PLEASE TURN CELL PHONES OFF!!CHM 4130: Instrumental Analysis Spring 2018 3 Credits Time/Day: TR, 12:30-1:45 pm Location: OE 134 Instructor: Dr. Yi Xiao Office: CP 306 Office hours: Tues: 3-4 pm and Thurs: 3-4 pm E-mail: [email protected] Principles Of Instrumental Analysis 6th Edition By Skoog, Holler, Crouch REQUIREDGrading policy CHM 4130: • Two regular exams = 60% Total three regular exams will be given (You can drop one of the three regular exams) • Final exam = 40% Homework Will be assigned for each chapter, and will not be collected, but some of them will put on Exams.n About Analytical Chemistry 1. Qualitative analysis Identify and classify the analyte 2. Quantitative analysis Determine the amount or concentration of the analyten Classification of Analytical Methods n Classical methods (wet chemical methods) n Instrumental methodsComparisons of Wet Chemical and Instrumental Methods Wet chemical Instrumental Separation methods Precipitation Extraction Distillation Chromatographic Electrophoretic Quantitative methods Gravimetric Volumeric Conductivity Electrode potential; light absorption, emission Mass/charge ratio (M/Z) fluorescencen Types of Instrumental Methods (energy source stimulus vs. analyte response). n Separation techniques n Chromatography n Gas n Liquid n Electrophoresis n Many types n Detection techniques n Electrochemistry n Optical spectroscopy n Absorption n Emission n Fluorescence n Mass spectroscopy n Atomic n MolecularData domains – various modes of encoding information n Non-electrical domains: n Length, pressure, density, light intensity, number etc… n Electrical domains: n Analog domain n Time domain n Digital domain Non-electrical => transducer => electrical =>Non-electricalElectrical Data domains: n Analog-Domain = Magnitude of Voltage, current, charge, or power(potential problems with electric noise!)Electrical Data domains: n Time-Domain = frequency, pulse width, phase, etc…Digital domain: n Digital-Domain = counts, serial, number, etc…n Instruments for Analysis Energy Source Sample Analytical Signal Input Transducer (Detector) Signal Processor Output Transducer (Readout)Interdomain Conversion Non-electrical <=> Electrical <=>Non-electricaln Instruments for Analysisn Interdomain Conversionsn Interdomain Conversions Nonelectrical information → electrical signal → nonelectrical signaln Selection of an Instrumental Method n Defining the problem n Accuracy required n Sample availability n Concentration range of analyte n Matrix effects/interferences => selectivity! n How many samples? n Performance characteristics n Precision n Sensitivity n Detection limit n Dynamic range n Selectivityn Precision A measure of the random or indeterminate error of an analysis – reproducibility of datan Bias A measure of the systematic or determinate error of an analytical method Bias = µ - Xt µ - the population mean for the concentration of an analyte Xt – true concentration One or more standard reference materials (SRM) are commonly used to determine the analytical bias! Eliminate or correct for bias by the use of blanks and by instrument calibration.n Sensitivity A measure of the ability of an analytical method to discriminate between small differences in analyte concentration. 1. The slope of the calibration curve 2. The reproducibility or precision of the measuring device Sbl Signal Concentration x x x x Concentration Sbl Signal x x x x A B Blank!n Sensitivity n Calibration sensitivity m (S = mc + Sbl) n Analytical sensitivity (γ = m/sS) m – slope sS – standard deviation of the measurement Relative insensitive to amplification factors Signal Concentration Increase the gain of the instrument by a Factor of twon Detection limit (Limit of detection, LOD) The analyte concentration giving a signal equal the blank signal, Sbl, plus three times the standards deviation of the blank, sbl Mean blank signal Standard deviation of the Blank signal Sm = Sbl + ksbl Analytical Signal Using m to convert signal response, Sm, to analyte concentration Cm k = 3 !!!!n Dynamic Range Range from lowest concentration (LOQ, limit of quantitative) to the concentration where the calibration curve departure from linearity (limit of linearity, LOL) Blank signal Standard deviation of the Blank signal Sm = Sbl + ksbl Analytical Signal Convert signal response, Sm, to analyte concentration k = 10 !!!n Dynamic Range Non-ideal detector resp. - a deviation of 5% from linearity 10 x blankn Guideline for Reporting Data (ACS recommended) Analyte Concentration Region of reliability < 3σ Region of Questionable detection (unacceptable) 3σ Detection limit 3σ-10σ Region of less certain quantitation 10σ Limit of quantitation > 10σ Region of quantitation< 3σ 3σ 3σ-10σ 10σ > 10σn Selectivity The degree to which the method is free from interference by other species contained in the sample matrix S = mAcA + mBcB + mCcC + Sbl m = calibration sensitivity; c = analyte concentration The selectivity coefficient for B with respect to A kB,A = mB/mA …………………………………… Note: this is the selectivity of an analytical detection techniquen Calibration Methods-1 n Comparison with Standard n Direct comparison Ø Colorimetric i.e comparative color scale. n Titration (often below required sensitivity)n Calibration Methods-2 n External Standard Calibration method: n Ideal when no matrix effects are present n Correct for blanks- calibrate instruments and procedures n Prepare calibration curve n Indetermined errors => non-ideal & curve fit required Signal Concentration X X X X Normally use the method of least squares fitn Calibration Methods-2 n External Calibration Curve Two Assumptions for the method of least squares: 1. Linear relationship – y = mx + b 2. deviation of the individual points from the straight line arises from the error in the measurementn Calibration