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Analytical Chemistry II

303354. Analytical Chemistry II. Somsak Sirichai. Lectures: Tuesday 1.00-3.00 p.m. Friday 8.00-9.00 a.m. C310. Course Description:. Teach fundamental of instrumentation analysis. Spectrochemical analysis. UV-VIS, IR, Fluorescence & Phosphorescence,

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Analytical Chemistry II

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  1. 303354 Analytical Chemistry II Somsak Sirichai Lectures: Tuesday 1.00-3.00 p.m. Friday 8.00-9.00 a.m. C310

  2. Course Description: Teach fundamental of instrumentation analysis • Spectrochemical analysis UV-VIS, IR, Fluorescence & Phosphorescence, AA, ICP, X-ray, NMR, MS • Electrochemical analysis Potentiometry, Coulometry, Voltammetry • Chromatographic analysis GC, HPLC • Capillary Electrophoresis CZE

  3. Gradings • 2 exams (mid-term, final each worth 40%) • Quizzes (10%) • Paper (10%) <40%  F Texts: Skoog & Leary, Principles of Instrumental Analysis* Weston & Brown, HPLC and CE Khaledi; High Performance Capillary Electrophoresis

  4. Qualitative analysis (1) Quantitative analysis (2) Analysis Introduction (1) A type of chemical analysis by which the analyte or analytes in a sample are identified. (2) A type of chemical analysis by which the amount of each analyte or analytes in a sample is determined.

  5. analyte(s) the species to be determinded in the sample matrix Matrix-analyte = concomitants

  6. Classification of Analytical Methods 1. Classical methods Qualitative– identification by color, indicators, boiling or melting points, odors Quantitative – mass or volume (e.g. gravimetric, volumetric)

  7. 2. Instrumental methods 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.

  8. Signal Example Method Types of Instrumental Methods Radiation emission Emission spectroscopy (X-ray, UV, visible), fluorescence, phosphorescence, luminescence Radiation absorption Absorption spectroscopy spectrophotometry, photometry, NMR electron spin resonance

  9. Signal Example Method Radiation Scattering Raman spectroscopy Radiation refraction Refractometry Radiation diffraction X-ray and Electron diffraction method Radiation rotation Polarimetry Electrical potential Potentiometry

  10. Signal Example Method Electrical charge Coulometry Electrical current Voltammetry – amperometry polarography Electrical resistance Conductometry Mass Gravimetry Mass-to-charge ratio Mass spectrometry Rate of reaction Flow injection analysis

  11. Analytes (in matrix) Energy stimulus Analytical response Data Instruments for Analysis Encoded information Example: Spectrophotometry Instrument: spectrophotometer Stimulus: monochromatic light energy Analytical response: photocell Data: electrical current Data processor: current meter Readout: meter scale

  12. Encoded information: detector : device that indicates changes in environment transducer : device that converts non-electrical to electrical data Non-electrical domians Electrical domains Physical Current (light intensity, colour) Chemical (pH) Voltage

  13. Selecting an Analytical Method Defining the Problem A definition requires answers to the following questions: • What accuracy and precision are required? • How much sample is available? • What is the concentration range of the analyte? • What components of the sample will cause • interference? • What are the physical and chemical properties • of the sample matrix? • 6. How many samples are to be analysed?

  14. Performance Characteristics of Instruments; Figures of Merit Precision: Indeterminate or random errors • Absolute standard deviation (s) • Relative standard deviation (RSD) • Variance (s2) • Coefficient of variation (a percentage) • (CV) • Standard deviation of means (sm)

  15. Absolute standard Deviation (s) Relative standard deviation (RSD) Coefficient of Variation (CV) Standard deviation of means (sm)

  16. Accuracy: determinate errors (operator, method, instrumental) % Relative error (%Er)

  17. Sensitivity: “the ability to detect (qualitative analysis) or determine (quantitative analysis) small amounts of an analyte in a sample” x = analytical signal C = the analyte concentration Sensitivity : slope of calibration curve (Larger slope of calibration curve, more sensitive measurement)

  18. Limit of detection (LOD): “the lowest concentration of analyte in a sample that can be detected”

  19. Limit of Quantitation (LOQ) “the minimum injected amount that produces quantative measurements in the target with acceptable precision”

  20. Selectivity: “ability of the method to measure one species of analyte in the presence of other elements or compounds” Example: Signal = mACA + mBCB + Signalblank A + B mA, mB = calibration sensitivity of A, B CA, CB = concentration of A, B sample Selectivity coefficient: kB,A = mB/mA k’s vary between 0 (no selectivity) and large number (very selective).

  21. Calibration methods Basis of quantitative analysis is magnitude of measured property is proportional to concentration of analyte” Signal  [x] or Signal = m[x] + signalblank [x] = (signal-signalblank)/m

  22. Calibration curve (working or analytical curves) Dynamic Range Instrument response (signal) LOQ LOD LOL Slope m Signalblank [x]

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