Chemistry 155 Introduction to Instrumental Analytical Chemistry

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Chem 155 Unit 1 Page 42 of 3137. How to plan a set of standard preparations in theMS Excel spreadsheet program:Calibration Standard Preparation:Target Conc: Stock Conc: Final Volume: Volume to Pipet:C2 / ppt C1 / ppt V2 / mL V1=C2*V2/C11.00 100.0 10.00 0.100 mL2.00 100.0 10.00 0.200 mL5.00 100.0 10.00 0.500 mL10.00 100.0 10.00 1.000 mL15.00 100.0 10.00 1.500 mLCalibration StandTarget Conc: Stock Conc: Final Volume: Volume to Pipet:C2 / ppt C1 / ppt V2 / mL V1=C2*V2/C11 100 10 =A4*C4/B4 mL2 100 10 =A5*C5/B5 mL5 100 10 =A6*C6/B6 mL10 100 10 =A7*C7/B7 mL15 100 10 =A8*C8/B8 mLThese are formulas that you type intoExcel – normally only the result of theformula calculation is displayed.Page 42 of 313
Chem 155 Unit 1 Page 43 of 3131.11 Validation – Assurance of Accuracy:Calibration and linear regression optimizes theprecision of a calibration curve determination but acalibration curve can only be said to be accurate if:the analysis has been validatedAnother way of saying this is that a method is valid if:all significant sources of biashave been removedValidation addresses the various aspects of ananalysis that can ‘go wrong’ and give you a wronganswer.The table below lists some of the aspects of ananalysis that can be invalid, and suggests ways tovalidate them.Source of bias:Analyst erraticError in analysttechniqueCalibrationstandards are inerror (are not whatthey say the are)CalibrationmethodInstrumentfunction erraticInstrument driftPossible Solution(s):Analyst can repeat experimentDifferent analyst does same analysis andgets same result.Entire analysis Independent standardrepeated with measured periodically -indpendent called validation standardcalibration or QC standard (qualitystandard set control)Different calibration method used (standardadditions)Different instrument used (can be a differentkind of instrument)Periodically measure validation standard orinternal standardPage 43 of 313
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Chemistry 155 Introduction to Instrumental Analytical Chemistry

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