Atomic absorption spectrometry was used with the method of standard additions to
ID: 887381 • 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 = 0.043 Absorbance of sample = 0.434 Absorbance of sample plus addition = 0.890 What was the concentration of the cadmium in the waste stream sample?
Later, the analyst learned that the blank was not truly a reagent blank, but water. The absorbance of the actual reagent blank, was 0.090. Calculate the cadmium concentration using the new information of the blank.
Calculate the percent error caused by using water instead of the reagent blank.
Explanation / Answer
absorbance of sample= 0434
Absorbance of reagent blank= 0.043
Actual abosrbance of blank= 0.434-0.043= 0.391
Absorbance of sample + addition= 0.890
Abosrbnace of addition= 0.890-0.391=0.58
From Beer Lamberts law Absorbance= epsilon*L*C
whee epsilon is extinction coefficient, L is path length and C is the concentration
A1/C1=A2/C2 where A1 C1 refer to condition 1 and A2 C2 refer to condition 2
C2=A2*C1/A!= 0.58*1000/0.391=1488.3 ugml
when the abosrbnace was changed=
abosrbnace of sample =0.430-0.090=0.34
while that of sample = 0.890-0.34=0.55
concentration of unknwon =( 0.55/0.34)*1000=1617.6ug/ml
percentage error ={ (1617.6-1488.3)/1617*100}=7.993%
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