FIU CHM 4130 - CHAPTER 1_Xiao_Introduction_2018 (38 pages)

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CHAPTER 1_Xiao_Introduction_2018



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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 yxiao2 fiu edu Textbook Principles Of Instrumental Analysis 6th Edition By Skoog Holler Crouch REQUIRED Grading 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 analyte n Classification of Analytical Methods Classical methods wet chemical methods n Instrumental methods n Comparisons 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 fluorescence n Types of Instrumental Methods energy source stimulus vs analyte response n Separation techniques n Chromatography n n n Electrophoresis n n Gas Liquid Many types Detection techniques n n Electrochemistry Optical spectroscopy n n n n Absorption Emission Fluorescence Mass spectroscopy n n Atomic Molecular Data domains various modes of encoding information n Non electrical domains n n Length pressure density light intensity number etc Electrical domains Analog domain n Time domain n Digital domain n Non electrical transducer electrical Non electrical Electrical 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 electrical n Instruments for Analysis n Interdomain Conversions n Interdomain Conversions Nonelectrical information electrical signal nonelectrical signal n Selection of an Instrumental Method n Defining the problem Accuracy required n Sample availability n Concentration range of analyte n Matrix effects interferences selectivity n How many samples n n Performance characteristics Precision n Sensitivity n Detection limit n Dynamic range n Selectivity n n Precision A measure of the random or indeterminate error of an analysis reproducibility of data n Bias A measure of the systematic or determinate error of an analytical method Bias Xt 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 The reproducibility or precision of the measuring device 2 Signal Signal A B x x x x x x Concentration x x Sbl Sbl Concentration Blank n Sensitivity Calibration sensitivity m S mc Sbl n Analytical sensitivity m sS n m slope sS standard deviation of the measurement Relative insensitive to amplification factors Signal Increase the gain of the instrument by a Factor of two Concentration n 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 Sm Sbl ksbl Analytical Signal Mean blank signal k 3 Standard deviation of the Blank signal Using m to convert signal response Sm to analyte concentration Cm 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 Sm Sbl ksbl Analytical Signal Blank signal k 10 Standard deviation of the Blank signal Convert signal response Sm to analyte concentration n Dynamic Range 10 x blank Non ideal detector resp a deviation of 5 from linearity n Guideline for Reporting Data ACS recommended Analyte Concentration 3 3 3 10 10 10 Region of reliability Region of Questionable detection unacceptable Detection limit Region of less certain quantitation Limit of quantitation Region of quantitation 10 3 3 10 3 10 n 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 technique n Calibration Methods 1 n Comparison with Standard n Direct comparison n Colorimetric i e comparative color scale Titration often below required sensitivity n Calibration Methods 2 n External Standard Calibration method n n n n Ideal when no matrix effects are present Correct for blanks calibrate instruments and procedures Prepare calibration curve Indetermined errors non ideal curve fit required Signal X X X X Concentration Normally use the method of least squares fit n 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 measurement n Calibration Methods 3 n Internal Standard Calibration method n n n n Add a substance in a constant amount to all samples and blanks and calibration standard in an analysis Response factors determined through calibration curve Signal of IS needs to be similar to analytes but distinguishable IS needs to be absent in original sample Sanalyte SIS Analyte concentration of the standard n Calibration Methods 4 n Standard Addition method Needed to address matrix effects Signal Without sample matrix effect With sample matrix effect signal suppressed Concentration n Standard Addition method 1 Transfer aliquots of the unknown solution Vx of unknown concentration Cx to volumetric flasks of volume Vt 2 Add variable volumes Vs of standard analyte solution of concentration Cs 3 Dilute all to volume Vt and determine analyte signal S blank corrected 4 Prepare standard addition calibration curve by plotting Vs vs S S


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