Atomic absorption spectrometry was used with the method of standard additions to

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 = 0.047

Absorbance of sample = 0.392

Absorbance of sample plus addition = 0.732

A) What was the concentration of the cadmium in the waste stream sample?

B) Later, the analyst learned that the blank was not truly a reagent blank, but water. The absorbance of the actual reagent blank, was 0.11. Calculate the cadmium concentration using the new information of the blank.

C) Calculate the percent error caused by using water instead of the reagent blank.

Explanation / Answer

A)
0.392-0.047=0.345 absorbance of the sample
0.732-0.345=0.387 absorbance of the standard addition
0.01g/1000 L=1*10^-5 g/L of standard addition of cadmium
Current transition residual cadmium concentration=(1*10^-5 g/L*0.345)/0.387=8.915*10^-6g/L

B)
0.392-0.11=0.282 absorbance of the sample
0.732-0.282=0.45 absorbance of the standard addition
0.01g/1000 L=1*10^-5 g/L of standard addition of cadmium
Current transition residual cadmium concentration=(1*10^-5 g/L*0.282)/0.45=6.27*10^-6g/L

C)
w%=((8.915*10^-6g/L- 6.27*10^-6g/L)/8.915*10^-6g/L)*100=29.7%

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