha ca php o ph pht x trong lnh vc nghin cu thin vn. V nhng kt qu phn tch thc t cc mu l rt ph hp vi nhng s liu thu c trc y qua phn tch tia sng t mt trng bng h thng my quang ph v knh thin vn.e) Phn tch quang ph pht x trong nng nghip, y v sinh hc. y l nhng ngnh khoa hc s dng phng php ny cm li nhiu kt qu rc r, c bit l trong vic nghin cu th nhng, nghin cu cc nguyn t vi lng trong t trng, trong cy trng, trong phn bn ca nng nghip, hay nghin cu thnh phn thc n phc v chn nui, phn tch nguyn t vi lng trong mu, serum, nc tiu, phc v cha bnh.f) Phn tch quang ph trong cc lnh vc khc. Ngoi nhng lnh vc nu, phng php phn tch quang ph pht x nguyn t cn c mt s ngnh khc s dng nh l mt cng c phn tch. V d nh trong ngnh dc kim tra mt s kim loi c hi trong cc dc phm (Pb, Cu, Zn, Hg,...). Ngnh nghin cu c s, cng an, to n, ngoi thng, cng l nhng ni s dng phng php phn tch quang ph trong cc lnh vc nghin cu v nng php o ph nguyn t ln ngang tm ca thi i.Hnh 1.5S phn chia cc loi ph theo di sng16Chng 2S KCH THCH PH PHT X NGUYN TYu cu v nhim v ca ngun kch thchTrong phn tch quang ph pht x nguyn t, ngun sng c gi l ngun kch thch ph v c mt vai tr ht sc quan trng. V nh ngun nng lng kch thch ngi ta c th chuyn vt liu mu phn tch thnh trng thi hi ca cc nguyn t v kch thch m hi pht sng (pht x), ngha l ngun nng lng nh hng trc tip n kt qu ca php phn tch. V vy ngun nng lng mun dng c vo mc ch phn tch quang ph pht x nguyn t cn phi thc hin c hai nhim v sau y:Trc ht ngun nng lng phi ha hi, nguyn t ha v chuyn c hon ton cc nguyn liu mu phn tch vo vng phng in (plasma). C nh th thnh phn ca m hi trong plasma mi ng nht vi thnh phn ca vt mu. ng thi ngun nng lng phi c nng lng ln (nhit ) c th kch thch c tt nht cc nguyn t ca nguyn t cn phn tch i n pht x ra ph ca n.Song nh th vn cha hon ton . V mt phng php phn tch ch c gi tr khi n c nhy v lp li cao. Chnh v th, ngoi hai nhim v trn mt ngun sng mun dng c lm ngun kch thch ph pht x n cn cn phi tha mn mt s yu cu nht nh sau y:Trc ht ngun sng phi m bo cho php phn tch c nhy cao v cng ca vch ph phi nhy vi s bin thin nng ca nguyn t phn tch; nhng li khng nhy vi s dao ng ca iu kin lm vic.Ngun nng lng phi n nh v bn vng theo thi gian, m bo cho phng php phn tch c lp li v n nh cao. Ngha l cc thng s ca ngun sng chn nht thit phi duy tr v lp li c.Ngun nng lng phi khng a thm ph ph vo lm ln vi ph ca mu nghin cu. Nu khng s lm kh khn thm cng vic nh gi nh tnh v nh lng v c khi lm sai lc c kt qu phn tch.Ngun kch thch phi c s cu to khng qu phc tp; nhng li c kh nng thay i c nhiu thng s, c th chn c nhng iu kin ph hp theo tng i tng phn tch hay tng nguyn t.Yu cu cui cng l ngun nng lng kch thch phi lm tiu hao t mu phn tch v trong mt s trng hp phi khng lm h hi mu phn tch, nh trong17kim tra thnh phm.Trn y l nhng yu cu chung, nu ngun sng tha mn c y cc yu cu l mt iu rt l tng. Song trong thc t khng c c iu kin l tng nh th. V vy, mi ngi lm phn tch quang ph pht x cn phi hiu bit tng tn v ty theo tng trng hp c th m xem yu cu no cn c ch nghim ngt trc ht v yu cu no c th chnm chc c.Cc loi ngun kch thch ph pht xDo nhng yu cu nu trn, nn ch c mt vi loi ngun nng lng c dng lm ngun kch thch cho phng php phn tch quang ph pht x. l: Ngn la n kh; H quang in dng xoay chiu v mt chiu; Tia la in; Tia lc; Plasma cao tn cm ng (ICP); tia X.Trong cc loi ngun nng lng ny, ngn la n kh, h quang v tia la in c dng t lu, nhng c nhy khng cao (ngun sng c in). Tia lc v ICP l nhng ngun nng lng cho nhy cao. Nhng tia lc t c dng. V c c tia lc ph hp cho mc ch phn tch phi c nhng trang b phc tp, tn km. Ring ICP l ngun nng lng hin ang c ng dng ph bin v c nhiu u vit. N l ngun sng mi c pht trin trong vng hn chc nm li y. Li khng t nh ngun lc. V nhy ca cc ngun nng lng ny chng ta c th xem trong hnh 1.4 v bng ph lc A.Ngn la n khCu to v c im ngn la n khNgn la n kh l ngun nng lng u tin c dng trong phn tch quang ph pht x nguyn t, ngay t khi phng php ny ra i. Bunsen v Kirschoff l nhng ngi u tin dng ngun sng ny phn tch cc kim loi kim v kim th. Nhng do s n gin, n nh, nhy tng i v r tin, nn ngy nay n vn c s dng ph bin.c im. Ngn la n kh c nhit khng cao (1700 - 32000C), c cu to n gin, nhng n nh v d lp li c cc iu kin lm vic. Do c nhit thp, nn ngn la n kh ch kch thch c cc kim loi kim v kim th. V ng vi loi ngun sng ny ngi ta c mt phng php phn tch ring. l phng php phn tch quang ph ngn la (Flame Spectrophotometry). Song v bn cht n vn l ph pht x ca nguyn t trong ngn la. Cc cht kh t to ra ngn la ca n kh thng l mt hn hp ca hai kh (1 kh oxy ha v 1 kh nhin liu) c trn vi nhau theo mt t l nht nh. Bn cht v thnh phn ca hn hp kh quyt nh nhit ca ngn la v hnh dng cu to ca ngn la. Di y l mt vi hn hp kh c s dng to ra ngn la trong php o ph pht x:18Bng 2.1Nhit ca mt s loi n khSTTLoi hn hp kh tNhit (oC)

1Axetylen v oxy2400-3100

2Butan v oxy2000-2550

3Kh t v oxy2200-2500

4Hydro v oxy2100-2300

5Axetylen v khng kh2000-2450

Cu to. V hnh dng cu to v s phn b nhit ca ngn la, n kh gm ba phn nh sau (hnh 2.3 v 2.4): Phn mt (a). Phn trong cng st ming n l phn ti (a). Trong phn nycht t c trn v nung nng chun b t chy phn hai (b). Nhit trongphn ny thp (di 700-12000C). Phn hai (b) l li ca ngn la.Trong phn ny xy ra cc phn ng t chycht kh. N khng mu hay c mu xanhnht v nhit l cao nht. Chnh nh b lch c nhit cao nht ca ngn la. Nut bng hn hp kh axtylen v oxy haykhng kh nn th nhit ca ngn la ccung cp nh phn ng:2C2H2 + 2O2 = 4CO + 2H2 + Q Phn th ba (c) l v ca ngn la.Trong phn ny thng xy ra cc phn ngth cp, c mu vng v nhit thp. N tothnh ui v v ca ngn la.Do s phn b nhit ca ngn la nh vy, nn kh phn tch phi a mu vo vng tnm c nhit cao nht. l vng b ca ngn la v trong vng ny cc qu trnh s n nh, v hiu sut kch thch ph s cao nht.

19n nguyn t ho mu (burner head)L b phn t chy hn hp khto ra ngn la. Tuy c nhiu kiu n khcnhau, nhng u c nguyn tc cu toging nhau (hnh 2.4 v 2.5). l h thngnguyn t ha mu. Song bt k mt loin no mun dng c cho php phntch quang ph, ngoi nhng yu cu nu(mc 1) n cn phi m bo trn u hnhp kh trc khi t v ngn la phi chy ngoi ming n.n v h thng NTH mu ca hngHnh 2.4.

Philips(1) n nguyn t ha mu; (2) Mng bo him; (3) ng thi phn mu tha; (4) ng dn cht oxy ha; (S) ng dn mu vo bung aerosol ha; (6) ng dn cht chy C2H2; (7) Vin bi to bi aersol.H nguyn t ha mu bao gm:+ Bung ht mu v to th si kh (1)+ n nguyn t ha mu (2)H thng nbiulai theo k thut pneumaticK: Kh mang (oxy ha); S: ng dn mu; F: Kh chy; Q: Cnh qut quay u; G: Mng bo him; A: ng dn th aetosol ln n nguyn t ha.Qu trnh kch thch ph trong ngn laTrong phn tch quang ph pht x, nu dng ngn la lm ngun kch thch th mu phn tch phi chun b dng dung dch. Sau nh mt h thng phun(2)

AHnh 2.520(Nebulizer system) a dung dch ny vo ngn la di dng th sng m (th si kh - aersol) cng vi hn hp kh t. Khi vo ngn la, di tc dng ca nhit , trc ht dung mi bay hi, li cc ht bt mu mn ca cc cht phn tch, ri n c t nng v chuyn thnh hi ca nguyn t v phn t. Trong ngn la cc phn t hi ny chuyn ng, va chm vo nhau, trao i nng lng cho nhau,... Kt qu ca cc qu trnh lm cc phn t b phn li thnh nguyn t, b Ion ha v b kch thch. Nh vy trong ngn la tn ti c nguyn t t do, phn t, Ion, nhm phn t v cc in t. Trong tp hp ch yu ch cc nguyn t t do b kch thch v pht x. V th ph pht x ngn la l ph ca nguyn t trung ha. Nguyn nhn gy ra s kch thch ph y l s va chm ca cc nguyn t vi cc in t c ng nng ln trong ngn la. V th nhit ngn la cng cao th cc in t c ng nng cng ln. V th n l s kch thch nhit. Do c ch ca qu trnh kch thch trong ngn la l:Trc ht l dung mi bay hi, li cc ht mu dng bt. Tip theo l bt mu b nung nng, nng chy. Sau l cc qu trnh nhit ha ca cht mu xy ra theo tnh cht ca n, v gm c.Hai qu trnh chnh: NuEh< Ent thmusha hi, nguyn t ha tora cc nguynttdo,chng b kch thch v pht x ^ c ph pht x (AES).Men Xm(r).Th. ^ Men Xm(k) ^ mMe(k) + nX(k)Me(k) + E ^ Me(k)* ^ Me O + n(Hv)Nng lng K Chm tia pht xC ch ny (c ch 1) cho nhy v n nh cao ca s pht x. Cc hp cht mui halogen (tr F), axetat, mt s nitrat, sunphat... ca kim loi thng theo c ch ny. Nu Eh > Ent th mu s b nguyn t ha trc, sau ha hi thnh nguyn t, ri b kch thch ph ^ sinh ra ph pht x (AES).MenXm(r) ^ Mn(r) + Xm(r) ^ mMe(k) + nX(k)Me(k) + E ^ Me(k)* ^ Me O + n(Hv)Nng lng K.Th. Chm tia pht xC ch ny (c ch 2) cho nhy v n nh km so vi c ch 1 ca s pht x.Cc hp cht mui SIO2-3, PO3-4, F", mt s nitrat, sunphat,.. ca kim loi thng theo c ch ny.Do c im ca 2 c ch chnh , nn trong phn tch ngi ta thng to iu21kin s kch thch ph xy ra theo c ch 1 c li. iu gii thch ti sao ngi ta hay dng cc mui halogen, v axetat ca kim loi kim lm nn, hay cht ph gia cho mu phn tch.Qu trnh phTrong ngn la thng c cc qu trnh ph km theo hai qu trnh chnh, cc qu trnh ny ty iu kin ca ngn la m xut hin trong mc khc nhau, v n u khng c li, nn cn c loi tr trong phn tch. Cc qu trnh l:To ra cc hp cht bn nhit, ch yu l cc monoxit (dng MeO).S Ion ha to ra cc Ion, ch yu l s Ion ha bc 1.S hp th bc x ca nguyn t (qu trnh t o).S pht x ph nn lin tc ca ht rn v electron b nung nng.Ni chung, cc qu trnh ny u khng c li. Ngi ta phi tm bin php loi tr. V d:+ hn ch s hnh thnh hp cht bn nhit kiu MeO, ngi ta thm vo mu mui Clorua ca kim loi kim (nh KCI, CsCL) lm nn, kch thch ph theo c chhoc kch thch ph trong mi trng kh tr argon.+ Hay loi tr s Ion ha ca nguyn t phn tch, ngi ta thm vo mu cht ph gia l mui halogen kim loi kim c th Ion ha thp hn th Ion ha ca nguyn t phn tch. Nh th nguyn t phn tch s khng b Ion ha na.So vi cc loi ngun kch thch khc, ngn la l ngun kch thch n gin, nhy trung bnh (0,1 - 10p,g) v tng i n nh. Nhng cng ca vch ph cng b nh hng bi mt s yu t nht nh, nh:+ Trc ht l dng lin kt ca cc nguyn t trong cht mu.+ Th hai l nh hng ca cc gc axit. Ni chung, cc axit d bay hi th nh hng ny l nh.+ Th ba l cht nn hay thnh phn ca dung dch mu, v vy dung dch phn tch v dung dch mu chun u phi c cng thnh phn vt l v ha hc, nht l cht nn phi cng loi.+ nh hng th t l cc phn ng ha hc xy ra trong ngn la. c bit l nh hng ca cc phn ng to ra cc hp cht bn nhit. Cc hp cht ny thng lm gim cng ca vch ph, ngha l lm gim nhy ca phng php phn tch. l khi qut chung, tt nhin cc yu t trn khng phi bao gi cng xut hin ng thi v tc dng nh nhau trong mi trng hp, m ty tng trng hp yu t no l ni bt v cn c ch . Song mt iu cn nh l nhit ngn la l yu t quan trng nht, n quyt nh cc qu trnh xy ra trong khi kch thch ph.22H quang inc im v tnh chtH quang l ngun kch thch c nng lng trung bnh v cng l ngun kch thch vn nng. N c kh nng kch thch c c mu dn in v khng dn in. Ty thuc vo cc thng s (A, C, R) ca my pht h quang v loi in cc ta chn m h quang c nhit t 3 5 00 - 60 000C Vi nhit ny nhiu nguyn t t cc nguyn liu mu khc nhau c th c ha hi, nguyn t ha v kch thch ph pht x. Nhit ca h quang ph thuc rt nhiu vo bn cht ca nguyn liu lm in cc. V th trong mt iu kin nh nhau, h quang in cc than (graphite) c nhit cao nht (bng 2.2). Cng dng in trong mch h quang l yu t quyt nh nhit ca h quang.H quang l ngun kch thch cho nhy tng i cao, v trong h quang mu phn tch c ha hi tng i d dng hn trong cc loi ngun nng lng khc, c bit l h quang dng mt chiu. Nhng cng do tnh cht ny m php phn tch dng h quang c n nh v lp li km ngn la v tia in. y h quang dng xoay chiu cho kt qu n nh hn h quang dng mt chiu, v th h quang dng xoay chiu c s dng nhiu hn.Bng 2.2Th Ion ha v nhit h quang ca mt s kim loiNguyn t lm in ccTh Ion ha ca nguyn t (eV)Dng in h quang (A)Nhit ca h quang (oC)

C11,30106000

Zn9,40105200

Fe7,80104800

Cr6,90104400

Al5,67104000

H quang l ngun kch thch c s mch tng i n gin, nhng li c nhiu thng s c th iu chnh c chn c mt nhit tng i ph hp cho php phn tch mi cht.H quang l s phng in gia hai in cc c th thp (di 260V) v dng cao (t 8 - 20A). Th v dng ca mch h quang c lin h vi nhau theo cng thc:, B_UU _ A + v I _ Imm R + R2Trong A v B l cc hng s, Ri l in tr plasma h quang. Cng thc ny gii thch ti sao h quang km bn vng. V th phi a vo mch h quang mt23bin tr ph R2 tht ln (R2 >> Ri) hn ch s thay i cng dng in trong mch v gi cho h quang n nh.Cu to v hot ng ca h quangTuy c nhiu loi my pht h quang khc nhau, nhng v nguyn tc cu to, tt c cc my pht h quang u gm hai phn chnh.Phn 1 l mch pht h quang (mch chnh), n c nhim v cung cp nng lng ha hi, nguyn t ha mu v kch thch m hi i n pht x. Nu h quang mt chiu th l mch ca dng in mt chiu (hnh 2.6). Nu l h quang xoay chiu, th l dng in xoay chiu.Phn 2 l mch ch huy (mch iu khin), c nhim v ch huy phn mch chnh hot ng theo nhng thng s c chn cho mt mc ch phn tch nht nh. Theo s hnh 2.6, nu cng tc K c ng v tr AA, ta c h quang dng xoay chiu. Cn khi v tr BB' ta c h quang dng mt chiu. S hot ng ca h quang din ra nh s (s hnh 2.6):Khi ng cng tc K', ngha l a in vo my, qua h thng bin tr R; ta chn c th lm vic ph hp a vo bin th Tr1 tng th. Khi th hai u cun th cp ca bin th ny t n hng ngn vn (2000-7000V). Hai u cun ny c ni vi cun cm Li, t in C1 v khong n ph E. Lc t C1 c tch in v khi t n th Vf chn th c mt tia in c nh qua khong E, nh th lp tc trn mch dao ng L1c1 xut hin mt dao ng cao tn. Do mch dao ng L2C2 cng ghp vi mch dao ng LlC1, nn trn mch L2C2 cng xut hin mt dao ng cao tn cm ng nh th. Nhng s vng ca L2 l ln hn nhiu L1s nn th trn hai ct ca t C2 cng s ln hn C1. Th ny li xut hin tc khc khi c tia in nh E v iu khin s phng in qua khong F ca hai in cc h quang. Nh th mt chu k phng in th nht c thc hin v kt thc, ri li tip din n chu k phng in th hai, th ba,... v c th din ra cho n khi no ta ngt cng tc K', tc l ngng s phng in ca h quang.

Hnh 2.6S nguyn tc cu to ca my pht h quang24Khi h quang lm vic, in cc F s c t nng v di tc dng ca in trng cc in t bt ra khi b mt in cc nm, chng c gia tc v chuyn ng v cc dng. Nhng in t ny c ng nng rt ln, v khi chuyn ng trong plasma gia hai in cc, cc in t va chm vo cc phn t khc (nguyn t, Ion, phn t...) trong plasma F, n truyn nng lng cho nhng phn t . Khi trong plasma c phn t b Ion ha, b phn li v b kch thch. Kt qu li c thm in t t do na cng vi mt s nguyn t, Ion, phn t b kch thch. Nh vy chnh cc phn t mang in tch dng v nm duy tr dng in qua ct kh ca plasma. Gia hai in cc F cc phn t b kch thch s sinh ra ph pht x ca n. Trong h quang mt chiu in t lun lun p vo in cc dng, nn in cc dng nng hn in cc nm. Cn ngc li, trong h quang dng xoay chiu, hai in cc li c t nng nh nhau.H quang dng mt chiu thng xut hin s st th hai u ca in cc. Hiu ng ny xut hin rt r rng trong thi gian u ca s phng in v h quang c dng thp (di 5A). Nhng sau c nng lng ca ngun kch thch b vo th s st th s gim i. Nguyn nhn ca s st th ny l do s xut hin lp in kp hai u ca in cc v lp in kp ny c t trng ngc vi t trng chnh ca h quang. Vi h quang xoay chiu, do dng in lun lun i chiu, nn s st th xut hin khng r rng v rt t c tc dng. chnh l l do gii thch ti sao s kch thch ph pht x bng h quang dng in xoay chiu lun lun n nh hn s kch ph trong h quang dng in mt chiu.Nhit ca plasma h quangYu t th nht, yu t chnh quyt nh nhit ca h quang l cng dng in trong mch h quang chnh. Trong mt khong nht nh ca nhit , khi tng cng ca dng in th nhit ca h quang cng tng theo. Ngha l ta c:T = k. I (2.2)Trong k l h s t l, T l nhit ca h quang (OC). Nhng n mt gi tr nht nh ca cng dng in I0, th nhit h quang tng rt chm theo s tng nhit (hnh 2.7). Gi tr I0 c gi l dng in gii hn ca h quang. Nhng cng dng in trong mch h quang thay i tng i mnh. V ct kh ca plasma lun thay i c v di v b rng, do im phng in trn b mt in cc lun lun di ng. l nhc im ca h quang. Do ngi ta phi dng in cc i c hnh nn ct.V vy, mun cho cng dng in I trong mch h quang n nh (t thay i) ngi ta phi mc trong mch h quang h in tr R2 tht ln, s thay i ca R1 do ct kh gy ra t b nh hng n I. V th trong cc my pht h quang ngi ta thng lm mt h in tr ni R2 rt ln v cng dng in c tnh theo cng thc:25_ + R(2.3)trong :R1: in tr ct kh ca plasma gia hai in cc.R2: in tr ni ca my pht h quang.U: Th ca ngun in ca my pht t ln hai u in cc F.Yu t th hai quyt nh nhit ca h quang l bn cht ca nguyn liulm in cc. Ni chung, nguyn liu no kh bay hi v cu to t nhng nguyn tha hc c th Ion ha cng cao, th h quang dng in cc nguyn t s cho nhit cng cao. V th h quang in cc than (graphite) s c nhit cao nht so vicc h quang in nguyn liu khc trong cng mt iu kin dng in th nghim(bng 2.2). Yu t th ba l th Ion ha ca cc cht c trong mu phn tch, ch yu lcht nn v nhng cht c nng ln. Ni chung, nguyn t no (nht l cht nn camu) c th Ion ha cng nh th cng lm gim nhiu nhit ca h quang, ngha lcc kim loi kim c tc dng mnh nht, sau n cc kim loi kim th. Chnh vth th ngi ta thng thm cc mui halogen ca kim loi kim vo mu gpphn iu chnh nhit ca plasma ca h quang cho s kch thch ph ca ccnguyn t phn tch. Bn cnh th Ion ha, th nng ca cc nguyn t cng c nhhng n nhit ca h quang, c bit l cc nguyn t c th Ion ha thp s lmgim nhit ca h quang cng nhiu, khi nng ca n trong plasma cng ln.Trong plasma ca hquang thng lun lun xy racc phn ng ha hc v vt l. l qu trnh phn li, Ion ha,t hp phn t v s kch thchph. Nhng qu trnh nythng l cc qu trnh nhitng hc v m hi trongplasma cng c mt nhit nht nh ng vi nhng thngs xc nh ca my pht hquang c chn. Nhit m bo cho plasma c mtp lc in t xc nh duytr s kch thch ph.

26S kch thch ph trong plasma h quang inTrong plasma ca h quang, s kch thch ph pht x c th xy ra theo cc qu trnh sau:Nu l mu dung dch, th trc ht l dung mi bay hi,licc htbtmu.Ri cc cht (c mu bt v b ca mu dung dch cnli),btmubnungnng, nng chy. Sau l cc qu trnh nhit ha ca cht mu xy ra theo tnh cht ca n. C th l cc ht mu s bay hi hay chuyn khi vo plasma gia 2 in cc. Ti y s xy ra cc qu trnh chnh v ph khc nhau, ty thuc vo thnh phn v bn cht ca cht mu.Numuldngbtc nhivo tronglinccmang th c cc qutrnh trong in cc mang mu l:+ S nung nng v nng chy,+ S chuyn ng nhit khuch tn v i lu ca cc ht trong l in cc,+ Cc phn ng ha hc phn hy ca cc cht mu km bn nhit,+ S bay hi ca cc phn t cht mu vo plasma,+ S vn chuyn ca cc ht mu cha ha hi vo plasm.Bn cht v thnh phn ca mu trong l in cc v nhit ca in cc l yu t quyt nh s din bin ca cc qu trnh trn.Sau l cc qu trnh trong plasma. Gm c 2 qu trnh chnh sinh ra ph pht x nguyn t (AES) v mt s qu trnh ph nh sau:A- Hai qu trnh chnh: Nu Eh < Ent th mu s ha hi, nguyn t ha to ra cc nguyn t t do, chng b kch thch v pht x ^ c ph pht x (AES)Men Xm(r) ^ Men Xm(k) ^ mMe(k) + nX(k)Me(k) + E ^ Me(k)* ^ MeO + n(hv)Nng lng K.Th.Chm tia pht xC ch 2 ny cho nhy v n nh cao ca s pht x. Cc hp cht mui halogen (tr F), axetat, mt s nitrat, sunphat,... ca kim loi thng theo c ch ny. Nu Eh > Ent th phn t ca cht mu s b nguyn t ha trc, sau ha hi thnh cc nguyn t t do, ri mi b kch thch ph ^ sinh ra ph pht x (AES).Men Xm(r) ^ Men (r) + Xm(r) ^ mMe(k) + nX(k)Me(k) + E ^ Me(k)* ^ MeO + n(hv)Nng lng K.Th.Chm tia pht xC ch 2 ny cho nhy v n nh km so vi c ch 1 ca s pht x. Cc27hp cht mui SiO3, PO4, F, mt s nitrat, sunphat... kim loi thng theo c ch ny.Do c im ca 2 c ch chnh , nn trong phn tch ngi ta thng to diu kin s kch thch ph xy ra theo c ch 1 c li. iu gii thch ti sao ngi ta hay dng cc mui halogen, v xetat ca kim loi kim lm nn, hay cht ph gia cho mu phn tch v mu chun, bin i nn mu gc sang nn nhn to tt hn v li cn loi tr c cc yu t nh hng, ng thi c khi cn tng c c nhy ln hng chc ln.B- Cc qu trnh ph:Trong plasma ca h quang thng c:S hnh thnh hp cht bn nhit, ch yu l cc monoxit (dng MeO).S Ion ha to ra cc Ion, ch yu l s Ion ha bc 1.S hp th bc x ca nguyn t (qu trnh t o).S pht x ph nn lin tc.Bn cht ca cht mu, thnh phn ca mu, cht ph gia trong l in cc v nhit ca in cc l yu t quyt nh din bin ca cc qu trnh trn.Ni chung cc qu trnh ny u khng c li, ngi ta tm bin php loi tr.V d:+ hn ch s hnh thnh hp cht bn nhit kiu MeO, ngi ta thm vo mu mui Clorua ca kim loi kim (nh KCI, CsCl,) lm nn, kch thch ph theo c chhoc kch thch ph trong mi trng kh tr argon.+ Hay loi tr s Ion ha ca nguyn t phn tch, ngi ta thm vo mu cht phgia muihalogen kimloikimcthIon ha thphnthIon ha canguyn t phn tch. Nh th nguyn t phn tch s khng b Ion ha na.Cc loi my pht h quangMy pht h quang c rt nhiu, c nhiu hng cung cp, song xt v c ch mch in ca mch h quang chnh, th c th chia thnh hai loi:+ My pht h quang dng mt chiu.+ My pht h quang dng xoay chiu.Tuy l hai loi, nhng u c nguyn tc cu to nh nhau (hnh 2.6). Trong mi loi h quang li c nhiu ch khc nhau. Thng thng c mt ch lin tc v nhiu ch gin on. Chnh v th m chng ta c th chn c nhng gi tr nng lng khc nhau cho tng mc ch phn tch c th.Tia la inc im v tnh chtTia la in l ngun kch thch ph c nng lng tng i cao. Ty theo cc thng s ca my pht tia la in (C, L, R, T) chn, ta c th t c nhit 28 tnm plasma tia la in t 4000 - 6000OC. V th tia la in c gi l ngun kch thch cng (giu nng lng). Nn ph pht x ca tia la in ch yu l ph ca cc Ion bc 1 ca cc kim loi.Tia la in l ngun kch thch tng i n nh v c lp li cao. Nhng v nhy li km h quang in. Do thi gian ghi ph cn phi di hn h quang.v bn cht ca s phng in, tia in l s phng in gia hai in cc c th hiu rt cao (10.000 - 20.000kV) v dng in rt thp ( Ent th phn t ca cht mu s b nguyn t ha trc, sau ha hi thnh cc nguyn t t do, ri mi b kch thch ph ^ sinh ra ph pht x (AES).Men Xm(r) ^Men (r) + Xm (r)^ mMe(k) + nX(k)Me(k) + E ^ Me(k)* ^ MeO + n(hv)Nng lng K.Th. Chm tia pht xC ch 2 ny cho nhy v n nh km so vi c ch 1 ca s pht x. Cc hp cht mui SiO3, PO4, F, mt s nitrat, sunphat,... kim loi thng theo c ch ny.Do c im ca 2 c ch chnh , nn trong phn tch ngi ta thng to iu kin s kch thch ph xy ra theo c ch 1 c li. iu gii thch ti sao ngi ta hay dng cc mui halogen v axetat ca kim loi kim lm nn, hay cht ph gia cho mu phn tch v mu chun, bin i nn mu gc sang nn nhn to tt hn v li cn loi tr c cc yu t nh hng ng thi c khi cn tng c c nhy ln hng chc ln.A2- Khi mu l thanh kim loi lm in mang+ Lpcc nguynttrn bmtincc, ditc dngcalcintrngin mnh (v th phng in rt cao gia 2 in cc, 15- 20 kV), nn cc nguyn t b bt ra khi mt in cc v bay vo plasma, hoc l dng hi, hay l dng ht rn. Sau c cc qu trnh sau:Ha hi ca ht rn:Men) + E1 ^ Me(k)Nguyn t b kch thch:Me(k) + E2 ^ Me(k)*Nguyn t b Ion ha:Me(k) + E3 ^ Me(k)+Ion b kch thch:Me(k)+ + E4 ^ Me(k)+*31Pht x ca nguyn t:Me(k)* ^ Me(k) + n(hv)Pht x ca Ion:Me(k)+* ^ Me(k) + n(hv)Trong : n(hv) l chm tia pht x ca nguyn t hay Ion b kch thch.Cn El, E2,.. l nng lng nhit do plasma tia in cung cp.B- Cc qu trnh phTrong plasma gm c:S hnh thnh hp cht bn nhit, ch yu l cc monoixtit (dng MeO).S Ion ha to ra cc Ion, ch yu l s Ion ha bc 1.S hp th bc x ca nguyn t (qu trnh t o).S pht x ph nn lin tc.Bn cht ca cht mu, thnh phn ca mu, cht ph gia trong l in cc v nhit ca in cc l yu t quyt nh s din bin ca cc qu trnh trn.Song qu trnh ph trong plasma tia in khng mnh nh trong ngn la v trong h quang, ch c s Ion ha l ng k. V th cc kim loi kim phi o theo cc vch Ion bc 1.Ni chung, cc qu trnh ny u khng c li. Ngi ta phi tm bin php loi tr. V d vi mu dung dch:+ hn ch s hnh thnh hp cht bn nhit kiu MeO, ngi ta thm vo mu mui Clorua ca kim loi kim (nh KCI, CsCL,) lm nn, kch thch ph theo c chhoc kch thch ph trong mi trng kh tr argon.Vy, loi tr s Ion ha ca nguyn t phn tch, ngi ta thm vo mu cht ph gia mui halogen kim loi kim c th Ion ha thp hn th Ion ha ca nguyn t phn tch. Nh th, nguyn t phn tch s khng b Ion ha na.Cc loi my pht tia inV nguyn tc cu to, my pht tia la in cng c hai loi: my pht tia la in c ch huy v my pht tia la in khng ch huy. Song trong mc ch phn tch quang ph pht x, ngi ta ch dng my pht tia in c ch huy. Trong loi my pht ny, vic ch huy (iu khin) cng theo hai nguyn tc v ng vi hai cch iu khin ny ngi ta ch to hai loi my pht tia in khc nhau:+ My pht tia in dng hai tia in, tia in chnh, tia in ph (hnh 2.9), tng t nh my h quang.+ My pht tia in dng ngt in ng b (hnh 2.10), ngha l iu khin bng m t ng b.My pht tia in dng hai tia din (hnh 2.9)32Trong my ny c mt tia in chnh v mt tia in ch huy. Theo s hnh2.9, khi ng mch in K, bin th Tr c np in v tng th ln hng ngn vn(V). Lc h t in C c tch in v th hai ct ca t C l th ca khong ngia hai qu cu E. Lc ny trn mch in LC khng c dng in, t C c tchin cho n khi t c th Vf (th phng in gia hai qu cu E) th tia in snh qua hai qu cu E, t C phng in qua E lm cho trn mch dao ng LC xuthin tc khc mt dao ng cao tn, dao ng ny khng qua c L2 (hay Ri); do bt buc phi nh qua khong n F (khong cch gia hai in cc chnh). Nh vy,h c mt dao ng v mt tia in nh E, th cng c mt tia in phng qua F,ngha l tiain E iu khintiain F. Sau qu trnhc thtipdin chon khi ta ngt cng tc K.Mun cho qu trnh phng inc n nh th hai qu cu E phi ckch thc xc nh, khong cchkhng i v b mt phi nhn. Cnh th in th Vf mi c nhng gitr xc nh ng vi tng cp thng sca my pht tia in c chn, m bo cho qu trnh phng in F n nh v mt nng lng, v chai tia in xy ra ng thi, nn nngHrnh 2 9lng phi chia i hai khong n Eb ^,7bMy pht tiain dng hia tia inv F. V th mun c nng lng ln(nhit cao) th th Vf phi rt ln.My pht dng ngt in ng b (hnh 2.10).My pht loi ny ch totheo s ca Fressner. y sphng in c ch huy nh mtm t ng b c gn b ngt inmc ngay trn mch ca my phttia in. My pht gm bin th Tr tng th, mch dao ng LC,khong phng in chnh F, haicun cm Li5 L2 ngn khng chodao ng cao tn tr v bin th Trv m t ng b M ng vm mch in ca qu trnh phng Hnh 2.10in gia 2 in cc F.Myphttiain dng ngt in ng b

33Khi cho in vo my, bin th Tr tng in, t C c tch in dn, m t M quay u c mang theo hai tip im A v A, cng quay, khi n v tr B v B1 mch in trong my c ng, lc th t C cng t cc i, khin cho tia in phi phng qua F, sau tia in li tt. Nhng v m t M quay u lin tip, nn tia in cng nh u n lin tip qua F theo s quay ca mt M tun hon n v tr B v B1 ln lt theo thi gian chu k c chn, cho n khi no ta ngt cng tc K. Nh vy, chnh m t ng b M iu khin s phng in theo cc thng s c chn.Plasma cao tn cm ng ICPc im v tnh chty l ngun nng lng mi c s dng trong php phn tch quang ph pht x nguyn t khong 10 nm li y; song li c s dng rng ri v c hiu qu cao v n c nhng c im sau y:Ngun nng lng ny c nhit cao. Thng thng tnm ca plasma c th t c nhit t 5000 - 10000OC nn ha hi v nguyn t ha c ht mi trng thi ca vt liu mu vi hiu sut cao. Vi plasma ny, mi nguyn t kim loi u b kch thch to ra ph pht x ca n. Cc hp cht bn nhit cng b ha hi v phn li thnh nguyn t t do, nhng trong ngun nng lng ny ph pht x ca Ion l ch yu.ICP (Inductivity Coupled Plasma) l ngun nng lng kch thch ph pht x m bo cho php phn tch c nhy rt cao. Ni chung c th t t n.10-4: n.106% (0,l - 5) ngng i vi hu ht cc nguyn t. Tt nhin nhy ca php phn tch y ph thuc nhiu vo cng sut ca my pht cao tn HF to ra plasma ICP (hnh2.11).ICP l ngun kch thch ph khng nhng c nhy cao, m cn c n nh cao. N hn hn h quang v tia in. V th php phn tch dng ngun nng lng ny cho sai s rt nh; ni chung l nh hn 10% trong vng nng t n.10-3- n.10-5%.34kW1234Hnh 2.11S ph thuc ca cng vch ph vo cng sut my pht cao tn ICP

Tuy c nhit cao nhng s kch thch ph pht x trong ngun nng lng ny li rt m du. N tng t nh s kch thch ph trong ngn la n kh. Chnh v th m phng php phn tch t n nh cao v sai s nh.Vi ngun nng lng ny, ngi ta c th nh lng c ng thi nhiu nguyn t mt lc, nn tc phn tch rt cao (t 40 - 120 mu/gi). Mt khc, khi dng ngun nng lng ICP, vng tuyn tnh ca phng php nh lng l rt rng (t 1 - 10.000 ln).c im cui cng l rt t xut hin nh hng ca cht nn (matrix effect). l im hn hn cc ngun nng lng c in nu.Chnh do nhng c im v u vit ca ngun nng lng ICP nh th, nn n nhanh chng c ng dng rng ri v thay th cho ngun nng lng c in: tia in v h quang. Tt nhin, trang b to ra ngun nng lng ny t hn. Nhng trong iu kin ngy nay v do tnh cht u vit ca n nn cc phng phn tch quang ph pht x u c trang b loi ngun nng lng ny.Cu to ca h thng 1CPV nguyn tc, h thng thit b to ra ngun nng lng ICP gm hai phn chnh: my pht cao tn HF v h thng to th si kh v n nguyn t ha kch thch ph ca mu phn tch.My pht cao tn HFCc my ny lm vic tn s rt cao nhng ph bin l hai tn s 27,12 MHZ v 450 MHZ. Trong my trung tn s 27,12 MHZ c s dng nhiu hn. l tn s sng mang rai. My pht cao tn HF c nhim v pht tn s cao cung cp nng lng cho cun cm cao tn u ming n nguyn t ha mu, to ra plasma nhit cao cho s ha hi mu, nguyn t ha v kch thch ph (hnh 12a).35

Phn th hai ca h thng ICP l b phn nguyn t ha mu, bao gm b phn to soi kh mu v n nguyn t ha mu (nebulizer system v khch bumer). B phn burner c ch to bng thch anh chu nhit. N gm ba ng lng vo nhau, gn chc vo nhau phn y, v mi ng u c ng dn kh vo (hnh 2.12a). Trong , ng trong cng l mt ng mao dn dn mu vo plasma nh kh mang; ng th hai l ng to ra kh plasma. Cn ng th ba l ng to kh lm lnh cho n nguyn t ha. Pha ngoi ng th ba v ngay u c cun cm cao tn bng ng. Cun cm ny c ni vi my pht cao tn HF v lun c lm lnh bng dng nc chy qua khi lm vic. ng thi chnh cng sut lm vic ca cun cm ny s quyt nh nhit ca plasma kch thch ph. Cn h thng nebulizer, v nguyn tc, hon ton tng t nh trong ngn la n kh nu trn.Kh dng trong plasma ca ICP l cc kh tr nh argon, hli, nit. Trong argon l u vit nht. y ngi ta c th dng kh mang v kh plasma l argon, cn dng nit lm lnh. Hoc c th dng ch mt kh Ar cng c. Trong tng lng kh cho c ba dng l t 13 - 18 lt/pht v c phn chia nh nhau:Kh mang: 0,7 - 1,0 l/pht.Kh plasma: 6 - 8 l/pht.Kh lm lnh: 5 - 9 l/pht.Nhng ngy nay, ngi ta ci tin v dng loi mini - ICP nn ch cn n 1/3 lng kh so vi loi thng thng nu.

Hnh 2.12aH thng ngun ca ICP-AESNhit ca plasma ICPICP l ngun nng lng kch thch ph c nhit cao, nhng li n nh hn so vi cc loi ngun kch thch khc, nh h quang, tia la in. Nhit ca plasma ca ngun ny c quyt nh bi dng in cm ng trong cun cm A u ca n nguyn t ha, tc l nng lng cao tn ca my pht HF. V vy, ng vi nhng thng s nht nh ca my pht HF th plasma ny c mt nhit xc nh. Trong cc thng s ca my pht HF, cng sut v tn s cm ng l hai thng s quan trng36nht. Song mi my pht thng ch dng mt tn s cm ng nht nh 27,12 MHZ hay 450 MHZ, nn cng sut ca my pht ng vai tr chnh. V th cng ca vch ph ph thuc vo cng sut ca my pht HF (hnh 2.11).Tt nhin, bn cnh cn c nhng yu t khc nh hng n nhit ca plasma ICP. Trc ht l tnh cht ca kh plasma, kh mang v tc chy ca chng vo plasma. Sau l thnh phn ca hn hp mu c dn vo plasma kch thch ph. Ni chung dng lin kt, th Ion ha ca cc nguyn t cng c nh hng n nhit ca plasma. Nhng cc yu t ny khng mnh nh trong h quang v tia in. Yu t matrix effect cng c tc dng, nhng cng khng ln nh trong ngn la n kh v trong h quang in. Cc yu t trn nh hng n nhit ca plasma, tc l nh hng n cng ca vch ph. Nhng khi chn c cng sut ln ph hp, th nh hng ny s rt nh, hay khng cn na.S kch thch ph pht trongplasma ICPKhi ta ng mch in ca my pht cao tn HF th cun cm A u n s xut hin tc khc dng in cao tn cm ng c nng lng ln. Nng lng ny c quyt nh bi cc thng s ca my pht HF c chn. ng thi tia la K cng c bt, hn hp kh v mu c t chy, plasma nhit cao xut hin, ngha l ngn la hnh thnh. Trong ngn la nhit cao ny, trc ht dung mi bay hi ( phn trong, phn ti ca ngn la), li cht mu dng ht bt mn. Ri cc bt mu ny b nung nng, nng chy, c ha hi, phn li, b nguyn t ha v Ion ha to ra trong plasma c phn t, nguyn t, Ion, in t trng thi kh. Trong ch yu l cc nguyn t, Ion v in t. Sau cc phn t kh ny c trong plasma s b kch thch v sinh ra ph pht x. Bn cht s kch thch ph y l s kch thch nhit, n ging nh s kch thch ph pht x trong ngn la n kh. Nhng v plasma c nhit cao (nng lng ln) nn hiu sut nguyn t ha v kch thch ph cao v ph ca ngun nng lng ny vi cc kim loi kim v kim th ch yu l ph ca cc Ion bc 1. C ch ca qu trnh trong plasma ICP c th tm tt theo s sau:37

Hnh 2.12bHai loi my o ph pht x ICP (ICP-AES)HF: My pht cao tn; Pm: H thng nguyn t ha mu; L: Thu knh; T: Khe sng; G: Cch t; PM: H nhn quang in; >>: H in t; Mr: My tnh; Sig: B ch th kt qu o; AB: Cung mt phng tiu; Mh M2: cc gng chun trc v hi t.Trc ht l dung mi bay hi, li cc ht bt mu. Tip theo l bt mu b nung nng, nng chy. Sau l cc qu trnh nhit ha ca cht mu xy ra theo tnh cht ca n.Ba qu trnh chnh: Cc qu trnh chnh y cng tng t nh trong ngn la n kh. Nhng c khc ngn la n kh l hiu qu ha hi, nguyn t ha v kch thch ph cao hn nhiu.Nu Eh < Ent, th mu s ha hi, nguyn t ha to ra cc nguyn t t do, chng b kch thch v pht x ^ c ph pht x (AES).Men Xm(r) ^ Men Xm(k) ^ mMe(k) + nX(k)38Me(k) + E ^ Me(k)* ^ MeO + n(hv)Nng lng K.Th.Chm tia pht xC ch 1 ny cho nhy v n nh cao ca s pht x. Cc hp cht mui halogen (tr F), axetat, mt s nitrat, sunphat,.. ca kim loi thng theo c ch ny.Nu Eh > Ent, th phn t ca cht mu s b nguyn t ha trc, sau ha hi thnh cc nguyn t t do, ri mi b kch thch ph ^ sinh ra ph pht x (AES).Men Xm(r) ^ Men(k) + Xm(k) ^ mMe(k) + nX(k)Me(k) + E ^ Me(k)* ^ MeO + n(hv)Nng lng K.Th.Chm tia pht xC ch 2 ny cho nhy v n nh km so vi c ch 1 ca s pht x. Cc hp cht mui SiO3-2, PO4-3, F, mt s nitrat, sunphat... ca kim loi thng theo c ch ny. S Ion ha sinh Ion, sau cc Ion b kch thch v sinh ra ph ca n.C th l:Men Xm(r) ^ Men Xm(k) ^ mMe(k) + nX(k)Me(k) + Ei ^ Me(k)+ + e Me(k) + E ^ Me(k)+* ^ MeO + n(hv)Nng lng K.Th. Chm tia pht xV trong ngun ICP c nhit cao, nn cc kim loi c th Ion ha thp s din ra theo c ch ny, v d cc kim loi kim, kim th.Qu trnh ph gm c:+ To ra cc hp cht bn nhit, ch yu l cc monoxit (dng MeO). Nhng trong plasma ca ngun ICP th cc qu trnh ny xy ra khng ng k. chnh l u vit ca ICP.+ S hp th bc x ca nguyn t (qu trnh t o).+ S pht x nn (nhng cng nh).+ SIon habchaica nguyn tkimloikimv cc nguyn t cth Ionha bc hai thp.39

Ht muHa hiNguyn t haIon haKch thch ph (nu Ehh < Engt)Hnh 2.13 S qu trnh nguyn t ha muNguyn tc v cch chn ngun kch thch phCc iu kin kch thch ph l nhng yu t c nh hng trc tip n cng ca vch ph v nhy ca phng php phn tch. V th chn ng cc iu kin kch thch ph l mt m bo cho phng php phn tch t kt qu chnh xc, tin cy v nhy cao. Mt khc, qua vic chn c iu kin kch thch ph ph hp ta c th loi tr c mt suyn t nh hng, nh matrix effect, nng cao nhy. Do chn c nhng iu kin, ngun kch thch ph ph hp cho mt i tng phn tch no chng ta phi da theo mt s nguyn tc c bn sau y:Phi xut pht t i tng phn tch thuc dng mu no (mu bt, mu rn, mu dung dch hay hp kim), cng nh nhng tnh cht c l ca tng loi mu thuc loi mu d bay hi hay kh bay hi, dn in hay khng dn in. V d khi phn tch mu bt (qung, t ,...) th h quang c dng trn 10A l thun li. Song khi phn tch mu hp kim th tia in li u vit. Mu dung dch dng ICP.Phi da theo tnh cht v c trng s kch thch ph ca mi nguyn t cn xc nh m chn ngun nng lng kch thch v cc thng s ca ngun kch thch. V d phn tch kim loi kim th nn dng ngn la n kh hay h quang gin on.V th kch thch ph pht x ca cc kim loi kim l khng ln (3 - 5eV).

40Ngc li, vi cc nguyn t V, Zn, W,... hp cht bn nhit, li phi chn ngun kch thch c nng lng cao, h quang in dng ln hay ngun ICP.Khi chn ngun kch thch phi m bo cho php phn tch c nhy cao, n nh, c th d dng phn tch c cc nguyn t c nng nh.Chn ngun kch thch phi m bo cho php phn tch tiu tn t mu v khi cn phi khng ph hy mu. Yu t ny trong mt s trng hp khng yu cu, bt buc nh ba yu t trn.Cng vch ph pht x nguyn tCng vch ph :Trong ngun pht sng hay trong plasma, nguyn t (Ao) ca mt nguyn t c kch thch t trng thi nng lng thp Eo, ln trng thi nng lng cao. Cm c biu din theo phng trnh:Ao + XE = A* (a)Vi mu phn tch c nng xc nh ca Ao th qu trnh ny lc u tng nhanh, sau chm dn v ti mt thi im nht nh th khng tng na. Ngha l s nguyn t Ao b kch thch l khng i, ng vi mt nhit xc nh ca plasma. ng thi vi qu trnh trn l qu trnh ngc li, tc l nguyn t b kch thch A* gii phng nng lng m n nhn c di dng cc tia pht x n(hvi) tr v trng thi nng lng thp bn vng ban u. Chnh qu trnh ny l qu trnh pht x ca nguyn t v sinh ra ph pht x ca nguyn t, c th c biu din theo phng trnh:A* = hv + Ao (b)Qu trnh ny lc u chm, sau tng dn theo s nguyn t A* b kch thch v n mt thi im nht nh th cng khng tng na ng vi mt nhit nht nh ca plasma. Ngha l sau mt thi gian nht nh ca s kch thch ph, th hai qu trnh trn (a) v (b) s t n trng thi cn bng. l hai cn bng ng hc thun nghch. Cn bng ny ch ph thuc ch yu vo nhit ca plasma, ngha l s nguyn t A* b kch thch v pht x l khng i, ng vi mt nhit xc nh ca plasma.Nu gi Nm l s nguyn t ca nguyn t Ao b kch thch n trng thi nng lng cao cm, th theo quy lut Bolzmans ta c:N = N gme(-E )/Ktma_vm'g 0go vgml trnglngthng kcanguyn tA trngthi banu,nnglng Eo v trng thi kch thch nng lng cm;Na l s nguyn t ca nguyn t Ao c trong plasma (trng thi hi);41Em l nng lng kch thch nguyn t o t trng thi Eo ln trng thi cm;T l nhit ca plasma (oK);k l hng s Bolzmans.Nu gi Ia l cng ca vch ph do qu trnh kch thch ph ni trn sinh ra, th trong mt gii hn nht nh ca nhit plasma v nng ca nguyn t Ao trong plasma, ngi ta thy Ia ph thuc vo:S nguyn t Ao b kch thch ln trng thi A*, (Nm).Thi gian tn ti ca nguyn t A* trng thi kch thch, (trn).Nnglngkch thch nguyntAttrngthicbnntrngthi kchthch, (Em). Xc sut chuyn mc ca nguyn t A t trng thi kch thch nng lng Cm v trng thi ban u nng lng Eo, (Amo).V mi quan h ny c th biu din theo cng thc sau:Ia = f. f .Amo A . ^-hv.e-(E)/kTt gmoNhng i vi mt loi nguyn t v trong mt iu kin th nghim nht nh ca plasma (ch yu nhit plasma) th cc yu t tri Amo, go, gm, cm, hv l nhng hng s.Cho nncng vch ph Ia chcnphthucvo s nguyntbkchthch Na m thi. Nh vy ta c:Ia = K Na(2.6)Vika = f. t-. Amo .Aa . ^ .hv.e-(E)/kTtgmo o l cng vch ph ca nguyn t.Song cng thc (2.6) mi ch cho ta bit mi quan h gia cng vch ph Ia v nng ca nguyn t trng thi hi trong plasma, m cha ch cho ta c mi quan h gia cng vch ph v nng ca nguyn t trong mu phn tch. Mun th ta phi xt mi quan h gia nng C trong mu v s nguyn t Na trong plasma. Ni chung, mi quan h ny l phc tp, n ph thuc vo nhiu yu t, nh:Kh nng ha hi, bn cht ca cht mu, cht nn;Thnh phn ca mu, cht ph gia thm vo;Trng thi lin kt, tn ti ca cht mu;Cc iu kin ha hi, nguyn t ha mu, kch thch ph;Mi trng kch thch ph, v.v...Tuy nhin ngi ta thy t thc nghim, trong mt phm vi nht nh ca nng42 C th ta lun lun c:Na = k2.Cb (2.7)Nh vy, cng vch ph s l:Ia = a.Cb (2.8)Trong : a: k1.k2 v a c gi l hng s thc nghim. N ph thuc vo tt c cc iu kin thc nghim ha hi, nguyn t ha v kch thch ph mt nguyn t. V th trong mt php phn tch phi gi cho cc iu kin thc nghim n nh, m bo a thc s l hng s ca php o. Cn b l hng s bn cht, n ph thuc vo bn cht ca tng loi nguyn t, b ch nhn nhng gi tr bng 1 v nh hn 1, nhng ln hn 0. Gi tr ca b nh hn 1 khi nng C ln, cn khi C nh th b lun lun bngKhi b nh hn 1 l lc qu trnh t hp th xy ra. Qu trnh t hp th xy ra cng nhiu (mnh) th b cng nh xa 1, tc l chnh hng s b l c trng cho qu trnh t o ca mi loi nguyn t. Do , ng vi mi nguyn t v vi mi mt vch ph pht x v trong nhng iu kin nht nh, ta lun c mt gi tr nng Co, m:+ Khi vi mi Cx < Co th b lun lun bng 1.+ Khi vi mi Cx > Co th b nh dn xa 1 (hnh 2.14).Trn y cp n cng ca vch ph nguyn t trung ha nhng trong plasma cn c c cc Ion. Chng cng b kch thch v sinh ra ph pht x. Qu trnh kch thch v pht x cng ging nh cc nguyntvcng tnh ton hon tontng t nn chng ta c cng vch ph Ion l:li = Al. Cb (2.9)

01234567Hnh 2.14Quan h gia cng vch ph v nng cDo , mt cch tng qut, ta c th vit cng vch ph pht x: I = a.Cb(2.10)43Cng thc (2.10) l phng trnh c bn ca phng php phn tch nh lng theo ph pht x nguyn t. Phng trnh ny do Lmakins (Nga) v Saiber (c) tm ra, nn gi l phng trnh Lmakins-saiber.Cng vch ph v nhit plasmaNh trn chng ta bit, cng vch ph pht x ca nguyn t c tnh theo biu thc sau: Ia = Pa.N(l-x)e-E(m)/kTV vch Ion:Ii = Pi.N.x.e-Em/kT(2.12)lgTrong , vi:Pa = Aam .hvtgamo oiu ny cho thy cng ca vch ph ph thuc vo nhit ca plasma.Nhng, tt nhin, s ph thuc ny i vi vch nguyn t v vch Ion l khc nhau v khng n iu, m theo hm s m (e-Em/kT). Chnh hai cng thc trn d dng cho ta thy rng, nhit no ca plasma to ra c s nguyn t N(1 - x) trong cng thc tnh cng vch nguyn t v s phn t (N.x) trong cng thc vch ph ln l ln nht, th lc s c c cng ca vch ph ln nht. l nhit ti u ca s kch thch ph.

100200300100200300400Ca: 4226,70 /nn Al203; Ca: 4226,70 /nn Si02 AI: 3093,00 ; Mg: 2852,19 ;Si 2516,00 A;Sn: 2355,00 .Hnh 2.15S ph thuc ca cng vch ph vo nhit trung tm plasma44Vi mt vch ph ca mt nguyn t, thc t ch c mt nhit to ra c cng I cc i. Nhit ny c gi l nhit ti hn ca vch ph v c khiulTo.Ttnhinivimivch th nhit To ny khc nhau (hnh2.15a,b,c). Ngay i vi vch ph ca mt nguyn t, nu n tn ti trong cc nn mu khc nhau (matric khc nhau) th nhit To ny cng khc nhau (hnh 2.15c). iu c nghal, ngoibncht cachtphn tch, nhitTocnphthuc vocthnh phn v nn ca mu phn tch.Tnh cht ny c ngha thc t rt ln khi xc nh lng nh cc nguyn t trong mu phn tch. V trong nhng trng hp ny ta cn phi chn nhng iu kin lm vic v iu kin kch thch ph sao cho thu c vch ph c cng ln nht, tc l chn cc iu kin kch thch ph c c nhit ca plasma gn vi nhit To ca vch ph cn o, hoc bng ng c To l l tng. Tt nhin bng c l trng hp rt him, ta ch c th lm cho nhit ca plasma cng gn vi nhit To th cng tt.Hin tng t hp th (t o) trng thi hi trong plasma, hin tng mt nguyn t c kh nng hp th tia bc x do chnh mt nguyn t khc cng loi ca chng pht ra c gi l hin tng t hp th (hay t o). Hin tng ny xy ra theo nh lut Kirschhoff. Ngha l mt nguyn t ch hp th nhng tia bc x m chnh n c th pht ra c trong qu trnh pht x. Hin tng ny thng xy ra mnh v ch yu i vi cc vch cng hng, vchcuicng caphphtx camtnguyn t, v nng cngln, th hin tng ny xy ra cng mnh. Chnh do hin tng ny, m a n kt qu lm cho cng vch ph pht x I khng ph thuc tuyn tnh vo C, khi nng C tng gi tr Cx > Co, Gi tr Co c gi l nng gii hn, cn c quan h gia I v C l tuyn tnh. Vi mi vch ph, Co l khc nhau. Vch cng nhy th Co cng nh. ng thi, trong qu trnh pht x, cng sut pht x ca mt vch ph c tnh theo cng thc:W = f.Wo(2.13)vi f l h s hot ng pht x ca vch ph v n nhn gi tr: 0 < f < 1.Khi khng c hin tng t o, ngha l nng Cx nh hn Co th f = 1, tc l W = Wo. Cn mi trng hp khc, khi c hin tng t o th lun lun c W < Wo. Trong :o = j Am .Na .hv.e-EmkT )dv(2.14)0 y: Na l s nguyn t trong n v th tch V ca plasma.Amo l xc sut chuyn mc;Cm l nng lng kch thch trng thi mi T l nhit ca plasma (oK);45hv l lng t sng c bc x ra; k l hng s Bolzmans.V ngha thc t, khi hin tng t hp th xut hin, ni chung u khng c li cho php phn tch ph pht x nguyn t. iu c ngha l trong phn tch khng nn xc nh mt nguyn t vng nng bt u xut hin hin tng t o, tc l nm ngoi vng tuyn tnh, phi pha long mu kt qu s chnh xc hn.Bc x nn trong ph pht xKhi kch thch mu phn tch ta thu c ph pht x ca n. Ph ny gm c ph vch ca nguyn t v Ion, ph m ca phn t v nhm phn t. Sau n ph nn hay gi l bc x nn. Bc x nn thng l ph lin tc. N to thnh mt di en m trn ton b vng ph ca mu phn tch. en ca di ph nn ny mi vng ph l khc nhau. Thng thng vng sng di m hn vng sng ngn. Nhn chung, n tng dn t vng sng ngn sang vng sng di, n th hin r rt vng kh kin (360 - 500 mm). Cn vng t ngoi (UY) th ph nn thng rt nh.Trong mt mc va th bc x nn l c li v n lm nn cho vch ph xut hin ln trn m hn, ngha l lm tng cng ca vch ph. Do , trong mt s trng hp nn qu yu ngi ta thng phi chiu sng ph knh nh bng nh sngtrngvimtthigian phhp. Song trong nhiutrnghpphnnthng qu mnh, c bit l trong vng kh kin v khi dng h quang. Lc ny n che lp mt vch ph ca nguyn t phn tch, nht l nng nh. Trong trng hp ny ngi ta phi tm cch kh bt bc x nn. Vy nguyn nhn no gy ra bc x nn ?T nhng kt qu nghin cu ngi ta thy c cc yu t sau y to ra bc x nn (ph nn):S pht sng ca ht vt rn c t nng trong plasma.Tc dng ca nh sng trng.S bc x ca in t trong plasma nhit cao.Do in cc b t nng sng v pht x (vt rn pht sng nhit cao).Trong ba yu t ny, yu t th ba th hin khng r nt bng hai yu t u. loi tr bc x nn ngi ta c th p dng nhiu bin php khc nhau. V d vi nguyn nhn th nht, ngi ta dng mn chn trc khe sng khng cho nh sng do hai u in cc c t nng chiu vo khe my quang ph. Hoc cng c th thm cht ph gia vo mu phn tch kh bt mt phn cng nn, lm cho nn ca ph khng qu en. Nhng tt nht l kch thch ph trong mi trng kh tr Ar (argon) hay hn hp ca kh tr Ar v oxy theo nhng t l ph hp. Bin php ny loi tr c c ph nn v ph xm ca nhm CN v ph phn t H2O, mt khc li cn tng c cng vch ph, ngha l tng c nhy ca phng php phn tch. l u vit ca mi trng kh tr trong s kch thch ph pht x nguyn t.46Chng 3MY QUANG PH V S PHN LI CHM SNGNguyn tc cu to ca my quang ph pht xMy quang ph l mt dng c dng thu, phn li v ghi li ph ca mt vng ph quang hc nht nh. Vng ph ny l mt i ph ca vt mu nghin cu t sng ngn n sng di. Ty theo b phn dng phn li nh sng trong my da theo hin tng vt l no (khc x hay nhiu x) m ngi ta chia cc my quang ph thnh hai loi.My quang ph lng knh. l nhng my quang ph m h tn sc ca chng c ch to t 1 hay 2 hoc 3 lng knh. S phn li nh sng y da theo hin tng khc x ca nh sng qua hai mi trng c chit sut khc nhau (khng kh v thy tinh hay khng kh v thch anh).My quang ph cch t. L nhng my quang ph m h tn sc l mt cch t phng hay lm phn x. Bn cht ca s tn sc nh sng y l s nhiu x ca tia sng qua cc khe hp.Tuy c 2 loi my quang ph khc nhau, nhng v nguyn tc cu to th u nh nhau, u gm 3 phn chnh. l h chun trc, h phn li v h hi t chm sng (hnh 3.1).H chun trc v phn u ca my quang ph. N gm mt hay mt hthng thu knh ghp vi nhau hay h gng hi t v mt khe hp (khe vo ca chm sng v c th iu chnh c) t tiu c ca h thu knh ny. H chun trc c nhim v nhn v to ra chm sng song song hng vo h tn sc phn li thnh ph.Htnsc. lmth thnglngknh hay mttm ccht.H ny cnhim v phn li (tn sc) chm sng a sc thnh cc tia n sc, tc l phn li mt ngun sng phc tp nhiu bc sng khc nhau thnh mt di ph ca chng theo tng sng ring bit lch i nhng gc khc nhau. Nu h tn sc c ch to bng lng knh th chng ta c my quang ph lng knh. V ngc li, nu h tn sc l cch t ta c my quang ph cch t. Trong my lng knh, tia sng ngn s b lch nhiu, sng di lch t, cn trong my cch t th ngc li.47

-1^> (a1 + a2 + Aa3).(f1/f2) th chng ta li c E - Eo, ngha l tri trng hp c bit trn. Tc l cng vch ph khng ph thuc vo rng ca khe sng. Cn tt c cc trng hp khc th rng ca vch ph t hoc nhiu u c b nh hng bi rng ca khe sng. V cng vch ph trong cc trng hp lun lun phi tnh theo cng thc:IX= E.t = Etja(3.25)[a + ([ + a2 + a3).(f / f2)]Cho nn khi khe my thay i th rng ca vch ph cng thay i theo. Nhng mi quan h ny khng n iu v cng khng tuyn tnh. V vy, trong mt php phn tch bt buc phi gi cho khe sng c rng khng i trong mt php o.Mt khc, cng thc (3.23) v (3.25) cn cho thy, ngoi rng ca khe sng, cng ca vch ph cn ph thuc vo c khu ca my quang ph, tc l t s d/f2. Cng vch ph s ln, nu my quang ph c khu ln. Ngha l tiu c thu knh bung nh phi nh. Nhng nu tiu c thu knh bung nh f2 nh, th li mt v tn sc di. Chnh v th trong ch to my quang ph ngi ta phi tnh tm c gi tr khu sao cho ph hp nht, nhm bo m c tn sc m cng ca vch ph cn ln c th o c v pht hin c d dng.Nu ly gi tr nghch o ca khu th ta c t s f2/d. T s ny gi l m ca thu knh bung nh. Trong thc t khi ch to cc my quang ph ngi ta thng hay chn t s ny c gi tr t 10 n 20. Tri li, khi m ln hn 20, vch ph c cng ln, nhng tn sc ca my li qu km. sng ca vch ph pht xNu ta pht hin v o trc tip cng ca vch ph bng mt nhn quang in, th sng ca vch ph l yu t quan trng. sng ca vch ph ph thuc vo cng ca chm sng i vo my quang ph v cng ca chm sng sau khi qua my quang ph vo nhn quang in. V th cu to, tnh cht ca h quang hc ca my u c nh hng n sng ca vch ph. Mt cch gn ng v theo thc nghim, sng ca vch ph c th c tnh theo cng thc:L = (d2/f2)2(3.26)Trong d2 v f2 l ng knh v tiu c ca thu knh bung nh. Nh vy, sng ca vch ph t l thun vi bnh phng ng knh ca thu knh bung nh d2 v t l nghch vi bnh phng ca tiu c bung nh f2, ngha l ph thuc vo m ca thu knh bung nh (t l f2/d2). Nu tiu c f2 cng ln th sng L ca vch ph cng gim, tc l mt v cng v ngc li.S quang hc mt s my quang ph lng knhV d v cc s h quang hc ca mt s my quang ph pht x c ch ra trong hnh 3.7.60

se) My KC - 55 (Nga)Hnh 3.7S quang hc ca mt s my o ph pht xP: Lng knh; G: Cch t; M, Mi, M2: Cc h gng; L: Thu knh; E: Hp nh ghi ph; T: Khe sng; S: Ngun pht x.Cch t v my quang ph cch tGii thiu v cch tCch t l h gm nhiu khe hp (vch) song song vi nhau v cch u nhau.Mi khe nh l mt chn sng, cn ch khng c vch nh l mt khe sng. Cch t c tc dng phn li nh sng nh lng knh. Nhng bn cht s phn li nh sng cch t khc lng knh. S phn li nh sng ca cch t l do hin tng nhiu61x ca chm sng qua khe hp. Khi s phn li nh sng ca lng knh l theo hin tng khc x ca nh sng qua hai mi trng c chit sut khc nhau. Cch t c hai loi:Cch t phn x v 2. Cch t truyn x. ch to my quang ph ngi ta thng dng cch t phn x, v dng cch t truyn x s b mt nhiu nng lng khi chm sng i qua cch t.Trong mi loi trn li c cch t phng v cch t lm. T thc t chng ta s ch cp n cu to v bn cht ca cch t phn x l chnh (hnh 3.8a v 3.8b).

Hnh 3.8aHnh 3.8bDch t phngCch t lm phnxCc i lng c trng cho mt cch t l hai thng s chnh sau y:Chu k ca cch t: L khong cch gia hai vch trn cch t v c k hiu l d (hnh 3.8a).Hng s cacch t: L s vch trn mt n v dica cch t v c khiu l k, tc l s vch ckhc trn1mm.Nh vy, gia chu k v hng s ca cch t lin quan vi nhau theo biu thc: d. k = 1(3.27)Nu gi L l chiu di ca cch t, th tng s vch trn mt cch t s l:N = k. L(3.28)v cu to th cch t phn x gm c hai phn. l b v mt cch t. B l tm thu tinh hay thch anh dy t 1,5 n 2 cm, c hai mt song song vi nhau v thng c din tch t 4 x 4 hay 4 x 6 n 8 x 12cm. Mt cch t l lp kim loi nhm (Al) tinh khit (99,999 %) v dy t 0,2 - 0,5 mm. Lp kim loi ny c a ln b bng con ng in phn c bit trong mi trng tr. Mt lp kim loi nhn bng v c khc ln nhiu vch song song v cch u nhau. S vch c khc ln lp kim loi ny thng l t 650 - 3600 vch/mm. S vch trn 1 mm cng nhiu th kh nng phn li nh sng ca cch t cng ln.62Nh th, nu chng ta chiu mt chm sng song song khng n sc vo mt cch t theo mt gc ti a no th ch c vch trn cch t nh mt chn sng, ch khng c vch nh mt khe sng v di tc dng ca hin tng nhiu x trn b mt cch t th chm sng a sc s c phn li thnh ph. Nu gi p l gc l ca tia sng, di sng l X th ta lun lun c biu thc:sina + swinp = m.k.X(3.29)Biu thc ny c gi l cng thc c bn ca cch t. Cng thc ny gii thch cho ta nguyn nhn s tn sc ca cch t, v t cng thc (3.29) ta c:sinp = m.k.X + sina(3.30) y a l gc ti ca chm sng, m v k l khng i i vi mt cch t. Nn ng vi mi bc sng X ta s c mt gi tr sinp tc l c 1 gi tr p. iu c ngha l cch t phn li chm sng a sc thnh tng tia n sc lch i theo tng gc 13 khc nhau. Nhng y sng di b lch nhiu, cn sng ngn b lch t hn. ng thi cch t cho ta ph c nhiu bc, ng vi cc gi tr m ca cng mt di sng X S m c gi l bc ca ph cch t.Nu tia ti vung gc vi mt cch t, tc l gc ti a - 0 th cng thc (3.30) s c dng l:sinp = m.k.X(3.31)Trong trng hp ny gc phn x ca cc tia sng khng ph thuc vo gc ti a m ch ph thuc vo hng s k ca cch t v di sng ca tia sng m thi. Trong thc t ngi ta hay t cch t v tr ny trong my quang ph.Nu gc ti a= 13 th cng thc (3.30) s l:sinp = (mk/2).X(3.32)y chnh l tia sng X c gc ti a tc dng ng vo gia knh nh ca mt vng ph ca hp nh. V th cng thc ny c s dng tnhgc ti a khichnvng ph cho mt php phn tch. cng l v tr cc tiu ca tiasng trungtnmcavng ph cn chn trong my.Mt khc, cng chnh do hin tng nhiu x qua khe hp to ra ph ca cch t cho nn khong cch t v tr cc i cc vn sng n tnm hnh nhiu x c tnh theo cng thc:xt = m.f0.(X/k)(3.33)ngha l:Cc i th 1 cch tnm mt on xt1 = (1.f2,X)/kCc i th 2 cch tnm mt on xt2 = (2.f2.X )/k63Cc i th 3 cch tnm mt on xt3 = (3.f2)/kCc i th m cch tnm mt on xtm = (m.f2)/k.iu ny gii thch cho ta ti sao tn sc di ca cch t bc th m gp m ln bc th 1, ngha l c tn sc bc th m l:Ddm = (3.34)mVi m l s nguyn v m > 1.My quang ph cch tMy quang ph cch t, v nguyn tc, cng c cu to nh my quang ph lng knh. Nhng y h tn sc l mt cch t, v cng dng ba i lng c trng nh trong my quang ph lng knh nh gi cht lng ca mt my quang ph cch t. C th l: tn sc gcT cng thc c bn ca cch t (3.29), nu xt s bin thin ca gc lch p theo di sng X th ta c:cosp.dp = (m.k).dXhay l:Dg = Dr800

Cu-324,754Eu-324,753>254

Fe-271,903Pt-271,904>054

Pr-411,848Fe-411,854>050

Mn-403,307Ga-403,298>025

Zn-213,856Fe-213,850>200

4.2.1:3 S bc x ca cc ht rnTrong mi trng pht x, c bit l trong ngn la n kh, h quang, nhiu khi cn c cha c cc ht rn rt nh li ti ca vt cht mu cha b ha hi v nguyn t ha, hay cc ht mui cacbon ca nhin liu cha c t chy hon ton. Cc ht loi ny thng c lp v ca ngn la v n cng b kch thch pht x ra ph nn, do cng gy kh khn cho vic quan st hay o cng vch ph phn tch. Yu t ny th hin rt r khi chn khng ng chiu cao ca n nguyn t ha mu v cc iu kin ca ngun kch thch ph khng ph hp.Cc yu t vt lThuc v loi yu t vt l ny thng c: nht v sc cng b mt ca dung dch muTrong php o ICP-AES, hay vi k thut nguyn t ha mu trong ngn la, nu mu l dung dch, yu t ny nh hng nhiu n tc dn mu vo bung aerosol ha v hiu sut aerosol ha ca mu v t m nh hng n kt qu phn tch. Ni chung, tc dn ng chun phi c cng nng axit, loi axit v thnh phn ha hc, vt l ca tt c cc nguyn t khc, nht l cht nn ca mu. Yu t ny thng th hin nhiu trong php o AES dng ngun ngn la v h quang in. loi tr nh hng ny chng ta c th dng cc bin php sau y:Chnh s khc nhau v nng axit, loi axit, nng cht nn ca mu, thnh phn ca cc cht c trong dung dch mu, nguyn nhn gy ra khc nhau v nht ca dung dch mu. V th trong mi qu trnh phn tch mt nguyn t, nht thit phi m bo sao cho mu phn tch v cc mu u lpmu t l nghch vi nht ca dung dch mu (hnh 4.2)..77o v xc nh theophng php thm tiuchun, Pha long mubng mt dung mi haymt nn ph hp,Thm vo mu chtm c nng ln,Dng bm ymu vi mt tc xcnh m chng ta mongmun.S Ion ha ca cht phn tchNu o vch ph trung ha ca nguyn t, y l yu t vt l th ba nh hng n kt qu phn tch, v qu trnh Ion ha lm gim s nguyn t t do ca nguyn t phn tch, do lm gim cng vch ph pht x ca nguyn t trung ha, khi nguyn t phn tch b Ion ha cng nhiu. Nhng mc b Ion ha ca mi nguyn t l khc nhau, v ph thuc vo nhit ca mi trng pht x. Trong mt iu kin nht nh, ni chung cc nguyn t c th Ion ha cng thp th cng b Ion ha nhiu. Vi mt nguyn t, khi nhit ca mi trng pht x cng cao th nguyn t cng b Ion ha nhiu hn. Bng 4.2 l mt v d v iu ny.Bng 4.2Mc Ion ha ca mt s nguyn tN.tTh Ion ha(eV)S % b Ion ha nhit (oC):

200030004000

Na5,2100,3005,0026,00

K4,3202,1022,0082,00

Rb4,1609,0034,0090,00

Cs3,8728,0070,0096,00

Mg7,5400,1200,5005,60

Ca6,1100,2001,5015,00

Sr5,6900,5002,3518,70

Ba5,3101,0006,0023,00

F(ml/ph)

TI246810Hnh 4.2nh hng ca nht n tc dn mu78Nhng nu o vch ph Ion th yu t ny li l cn thit v ta phi chn iu kin qu trnh Ion ha t hiu sut cao v n nh nht, c c nng ln ca nguyn t cn xc nh (phn tch) cao nht.Thc t cho thy rng, qu trnh Ion ha thng ch c ngha i vi cc kim loi kim v sau l cc kim loi kim th, cn i vi cc nguyn t khc s Ion ha l khng ng k trong mi trng ca ngn la n kh v h quang in. loi tr s Ion ha mt nguyn t phn tch chng ta c th dng cc bin php sau y:+ Chn iu kin nguyn t ha c nhit thp, m trong iu kin nguyn t phn tch hu nh khng b Ion ha.+ Thm vo mu phn tch mt cht m cho s Ion ha. l cc mui halogen ca cc kim loi kim c th Ion ha thp hn th Ion ha ca nguyn t phn tch vi mt nng ln ph hp. Nh vy trong iu kin nguyn t phn tch s khng b Ion ha na.Hin tng t o (t hp th) ca vch phngHin tng ny thng xut hin trong vng ngoi ca plasma l r rt nht hay khi nng cht phn tch ln. V vng ny c nhit thp, nn cc nguyn t ca cht phn tch li hp th chnh tia pht x m cc nguyn t trong li ca ngn la sinh ra, v th lm mt bt i mt phn cng pht x ca cht phn tch. iu ny cng gp phn gii thch ti sao nng ln th mi quan h gia cng vch ph pht x I^v nng Cx ca cht l khng cn tuyn tnh na.Trn y l mt s yu t vt l c th xut hin trong php o AES v c th nh hng n kt qu phn tch. Nhng mc xy ra l rt khc nhau trong mi trng hp c th, c khi c, c khi khng. Mc ny xut hin ln hay nh ph thuc vo:+ Nhit ca plasma,+ Cc iu kin ca mi trng kch thch ph pht x,+ Tnh cht ca nguyn t phn tch v hp cht ca n,+ Cht nn ca mu v thnh phn ca mu phn tch.Do cn phi xem xt tm bin php loi tr khi chng xut hin, theo tng loi mu c th.Cc yu t ha hcTrong php o ph pht x nguyn t cc nh hng ha hc cng rt a dng v phc tp. N xut hin cng rt khc nhau trong mi trng hp c th v cng nhiu trng hp khng xut hin. Cc nh hng ha hc thng c th dn n kt qu79theo bn hng sau y:Lm gim cng ca vch ph ca nguyn t phn tch, do s to thnh cc hp cht bn nhit, kh ha hi v kh nguyn t ha. V d nh nh hng ca cc Ion silicat, sunfat, photphat, florua. Lm tng cng ca vch ph, do s to thnh cc hp cht d ha hi v d nguyn t ha, hay do hn ch c nh hng ca s Ion ha ca nguyn t phn tch. chnh l tc dng ca mt s hp cht, ch yu l mui halogen ca kim loi kim v kim th hay lantan Clorua.S tng cng vch ph khi nguyn t phn tch tn ti trong nn ca mu l nhng hp cht d ha hi. Lc cc cht nn ny c tc dng nh l mt cht mang cho s ha hi ca nguyn t phn tch v lm n c ha hi vi hiu sut cao hn. S gim cng ca vch ph khi nguyn t phn tch tn ti trong nn mu l nhng hp cht bn nhit, kh ha hi. Lc ny cc nguyn t nn km hm s ha hi ca nguyn t phn tch. Cc cht nn ny thng l nhng hp cht bn nhit ca cc nguyn t, nh Al, t him, silicat, v.v...V th vic nghin cu cc nh hng ha hc c trnh by trong chng ny c tnh cht khi qut chung tt c cc loi c th c chng ta lu khi ng dng php o ph pht x nguyn t, vi mc ch bit v loi tr cc nh hng ha hc, nu chng xut hin. Cc nh hng ha hc c th c sp xp theo cc loi sau y:Nng axit v loi axit trong dung dch muNi chung nng axit trong dung dch mu lun lun c nh hng n cng ca vch ph ca nguyn t phn tch v nh hng ny thng gn lin vi loi Anion ca axit. Cc axit cng kh bay hi thng cng lm gim nhiu cng vch ph. Ngc li, cc axit d bay hi gy nh hng nh (hnh 4.3). iu ny c th thy r rng khi xc nh Ca o vch ph Ca-422,7 nm trong cc mi trng ca cc axit HClO4, CH3COOH, HCl, HNO3, H2SO4, H3PO4, HF vi cng mt nng l 2% (hnh 4.4).Ni chung, cc axit lm gim cng vch ph theo th t: HClO4 < HCl < HNO3 < H2SO4 < H3PO4 < HF, ngha l axit HClO4, HCl v HNO3 gy nh hng nh nht. Chnh v th trong thc t phn tch ca php o ph pht x nguyn t (AES) ngi ta thng dng mi trng l axit HCl hai HNO3 1 hay 2%, v nng ny nh hng ca hai axit ny l khng ng k (nh hn 5%).80

Hnh 4.4nh hng ca loi axit n cng vch ph.V d vch ph Ca - 422,7 nm trong php o F - AES (khng kh + C2H2)v nh hng ca cc Cation khc trong muDung dch mu phn tch, ngoi nguyn t cn xc nh, cn cha cc nguyn t khc. Cc nguyn t ny tn ti di dng cc Cation hay Anion tan trong dung dch81mu. Cc Ion ny c th lm tng, cng c th lm gim, hoc cng c th khng gy nh hng g n cng vch ph ca nguyn t phn tch. Khi c nh hng th mc nhhngcamiIon cng rtkhc nhau trongtngtrnghpcth.Nhng mt cch tng qut th chng ta c th quy nh hng ca cc Cation theo 7 loi nh trong hnh 4.5 d xem xt.Loi 1, khi nng ca Ion gy nh hng ln hn C2 th n khng lm tng cng vch ph ca nguyn t phn tch na, nh hng ny c s dng tng nhy ca phng php phn tch mt nguyn t, khi thm vo mu nguyn t nh hng c nng ln hn C2 (xem ng 1, hnh 4.5).Loi 2, th ti nng Cl ca nguyn t gy nh hng cng vch ph ca nguyn t phn tch t gi tr cc i. V th nh hng ny cng c dng tng nhy ca phng php phn tch. Nhng phi gi (khng ch) nng ca nguyn t gy nh hng gi tr khng i Cl (ng 2, hnh 4.5).Loi 3. Trong trng hp ny cng vch ph gim lin tc theo ng cong li khi nng nguyn t nh hng tng dn u (ng 3 trong hnh 4.5).Loi 4. Cc Cation ch gy nh hng n cng vch ph ca nguyn t phn tch khi nng ca n ln hn gi tr C4. Do vy, nu nng ca cc Cation trong mu nh hn gi tr C4 th khng phi quan tnm n tm bin php loi tr (ng 4, hnh 4.5).Loi 5. Trong trng hp ny cng vch ph ca nguyn t phn tch li b gim lin tc theo ng cong lm, khi nng Cation gy nh hng trong dung dch mu tng dn v y nht thit phi tm bin php loi tr nh hng ny (ng 5, hnh 4.5).Loi 6. Khi nng ca cc Cation khc trong mu ln hn gi tr C5 th chng khng lm gim cng vch ph ca nguyn t phn tch. Do nu khng tm c bin php loi tr ph hp, th chng ta thm vo mu Cation gy nh hng vi nng ln hn gi tr C6, a nh hng gim thnh mt gi tr hng s cho tt c cc mu phn tch v mu chun. Nh th cng loi b c nh hng ny. Nhng tt nhin l ta lm gim nhy ca phng php phn tch i mt t.Loi 7. y cc Cation l lm gim lin tc cng vch ph ca nguyn t phn tch theo chiu tng dn nng ca n mt cch tuyn tnh (ng 7, hnh 4.5). Do cng cn phi tm bin php ph hp loi tr nh hng ny, hoc gi cho cc Cation l c nng nht nh v khng i trong tt c cc mu chun v cc mu phn tch.nh hng ca cc Cation c trong mu n cng vch ph ca nguyn t phn tch trong php o ph nguyn t cng rt khc nhau. V d: Ion La(III) trong php o F-AAS l yu t loi tr nh hng ca cc Ion l c trong mu khi xc nh Ca, Mg, Mn, Al, Fe. Nhng chnh La(III) li l Ion nh hng v lm gim cng82 vch ph ca chnh Ca, Mg, Al, Fe rt ln trong php o F-AES. iu c ngha l mi Cation trong tng trng hp c th v trong mi php li c tc dng khc nhau, m chnh n trong php o ny th nh hng, nhng trong php o khc li khng gy nh hng.Nh vy, nh hng ca cc Cation n cng vch ph ca nguyn t phn tch c th c hiu ng dng, hiu ng nm v cng c th c hiu ng va nm va tng i vi mt Ion, khi n cc nng khc nhau. minh ho v nh hng ca cc Cation i vi vch ph ca nguyn t phn tch chng ta c th xem xt mt s v d trong cc hnh t 4.6 - 4.8.h

Hnh 4.5Khi qut v nh hng cc ion kim loi loi tr nh hng ca cc Cation n cng vch ph ca nguyn t phn tch chng ta c th s dng mt s bin php sau y hoc ring bit, hoc t hp ca chng vi nhau, ty tng trng hp c th, v d c th:+ Thm cht ph gia kh nh hng;+ Thay i nn ca mu loi tr nh hng;+ Pha long mu bng cht ph gia lm gim thiu nh hng,+ Thay i iu kin ha hi, nguyn t ha v kch thch ph;83+ Thay i mi trng kh quyn kch thch ph, dng kh tr argon, v.v.

81216202428HEIGHT ABOVE LOAD COIL (mmlHnh 4.6nh hng ca chiu cao o n cng vch ph Nguyn t phn tch: (A) - Fe, (B) - Ca, v (C) -AI

200400ng/mL.Hlnh 4.7nh hng ca T n Ba (1), Sr(2), v Ca (3) (nh hng loi 6)84

nh hng ca cc AnionCng vi cc Cation, cc Anion cng nh hng n cng vch ph ca nguyn t phn tch, v nh hng ny cng tng t nh nh hng ca cc loi axit. Ni chung, cc Anion ca cc axit d bay hi thng lm gim t cng vch ph. Ch ring c hai Anion ClO- 4 v CH 3CPPOO-, l gy hiu ng dng (lm tng), tc l lm tng cng vch ph ca nguyn t phn tch trong mt s trng hp mt85vng nng nht nh. Cc Anion khc thng gy hiu ng nm (lm gim) theo th t Cl-,ON3,CO3,SO4,PO4,SiO3. Trong Anion SiO3c nh hng ln nht, cn tnht l hai Ion Cl- v NO-3. ng thi khi nng ca cc Anion tng th tc dng nh hng cng tng theo (hnh 4.9). Do thc t nn trong mi php o phi gi cho nng ca cc Anion trong mu phn tch v mu chun l nh nhau v mt gi tr nht nh khng i. Mt khc, cng khng nn chn axit H2SO4 lm mi trng ca mu cho php o AES m ch nn dng axit HCl hay HNO3 vi nng di 2%.crBr'no; so^PO^Caii0,20,4%Hnh 4.9Khi qut v nh hng ca cc anionThnh phn nn ca muYu t nh hng ny ngi ta quen gi l matrix effect. Nhng khng phi lc no n cng xut hin, m ch thy trong mt s trng hp nht nh. Thng thng l cc mu c cha cc nguyn t nn di dng cc hp cht bn nhit, kh bay hi v kh nguyn t ha. V d: Khi xc nh cc tp cht lng vt trong cc mu oxit t him, oxit kim loi kim th, oxit nhm, oxit zircon, cc mu mui NaCl, th cc nn ny s kh cng ca vch ph ca nguyn t phn tch; qua lm gim nhy ca phng php phn tch. Trong nhiu trng hp, yu t ny lm gim hng chc ln, thm ch c trng hp lm gim hng trm ln cng ca vch ph (bng 4.4). Nguyn nhn chnh ca nh hng ny l s tn ti ca cc hp cht bn nhit trong mi trng pht x. Cc hp cht ny lm kh khn, cn tr qu trnh ha hi v nguyn t ha ca cc nguyn t phn tch. loi tr nh hng ca thnh phn nn ca mu phn tch ngi ta c th dng cc bin php khc nhau, nh:86

Tng nhit ca plasma kch thch ph;Thm vo mu cc cht ph gia c nng ph hp;Thay i nn ca mu sang nn khc;Tch loi b nguyn t nn cn tr, khi ba bin php trn khng t kt qu. Tt nhin bin php ny l hn hu.Bng 4.4nh hng ca thnh phn nn ca mu phn tchCht nn ca muCng vch ph C=30 ppb php o AES

Mg-202,60 nmCa-422,70 nm

1. Dung dch HCl 1%0,2200,250

2. Nh 1, thm 2% LaCl30,0080,005

3. Nh 1, thm 0,5% LaCl30,0500,060

3. Nh 2, thm 1% NH4NO3+LiBO20,2100,245

Trong cc bin php trn, bin php th nht cng ch thc hin c trong nhng chng mc nht nh, v chng ta khng th tng nhit nguyn t ha ln cao mi c, do s hn ch ca trang thit b, bn cht ca khi t, hn na khi nhit nguyn t ha qu cao th li xut hin nh hng ca s Ion ha. Cho nn bin php hai v ba l thng dng nht. Cc cht ph gia thng hay c dng trong php o F-AES, ICP-AES l LaCl3, SrCl2, LiCl, KCl, AlCl3 v cht ph gia c dng nhiu nht l LiBO2, NH4NO3 hay hn hp ca hai cht ny vi mt nng ph hp.87Chng 5PHN TCH QUANG PH PHT X NH TNHNguyn tc chungNh chng ta bit, khi cung cp nng lng ha hi, nguyn t ha mu phn tch v kch thch m hi nguyn t i n pht x th chng ta s thu c ph pht x ca mu phn tch. Ph gm ba thnh phn:Ph vch ca nguyn t v Ion.Ph m ca phn t v nhm phn t.Ph nn lin tc.Trong ba thnh phn , th ph vch l thnh phn chnh c trng cho nguyn t v Ion trng thi hi t do, khi chng b kch thch, ngha l trng thi hi. Khi b kch thch, cc nguyn t v Ion s pht ra mt chm bc x quang hc gm nhiu tia c bc sng khc nhau nm trong di ph quang hc (190-1100nm). Nu thu, phn li v ghi chm sng li ta s c mt di ph gm cc vch pht x ca nguyn t v Ion ca cc nguyn t c trong mu. Trong tp hp cc vch ph , th mi loi nguyn t hay Ion li c mt s vch c trng ring cho n. Cc vch ph c gi l cc vch ph pht x c trng ca loi nguyn t y. V d khi b kch thch: Nguyn t Al pht ra vch c trng trong vng UV: 308,215; 309,271nm. Nguyn t Cu pht ra vch c trng trong vng UV: 324,754; 327,396nm. - M pht ra vch c trng trong vng UV: 259,373; 260,570nm.Nguyn t m pht ra vch c trng trong vng UV:279,553; 280,270nm.Chnh nh cc vch ph c trng ny ngi ta c th nhn bit c s c mt hay vng mt ca mt nguyn t no trong mu phn tch qua vic quan st ph pht x ca mu phn tch, v tm xem c cc vch ph c trng ca n hay khng, ngha l da vo cc vch ph pht x c trng ca tng nguyn t nhn bit chng. l nguyn tc ca phng php phn tch quang ph pht x inh tnh.T c s vt l chng ta c th khi qut qu trnh phn tch quang ph pht x nh tnh gm cc giai on sau y:Cung cp nng lng ha hi, nguyn t ha mu phn tch to ra m hi nguyn t t do v kch thch m hi pht ra ph pht x ca chng.Thu chm sng pht x , phn li v ghi ph pht x ca mu phn tch.Quan st ph thu c ca mu phn tch theo cc vch c trng ca cc88nguyn t pht hin chng.Cc giai on ny c thc hin nh mt h thng my quang ph pht x. H thng my ny cng gm ba phn chnh tng ng vi ba nhim v nu trn. l:Phn 1.Ngunnnglng ha hi,nguyntha v kch thchmhinguyn t ca mu n pht x.Phn 2. My quang ph thu, phn li v ghi ph pht x ca mu.Phn 3. H thng trang b quan st nh tnh v nh lng.Trong phn tch nh tnh, khi quan st khng thy vch ph pht x c trng ca mt nguyn t trong ph ca mu phn tch, iu c th xy ra hai kh nng: 1hoc l hon ton thc t khng c nguyn t trong mu phn tch, 2. Hoc l nguyn t c trong mu phn tch, nhng nng ca n nh hn nhy pht hin ca phng php phn tch. V th khng xut hin vch ph pht x c trng ca n. V d: Nu dng 2 loi ngun HQ v ICP kch thch ph pht x th:+ Vi ngun HQ: 2 vch Cu nu trn xut hin nng C > 0,0004%+VingunICP:Cng2vchCu ny,nhngxuthinnng C >00004%. Do vic kt lun kt qu phn tch phi theo phng php phn tch v cc iu kin trang b dng thu ghi ph ca mu phn tch v nhy ca phng php s dng. l hin tng thc t, song ngi ta thng hay quy c v coi nh l khng c nguyn t trong mu phn tch, khi khng tm c cc vch c trng (2 vch ph) ca nguyn t trong ph pht x ca mu phn tch, theo k thut dng nh tnh.Vch chng minh nh tnh v cch chnMun xc nhn s c mt hay khng c mt ca mt nguyn t no trong mu phn tch, ngi ta phi tm mt s vch ph c trng ca nguyn t trong ph ca mu phn tch xem c hay khng, t m kt lun c n hay khng c n trong mu phn tch. Nhng vch ph c trng c chn c gi l vch chng minh ca nguyn t y. Ni chung, pht hin mt nguyn t t kt qu chnh xc v chc chn, ngi ta phi chn t nht hai vch chng minh khi quan st ph ca mu phn tch. Cc vch ph ny phi tha mn mt s iu kin sau y: Nhng vch ph ny phi r rng v khng trng ln vi cc vch ca nguyn t khc, nht l nguyn t nng ln.N phi l nhng vch ph nhy, c th pht hin c cc nguyn t trong mu vi nng nh (phn tch lng vt).Vicchnccvchphchng minh chomtnguyntphixutphttngun nng lng dng kch thch ph ca mu phn tch, v trong ngun kch89thch c nng lng thpthphcanguyn t lchyu vvch nguyntcanthng l nhng vch nhy. Ngc li, trong ngun kch thch giu nng lng (ICP) th ph ca Ion l ch yu. Cho nn phi ty thuc vo ngun nng lng dng kch thch ph m chn vch chng minh l vch nguyn t hay vch Ion cho ph hp.Phi cn c vo my quang ph c th thu, phn li v ghi c trong vng sng no m chn vch chng minh cho mt nguyn t nht nh. V d chng minh Na, nu ph mu c ghi trn my Q-24 (vng ph 200-400 no th ta phi chn hai vch Na 330,30 v Na 330,27 nm. Ngc li, nu ghi trn my lng knh thy tinh (vng ph 360-780 nm.), th li phi chn hai vch Na 589,60 v 589,00 nm.Nudng my cch t PGS-2 (vng ph 200- 1100 nm) th chn 4 vch trn u c. nhy ph v kh nng pht hinTrong phn tch quang ph pht x nguyn t ngi ta thng s dng hai khi nim v nhy. l nhy tuyt i v nhy tng i xem xt hay nh gi kh nng phn tch ca mt phng php. nhy tuyt i (cn gi l nhy khi lng) nhy tuyt i l lng gam nh nht ca mt nguyn t cn phi a vo kch thch ph trong plasma cn pht hin c t nht hai vch ph c trng ca nguyn t y trong mt iu kin nht nh chn, ngha l cn chng minh c nguyn t y. V d, ch c th pht hin c cc nguyn t:+ Pb khi trong plasma h quang kch thch ph phi c 0,000007 g Pb.+ Al khi trong plasma h quang kch thch ph phi c 0,0000055 g Al.Cn cc gi tr nh hn th khng th pht hin c Pb v Al. Cc gi tr (lng gam) 0,000007 g v 0,0000055 g c gi l nhy tuyt i ca Pb v Al trong php phn tch . Nh vy, mi nguyn t khc nhau c nhy tuyt i khc nhau v ph thuc vo mi nguyn t, cc iu kin kch thch v ghi ph ca mu (bng 5.1). nhy tng i (cn gi l nhy nng ) nhy tng i l nng nh nht ca mt nguyn t phi c trong mu phn tch cn c th pht hin c t nht hai vch ph c trng ca n, trong cc iu kin thc nghim nht nh chn. Cn nu nh hn nng th ta khng th tm c mt vch c trng no ca n trong ph ca mu phn tch. V d: pht hin c hai vch ph c trng ca cc nguyn t sau trong ngun h quang, phi c:90+ Pb vi nng trong mu l => 0,0008 %+ Al vi nng trong mu l => 0,0004 %+ Cu vi nng trong mu l => 0,0005 %Cc gi tr 0,0008; 0,0004; 0,0005 % c gi l nhy tng i ca Pb, Al v Cu trong php phn tch ny. l nng nh nht cn pht hin c cc nguyn t theo 2 vch ph pht x ca n trong mt iu kin nht nh chn .Cng nh khi nim trn, mi nguyn t khc nhaucng c nhytngikhc nhau. Ni chung, cc nguyn t c t vch ph thngc nhy cao (bng 5.1).Trong phn tchngi ta hay dng khinimnhytngiv chikhicnthit mi dng khi nim nhy tuyt i, v dng khi nim nhy nng chng ta d so snh nhy ca cc nguyn t vi nhau hn. Nh vy, kh nng chng minh ca mt nguyn t ph thuc vo nhy ph ca nguyn t . Nguyn t no cng nhy ph th cng c th pht hin c n ngay nng rt nh (tt nhin l nng ny phi cn ln hn nhy tng i).Ngoi nhy ph ca mt nguyn t, kh nng chng minh ca nguyn t cn ph thuc vo mt s yu t khc, nh:+ Cc iu kin thc nghim ha hi, nguyn t ha mu, kch thch cc nguyn t v iu kin trang b ghi o ph ca mu phn tch.+ Cht lng ca h thng quang hc ca my quang ph;+ Cu to, thnh phn vt l v ha hc ca mu phn tch;+ Mi trng kch thch ph;+ Trng thi tn ti ca nguyn t trong mu;+ Cht ph gia thm vo mu phn tch.Nhng trong mt iu kin th nghim nht nh ph hp c chn, vi h thng trang b nh nhau v cng mt loi mu, th kh nng chng minh ca mt nguyn t ch cn ph thuc vo nhy ph ca nguyn t phn tch v trang b thu nhn ph m thi.V th mun nh gi, so snh kh nng chng minh ca mt nguyn t bng ph pht x nguyn t, chng ta phi nghin cu chng trong nhng iu kin nht nh nh nhau v ph hp, nh ngun nng lng ha hi, nguyn t ha v kch thch ph, cng nh cc iu kin ghi ph ca chng.Bng 5.191Vch c trng ca mt s nguyn tNguyn tVch ph (nm)Cng Nng xut hin (%)

I 328,0685500R0,0001

AgI 338,2892800R0,0006

I 520,907100R0,02

I 546,549100R0,025

I 257,51048R0,08

I 308,216320R0,001

Al

I 309,271650R0,0005

I 396,153900R0,0003

I 249,678420R0,005

Ba

I 249,773480R0,003

II 233,52755R0,02

Ba

II 234,75816R0,05

II 455,4046500R0,0005

II 493,4092000R0,001

II 553,555650R0,006

II 315,887200,05

II 317,933500,02

CaII 393,3674420R0,0005

II 396,8472200R0,001

II 422,6731100R0,003

I 2824,34500,05

I 3247,545000R0,0004

Cu

I 3273,962500R0,001

I 5105,54400,06

I 248,328280rh0,001

I 259,9412000,003

FeI 302,065280R0,001

I 358,120600R0,0005

I 371,994700R0,00045

I 373,448700r0,0005

92S trng vch v cch loi trPh pht x ca mt nguyn t thng c rt nhiu vch, c khi n hng ngn vch. Cc vch ny phn b t vng sng ngn n sng di ca di ph quang hc (190-1100 nm). Nguyn t no c cu to lp v in t cng phc tp, nht l s in t ha tr cng nhiu, th ph pht x ca chng cng c nhiu vch, v d nh Fe. V th, ph pht x ca mu phn tch, nht l cc mu a kim loi, th ph pht x ca n tt nhin cng c nhiu vch. Trong di ph tt nhin c th c hai nguyn t khc nhau, nhng chng li c th pht ra tia bc x cng di sng, hoc khc nhau khng n 0,01 nm. Trong trng hp ny vch ph ca hai nguyn t l trng nhau hon ton hoc l chng ln nhau mt phn, ngha l c hin tng trng vch, hin tng quy ri v chen ln ca cc vch ph ca cc nguyn t vi nhau.Vch ph trngVch ph trng l cc vch ph ca cc nguyn t khc nhau, nhng c cng mt gi tr di sng. V th trn knh nh ta ch thy c mt vch duy nht. V d vch La 412,323nm trng vi vch ph Er 412,823nm (khng nhy). Nn khi nh tnh khng c chn vch La 412,323nm chng minh nguyn t La, mc du l mt vch nhy ca La.Vch quy ri v chen lnVch quy ri v chen ln l vch ph ca cc nguyn t khc nhau, nhng chng c i sng xp x bng nhau m my quang ph khng phn gii c thnh cc vch ring r. V th trn knh nh hai vch ph ny nm k nhau v c mt phn chng ln nhau. Do khi quan st ta cng ch thy c mt vch rng. Song c trng hp hai vch c th tch ra c nng nh ca c hai nguyn t, nhng khi mt trong hai nguyn t c nng ln, tt nhin l vch ca nguyn t c nng ln s ln t vch ca nguyn t c nng nh. l s quy ri v chen ln ca cc vch ph ca cc nguyn t. V th, chng minh nh tnh mt nguyn t chng ta cng phi loi tr nhng vch ph c hin tng .Ph mBn cnh s trng vch v s quy ri ca cc vch ph ca cc nguyn t khc nhau, th ph m ca cc phn t v nhm phn t cng l mt yu t gy kh khn cho php phn tch nh tnh, v trong nhiu trng hp th ph m ca cc phn t che lp mt cc vch c trng ca cc nguyn t khc. iu ny th hin rt r trong vng kh kin (380-780 nm), nu ta kch thch ph ca mu phn tch trong mi trng khng kh, hay trong cc my quang ph c phn gii khng ln. l nhng kh nng c th xy ra khi quan st bt k mt bng vch ph no ca cc nguyn t ha hc. Song khng phi v th m khng chng minh nh tnh c mt nguyn t theo ph pht x ca n. Bng thc t, ngy nay ngi ta c rt