Chapter 1: Introduction Analytical Chemistry Analytical Chemistry Qualitative analysis Qualitative analysis Quantitative analysis Quantitative analysis Classification of Analytical Methods Classification of Analytical Methods Classical methods (wet chemical methods) Classical methods (wet chemical methods) Instrumental methods Instrumental methods

Comparisons of Wet Chemical and Instrumental Methods Wet chemicalInstrumental Separation methods Precipitation Extraction Distillation Chromatographic eletrophoretic Detection methods Colors Boiling or melting points Solubilities Odors Conductivity Electrode potential\light absorption, emission Mass/charge ratio (M/Z) fluorescence

Types of Instrumental Methods Types of Instrumental Methods Separation techniques Separation techniques Chromatographic Chromatographic Gas Gas Liquid Liquid ……. ……. Electrophoresis Electrophoresis Many types Many types Detection techniques Detection techniques Optical spectroscopy Optical spectroscopy Absorption Absorption Emission Emission Fluorescence Fluorescence Mass spectroscopy Mass spectroscopy Atomic Atomic Molecular Molecular

Instruments for Analysis Instruments for Analysis Signal Generator Sample Analytical Signal Input Transducer (Detector) Signal Processor Output Transducer (Readout)

Instruments for Analysis Instruments for Analysis

Selection of An Instrumental Method Selection of An Instrumental Method Defining the problem Defining the problem Performance characteristics Performance characteristics Figure of Merits: Quantitative performance criteria of instruments that are expressed in numerical terms

Precision Precision A measure of the random or indeterminate error Relative Standard Deviation

Bias Bias A measure of the systematic or determinate error Bias = µ - X t µ - the population mean for the concentration of an analyte X t – true concentration Standard reference materials (SRM)

Sensitivity Sensitivity A measure of the ability of an analytical method to discriminate between small differences in analyte concentration Calibration sensitivity (S = mc + S bl ) Calibration sensitivity (S = mc + S bl ) S bl Signal Concentration x x x x S bl Signal xx xx

Sensitivity Sensitivity Analytical sensitivity (  = m/s S ) Analytical sensitivity (  = m/s S ) m – slope; s S – standard deviation of the measurement Relative insensitive to amplification factors Signal Concentration Increase the gain of the instrument by a Factor of two

Detection limit (Limit of detection, LOD) Detection limit (Limit of detection, LOD) The analyte concentration giving a signal equal the blank signal, S bl, plus three time standards deviation of the blank, s bl Blank signal Standard deviation of the Blank signal S m = S bl + ks bl Analytical Signal S m, Convert signal response, S m, to analyte concentration

Dynamic Range Dynamic Range Lowest concentration (LOQ) to the concentration where the calibration curve departure from linearity (limit of linearity, LOL) Blank signal Standard deviation of the Blank signal S m = S bl + ks bl Analytical Signal S m, Convert signal response, S m, to analyte concentration

Dynamic Range Dynamic Range

Guideline for Reporting Data (Recommended by ACS Committee of Environmental Improvement) Guideline for Reporting Data (Recommended by ACS Committee of Environmental Improvement)Analyte ConcentrationRegion of reliability < 3σRegion of Questionable detection (unacceptable) 3σDetection limit 3σ-10σRegion of less certain quantitation 10σLimit of quantitation > 10σRegion of quantitation

99.7% Question: When the value of 10 s bl (standard deviation of the blank) is used as LOQ, what is the relative standard deviation of the measurement at this point at the 99.7% confidential level, and why?

Selectivity Selectivity The degree to which the method is free from interference by other species contained in the sample matrix S = m A c A + m B c B + m C c C + S bl The selectivity coefficient for B with respect to A k B,A = m B /m A …………………………………… Note: this is the selectivity of an analytical detection technique

Calibration Methods Calibration Methods Analytical response Comparison with Standard Comparison with Standard Direct comparison Direct comparison  Colorimetric Titration Titration Analyte Concentration

Calibration Methods Calibration Methods External Calibration Curve External Calibration Curve Signal Concentration X X X X Normally use the method of least squares

Calibration Methods Calibration Methods External Calibration Curve External Calibration Curve Two Assumptions: 1. Linear relationship 2. deviation of the individual point from the straight line arises from the error in the measurement

Calibration Methods Calibration Methods Standard Addition Standard Addition Signal Concentration Without sample matrix effect With sample matrix effect (signal suppressed)

Standard Addition Standard Addition Signal Concentration C0C0 C1C1 C2C2 C3C3 x x x x Conc. of analyte C 0 Sample signal S bl C 1, C 2, and C 3 are the concentrations of analyte after spiked with stnard, with counting the amount of analyte in the original sample solution. C 0 is the concentrations of analyte in sample without spiking S = mC + S bl C 0 =S bl /m

Internal Standard Internal Standard Add a substance in a constant amount to all samples and, blanks, and calibration standard in an analysis Concentration S analyte /S internal