Introduction to Instrumental Analysis in Chemistry

2017년, 기기분석

• 전체 분석과정에 포함된 여러 단계 ;

1) Sampling

bulk material로 부터 시료의 제조 -분쇄, 혼합,건조,등

2) Preparation of solutions

- 시료의 종류, 분석 목적에 따라.

3) Separation

- 측정 성분 또는 방해 성분의 분리

4) Measurement

- 기기와 방법에 따라 2,3 과정 차이

5) Report (the most important)

*** 한 성분의 정량을 위해 여러 가지 방법이 가능

---분석 목적에 맞는 적합한 방법의 선택이 필요.

고려되어야 할 사항 ; speed, convenience,

accuracy, availability of equipment,

number of analyses,

amount of sample,

concentration of the analyte, etc.

Principles of Instrumental Analysis by Douglas A. Skoog et al. Analytical chemistry deals with methods for determining the chemical composition or samples or matter. -Qualitative ; information about the atomic or molecular species or functional groups.

- Quantitative ; numerical information as to the relative amount or one or more or the components.

1A Classification of Analytical Methods

1A-1. Classical methods: 1) Qualitative:

① colors ② bp. or mp. ③ solubility in solvents

④ odors ⑤ activities, ⑥ refractive index, etc.. 2) Quantitative: gravimetric & volumetric 1A-2. Instrumental Methods - Measurements of physical properties of analytes:

conductivity, electrode potential, absorption or emission of light,

mass-to-charge ratio, fluorescence, chromatography, etc..

*기기분석: 물리적, 물리화학적 방법을 이용한 화학저울보다 일반적으로 복잡하고 값비싼 기재를 이용하여 분석 1860년 : Cs, Rb 발견 - 불꽃 광도법 시험 1927년 polarography 1940,41년: Beckmann사에서 flame photometer 상품화 ………… Advantages : 1) selectivity 大 2) 시간단축 3) 조작용이, 개인차 小 4) sensitivity 大 5) 자동화, 연속화 가능 6) 비파괴 분석 가능 Disadvantages: 1) 표준물질, 2) 분석치의 유효숫자 小 3) 기기가격 大 4)보수유지 난이

1B. Types of Instrumental Methods i ) Spectroscopy

ii) Electrochemistry

iii) Chromatography

iv) Mass spectrometry

v) Thermal methods

vi) Radioactivity

vii) Rate of reaction

viii) Microscopy

i) Spectroscopy a) Emission of radiation

--- Emission spectroscopy ( X-ray, UV-Visible, Electron, Auger)

--- Fluorescence and phosphorescence spectroscopy (X-ray,UV-Visible)

--- Radiochemistry

b) Absorption of radiation

--- Spectrophotometry ( X-ray, UV, visible, IR )

--- Photoacoustic spectroscopy

--- Nuclear magnetic resonance and Electron spin resonance spectroscopy

c) Scattering of radiation

--- Tubidimetry

--- Nephelometry

--- Raman spectroscopy

d) Refraction of radiation

--- Refractometry

--- Interferometry

e) Diffraction of radiation

--- X-ray and Electron diffraction methods

f) Rotation of radiation

--- Polarimetry

--- Optical rotatory dispersion

--- Circular dichroism

ii) Electrochemical a) Electrical potential

--- Potentiometry

--- Chronopotentiometry

b) Electrical current

--- Polarography ( normal - differential pulse, classical…)

--- Amperometry (cyclic voltammetry, strriping voltammetry, chrono-…)

c) Electrical resistance

--- Conductometry

--- Oscillometry

iii) Chromatography a) Liquid chromatography

--- Liquid - liquid (LLC)

--- Liquid - solid (LSC)

--- Liquid - bonded phase (LSB)

--- Ion - exchange (IEC)

--- Gel - permeation (GPC)

b) Gas chromatography

--- Gas - liquid (GLC)

--- Gas - solid (GSC)

--- Gas - bonded phase

c) Electrophoresis

iv) Other methods a) Mass spectrometry

b) Thermal methods ; TG, DSC, DTA, etc.

c) Mass; gravimetry (quartz crystal microbalance)

*** See Figure: Components of a typical instrument***

v) Rate of reaction ; Kinetic methods

vi) Radioactivity ; Activation & isotope dilution methods

1C. Instruments for Analysis

Data-domain map: Nonelectrical & Electrical

1C-1 Data Domains

1C-2 Nonelectrical domain : ex) characteristic properties of emission of radiation

1C-3 Electrical Domains Analog – Domain Signals: These are continous in both amplitude and time. Time – Domain information: As the time relationship of signal fluctuation Digital information: information can be represented by the state of a light bulb, a light-emitting diode, a toggle switch, or a logic-level signal

Figure 1-3 Diagram of a fluorometer

Diagram for digital data

1C- 4 Detectors, Transducers and Sensors Instrument components: Signal generator, Analytical input, Electrical generator, Signal transduce or Signal output or Mechanical process, Signal detector. A. Signal generator ex) pH변화, 기체의 열전도율, 불꽃세기의 강도, 용액에 흡수되는 광선의 강도 -energy source, optical system B. Detectors (input Transducers) A transduce is a device that converts one of energy to an other.

i.e thermocouple, a photocell, the beam or a balance.

detector : transducers that act on a chemical signal.

analytical signal - electrical voltage or current

ex) 광전지, 광전관, 유리전극

Detectors: a mechanical, electrical, or chemical device that identifies, records, or indicates a change in one of the variables in its environment (P, T, Q, hv, etc). Transducers: The devices that convert information in nonelectrical domains to information in electrical domains and the converse. Sensors: The class of anlytical devices that are capable of monitoring specific chemical species continuosley and reversiblely.

Chemical sensors

C. Circuits - output signal ex) 1) converting circuit : 전류 - 전압, 직류 - 교류 2) amplifying circuit : 필요한 수준까지 충족 3) computing circuit : 표준과 비교, 미분, 적분.. 4) assistant circuit : wave generation 5) power supply circuit : 위의 회로 동작을 위한 전원 D. Readout Devices (output의 표시) ex) Analog meter: Digital meter, Oscilloscope,Recorder E. Microprocessors and computers in instruments - op amp. IC, A/D and D/A converters counters, microprocessor, and computers.

분석기기의 성능판정 (신뢰성, 측정방식)

A 기기의 신뢰성 1) 타당성 - 감응도, 감동 , 응답 2) 정확도 - bias가 적은편 3) 정밀도 - dispersing 이 적은편 D-1. Comparison with standards Direct Comparison: color comparison,… Titrations: S.R. in a reaction of known stoichiometry D-2. External–Standard Calibration: The Least –Squares Method, Errors in External-Standard Calibration, Multivariate calibration D-3. Standard-Addition Methods

1D Calibration of Instrumental Methods

The uncertainties are related to the residual.

Errors in External-Standard Calibration The raw analytical response is corrected by measuring a blank.

- A solvent blank - A reagent blank

Blank corrections

Systematic errors can occur during the calibration process.

Random errors

Contamination of the standards can also result in higher analyte concentrations than expected.

mbyc c

x−

= ( )xx

cyc

Syy

NMmSS 2

2

m11 −++=bmxy +=

Calibration plot for the standard addition method

S = kVsCs/Vt + kVxCx/ Vt , m = kCs/Vt , b=kVxCx/Vt , b/m = VxCx/Cs

Standard Addition Methods

Plot of S as a function of Vs

1-E2 Performance characteristics of instruments A) precision - absolute standard deviation - relation standard deviation - standard deviation of to mean - coefficient of variation - variance

B) Bias Bias = µ - Ƭ (µ: population mean, Ƭ: true value)

C) Sensitivity 1) Calibration sensitivity: the slop of calibration curve S = mc + Sbl, Cx=(Yc-b)/m s : the measured signal c : the concentration of the analyte Sbl : the instrumental signal for a blank m : the slop of the strait line 2) Analytical sensitivity ; Ɣ = m/ss

ss = the standard deviation of the signal

D) Detection Limit → The a minimum concentration or weight of analyte that can be detected at a known confidence level. - mean blank signal Sm = Avg(Sbl) + kSbl Sm – Avg(Sbl) Def. of DL: Cm = ------------------- m Sm: minimal distinguishable analyte signal

E) Applicable concentration range The limit of quantitative measurements is taken as being signal to ten times the

standard deviation when the analyte concentration is zero. (LOQ & LOL)

F) Selectivity A: analytes, B & C S: mAcA + mBcB + mCcC+ Sbl

KB,A = mB/mA : Selectivity coefficient for A with respect to B KC,A = mC/mA

Signal = mA (cA + kB,A cB + kC,A cC) + Sbl