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### Introduction

Yongsik Lee

Classification of Analytical Methods

- Classical methods
- Instrumental methods

Instrumental Methods

- Photon
- Charge
- Heat
- Radioactive

Instruments

- Data domain
- Non-electrical domain
- Electrical domain
- Analog
- Time
- digital

Detectors

- Detectors
- 물리량의 변화를 기록 또는 표시
- 기계적, 전기적, 화학적 장치

- Transducers
- 비전기적 영역 정보와 전기적 영역 정보 사이 변환
- 변환 함수 = 둘 사이의 수학적 관계식

- Sensors
- 특정 화학종을 연속적으로, 가역적으로 검출하는 분석장치

Other Components of Instrument

- Readout device
- Microprocessor
- Computer

Selecting a method

- Defining the problem
- 요구되는 정확도
- 이용할 수 있는 시료의 양
- 분석물의 농도 범위
- 방해 성분
- 시료 매트릭스의 물리적, 화학적 성질
- 시료의 개수
- 신속성
- 실험자의 숙련도
- 기기 장치의 가격과 이용 가능성
- 시료당 비용

Characteristics of Instrument

- Precision
- Bias
- Sensitivity
- Detection limit
- Concentration range
- selectivity

Precision

- 정밀도
- Measure of random, or indeterminate error
- 재현성 reproducibility
- 표준편차, 변동계수 등
- 표 1-5 성능 계수 (figure of merit)

Bias

- 고정 오차
- Measure of systematic or determinate error

- Definition
- Bias = (population mean) – (true value)

Sensitivity

- Definition
- Measure of its ability to discriminate between small differences in analyte concentration
- Tow factors
- Slope of calibration curve - steeper slope
- Precision – better precision

Classification of Analytical Methods

- Qualitative instrumental analysis
- measured property indicates presence of analyte in matrix

- Quantitative instrumental analysis
- magnitude of measured property is proportional to concentration of analyte in matrix

- Classical
- Qualitative - identification by color, indicators, boiling points, odors
- Quantitative - mass or volume
- e.g. gravimetric, volumetric

- Instrumental
- Qualitative - chromatography, electrophoresis and identification by measuring physical property
- e.g. spectroscopy, electrode potential

- Quantitative
- measuring property and determining relationship to concentration
- e.g. spectrophotometry, mass spectrometry
- Often, same instrumental method used for qualitative and quantitative analysis

Types of Instrumental Methods:

- Radiation emission
- Emission spectroscopy - fluorescence, phosphorescence, luminescence

- Radiation absorption
- Absorption spectroscopy - spectrophotometry, photometry, nuclear magnetic resonance, electron spin resonance

- Radiation scattering
- Turbidity, Raman

- Radiation refraction
- Refractometry, interferometry

- Radiation diffraction X-ray, electron

- Radiation rotation
- Polarimetry, circular dichroism

- Electrical potential
- Potentiometry

- Electrical charge
- Coulometry

- Electrical current
- Voltammetry - amperometry, polarography

- Electrical resistance
- Conductometry

- Mass
- Gravimetry

- Mass-to-charge ratio
- Mass spectrometry

- Rate of reaction
- Stopped flow, flow injection analysis

- Thermal
- Thermal gravimetry, calorimetry

- Radioactivity
- Activation, isotope dilution
- (Often combined with chromatographic or electrophoretic methods)

Example: Spectrophotometry

- Instrument: spectrophotometer
- Stimulus: monochromatic light energy
- Analytical response: light absorption
- Transducer: photocell
- Data: electrical current
- Data processor: current meter
- Readout: meter scale

Data Domains

- way of encoding analytical response in electrical or non-electrical signals
- 정보를 코드화하는 여러 방법들을 영역(도메인)이라고 한다
- Interdomain conversions transform information from one domain to another.
- Light Intensity => Photocell Current => Current Meter Scale
- Detector (general): device that indicates change in environment
- Transducer (specific): device that converts non-electrical to electrical data
- Sensor (specific): device that converts chemical to electrical data

Non-Electrical Domains

- Physical (light intensity, color)
- Chemical (pH)
- Scale Position (length)
- Number (objects)

Electrical Domains

- Current
- Voltage
- Charge
- Frequency
- Pulse width
- Phase
- Count
- Serial
- Parallel

Time Domains

- 정보는 신호의 크기로서 보다는 시간에 따른 신호의 요동으로 시간 영역에 저장된다.
- Time
- vary with time
- frequency, phase, pulse width

- Analog
- continuously variable magnitude
- current, voltage, charge

- Digital
- discrete values
- count, serial, parallel, number

Digital Binary Data

- Advantages
- easy to store
- not susceptible to noise

Figures of Merit

- Performance Characteristics:
- How to choose an analytical method?
- How good is measurement?
- How reproducible? - Precision
- How close to true value? - Accuracy/Bias
- How small a difference can be measured? - Sensitivity
- What range of amounts? - Dynamic Range
- How much interference? - Selectivity

Precision

- Indeterminate or random errors
- Absolute standard deviation
- 절대표준편차

- Variance 분산 : s2
- Relative standard deviation:
- 상대 표준편차
- RSD = s/<x>

- Standard deviation of mean:
- 평균의 표준편차
- sm

Accuracy Sensitivity

- Determinate errors (operator, method, instrumental)
- Bias:
- bias = <x> - x(true)

- Calibration sensitivity: S
- larger slope of calibration curve means more sensitive measurement

Analytical Sensitivity

- Mandel and Stiehler
- 분석감도 = 검정곡선기울기/측정표준편차
- 기기의 증폭률을 증가시키면 검정곡선 기울기는 증가하지만, 일반적으로 측정 표준편차도 같이 증가하므로 분석감도는 일정하다.

Detection Limit

- Signal must be bigger than random noise of blank
- Minimum signal:
- Signal min = Average Signal of blank + ks(blank)
- From statistics k=3 or more
- (at 95% confidence level)
- Suggested by Long and Winefordner

Dynamic Range

- At detection limit we can say confidently analyte is present but cannot perform reliable quantitation
- Level(Limit) of quantitation (LOQ): (k=10)s(blank)
- 정량적 측정을 할 수 있는 가장 낮은 농도, 정량 한계

- Limit of linearity (LOL)
- when signal is no longer proportional to concentration, 선형 한계

- Dynamic range 유용한 측정농도 범위

Selectivity:

- No analytical method is completely free from interference by concomitants. Best method is more sensitive to analyte than interfering species (interferent).
- Matrix with species A&B
- Signal = mAcA +mBcB + Signal blank

- Selectivity coefficient
- kB,A = mB/mA

- k's vary between 0 (no selectivity) and large number (very selective).

Calibration methods

- 검정
- Basis of quantitative analysis is magnitude of measured property is proportional to concentration of analyte
- Signal ∝ µ[x]
- Signal = m[x]+ Signal of blank

- [x] = {Signal -Signal of blank}/m

Standard Addition Method

- spiking
- 같은 크기의 시료 분취량에
- 표준물 용액 일정량을 증가시키며 더하고 측정

- 매트릭스는 표준물 첨가후에도 거의 변화없다고 가정
- 최소제곱분석법

Internal Standard Method

- 내부 표준
- 모든 시료, 바탕, 그리고 분석 표준물에 일정량씩 더하는 물질

- 검정곡선 획득
- 신호비=표준 분석물의 신호/내부 표준물의 신호
- 신호비를 표준물의 농도에 대해 그려 얻는다.

- 우연오차와 계통오차를 보정할 수 있다
- 적당한 내부표준물 확보가 어렵다

Species of interest

- All constituents
- including analyte.
- Matrix-analyte
- =concomitants
- Often need pretreatment - chemical extraction, distillation, separation, precipitation

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