Atomic absorption spectrometry was used with the method of standard additions to
ID: 786839 • Letter: A
Question
Atomic absorption spectrometry was used with the method of standard additions to determine the concentration of cadmium in a sample of an industrial waste stream. For the addition, 10.0 ?L of a 1000.0 ?g/mL Cd standard was added to 10.0 mL of solution. The following data were obtained: Absorbance of reagent blank = 0.046 Absorbance of sample = 0.328 Absorbance of sample plus addition = 0.898. What was the concentration of the cadmium in the waste stream sample? _____ ug/mL Later, the analyst learned that the blank was not truly a reagent blank, but water. The absorbance of the actual reagent blank, was 0.10. Calculate the cadmium concentration using the new information of the blank. _____ ug/mL Calculate the percent error caused by using water instead of the reagent blank. _____ %Explanation / Answer
for 10 ul of 1000 ug/ml
then for 10 ml = say 'X'
X = 10 x 1000000 [as 1 ml = 1000 microlitres]
X = 10^7 microg/ml is the concentration of Cadmium in waste stream sample.
AS per newly blank value i.e 0.10 and absorbance of sample = 0.328
the conc of cadmium can be calc as
Amt of cd = [ sample - Blank ] x concentaion of cd in waste stream / Wt or volume taken
= [ 0.328 - 0.10 ] x 10^7 / 10
= 0.228 x 10^6
= 228000 micro g/ml (or) 228 mg/ml
Percentage error caused is = ( abs of reagent blank / abs of water ) x 100
= ( 0.046 / 0.10 ) x 100 = 0.46 x 100 = 46 %
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