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Lecture 8

CHEM 212 Lecture Notes - Lecture 8: Analyte, Dont, Analytical ChemistryPremium

2 pages54 viewsFall 2016

Department
Chemistry
Course Code
CHEM 212
Professor
Hamilton M.Coreen
Lecture
8

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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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