CHEM 212 Lecture 8: Sept. 23/2016
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Department
Chemistry
Course Code
CHEM 212
Professor
Hamilton M.Coreen

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Chem 212!
Lecture 8!
Sept. 23/2016!
!
External Standard --> Calibration Curve!1.
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 original (undiluted) sample --> this is unknown!
-Cs= [analyte] in spiking solution before adding to sample!
!
""100 mL Sample
!! 100mL vol. for both
!!!!!!!2 mL Std
!20 mL sample!!!!!20 mL sample
Ca*20mL/100mL]--> Ss!! [Ca*20mL/100mL + 2mL Cs/100mL] --> Ss+s

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Description
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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