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Introduction

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

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  1. Introduction Yongsik Lee

  2. Classification of Analytical Methods • Classical methods • Instrumental methods

  3. Instrumental Methods • Photon • Charge • Heat • Radioactive

  4. Instruments • Data domain • Non-electrical domain • Electrical domain • Analog • Time • digital

  5. 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

  6. Other Components of Instrument • Readout device • Microprocessor • Computer

  7. 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

  8. Characteristics of Instrument • Precision • Bias • Sensitivity • Detection limit • Concentration range • selectivity

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

  10. Bias • 고정 오차 • Measure of systematic or determinate error • Definition • Bias = (population mean) – (true value)

  11. 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

  12. 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

  13. 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

  14. 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

  15. Radiation rotation • Polarimetry, circular dichroism • Electrical potential • Potentiometry • Electrical charge • Coulometry • Electrical current • Voltammetry - amperometry, polarography • Electrical resistance • Conductometry

  16. 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)

  17. Example: Spectrophotometry • Instrument: spectrophotometer • Stimulus: monochromatic light energy • Analytical response: light absorption • Transducer: photocell • Data: electrical current • Data processor: current meter • Readout: meter scale

  18. 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

  19. Non-Electrical Domains • Physical (light intensity, color) • Chemical (pH) • Scale Position (length) • Number (objects)

  20. Electrical Domains • Current • Voltage • Charge • Frequency • Pulse width • Phase • Count • Serial • Parallel

  21. 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

  22. Digital Binary Data • Advantages • easy to store • not susceptible to noise

  23. 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

  24. 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

  25. Accuracy • Determinate errors (operator, method, instrumental) • Bias: • bias = <x> - x(true) • Sensitivity • Calibration sensitivity: S • larger slope of calibration curve means more sensitive measurement

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

  27. 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

  28. 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

  29. 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).

  30. 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

  31. Standard Addition Method • spiking • 같은 크기의 시료 분취량에 • 표준물 용액 일정량을 증가시키며 더하고 측정 • 매트릭스는 표준물 첨가후에도 거의 변화없다고 가정 • 최소제곱분석법

  32. 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

  33. Calibration curves (working or analytical curves)

  34. Example

  35. Calculate Precision

  36. Calibration Expression

  37. Species of interest • All constituents • including analyte. • Matrix-analyte • =concomitants • Often need pretreatment - chemical extraction, distillation, separation, precipitation

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