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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

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Introduction

Introduction

Yongsik Lee


Classification of analytical methods
Classification of Analytical Methods

  • Classical methods

  • Instrumental methods


Instrumental methods
Instrumental Methods

  • Photon

  • Charge

  • Heat

  • Radioactive


Instruments
Instruments

  • Data domain

    • Non-electrical domain

    • Electrical domain

      • Analog

      • Time

      • digital


Detectors
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
Other Components of Instrument

  • Readout device

  • Microprocessor

  • Computer


Selecting a method
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
Characteristics of Instrument

  • Precision

  • Bias

  • Sensitivity

  • Detection limit

  • Concentration range

  • selectivity


Precision
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
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 methods1
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
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
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
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
Non-Electrical Domains

  • Physical (light intensity, color)

  • Chemical (pH)

  • Scale Position (length)

  • Number (objects)


Electrical domains
Electrical Domains

  • Current

  • Voltage

  • Charge

  • Frequency

  • Pulse width

  • Phase

  • Count

  • Serial

  • Parallel


Time domains
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
Digital Binary Data

  • Advantages

    • easy to store

    • not susceptible to noise


Figures of merit
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


Precision1
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
Accuracy

  • Determinate errors (operator, method, instrumental)

  • Bias:

    • bias = <x> - x(true)

  • Sensitivity

    • Calibration sensitivity: S

    • larger slope of calibration curve means more sensitive measurement


  • Analytical sensitivity
    Analytical Sensitivity

    • Mandel and Stiehler

    • 분석감도 = 검정곡선기울기/측정표준편차

    • 기기의 증폭률을 증가시키면 검정곡선 기울기는 증가하지만, 일반적으로 측정 표준편차도 같이 증가하므로 분석감도는 일정하다.


    Detection limit
    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
    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
    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
    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
    Standard Addition Method

    • spiking

      • 같은 크기의 시료 분취량에

      • 표준물 용액 일정량을 증가시키며 더하고 측정

    • 매트릭스는 표준물 첨가후에도 거의 변화없다고 가정

    • 최소제곱분석법


    Internal standard method
    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
    Species of interest

    • All constituents

    • including analyte.

    • Matrix-analyte

    • =concomitants

    • Often need pretreatment - chemical extraction, distillation, separation, precipitation


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