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Lecture 8

CHEM 212 Lecture 8: Sept. 23/2016

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University of Victoria
CHEM 212
Hamilton M.Coreen

Chem 212 Lecture 8 Sept. 23/2016 1. External Standard --> Calibration Curve 2. Internal Standard--> F 3. Standard Addition has two methods: a) Constant Final Volume /Standard addition to multiple solutions (intercept for result) b) Varying final volume or standard addition to a single solution *single point by either a or b is a ratio Varying Final volume technique-Std addition to a single solution: -plot on X-axis: volume of standard after dilution [Cs]*(Vstd/Vo) Cs= standard solution concentration Vo=initial volume of sample -Plot on Y-axis: Signal(sample+spike)*(Vf/Vo) Vf= volume of sample +spike intercept at y=0 gives - [unknown sample] Practical ways around standard addition: -Very labour intensive to carry out addition experiment --> don't do this -Usually do single point std addition 1) constant final volume 2) varying final volume -calculations done by ratios not plotting graphs -DONT DO SUBTRACTIONS of results Clues for choosing which method is being used: nothing added to sample in case 1 --> External standard similar compound added in case 2--> Internal Standard analyte added in case 3 --> Standard Addition--> Ratio Concentration of analyte in initial solution____________ signal from initial solution Concentration of analyte plus standard in final solution signal from final solution Ss=k[As] Ss+s=k([A]+[S]) Proportionality constants cancel when divided, so we don't have to worry about it: ___Ss=k[As]___ Ss+s=k([A]+[S]) Data Needed: -Ca= [analyte]in origin
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