Atomic absorption spectrometry was used with the method of standard additions to
ID: 976467 • 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 mu of a 1000.0 mug/mL Cd standard was added to 10.0 mL of solution. The following data were obtained: Absorbance of reagent blank = 0.024 Absorbance of sample = 0.385 Absorbance of sample plus addition = 0.799 What was the concentration of the cadmium in the waste stream sample? Oter, the analyst learned that the blank was not truly a reagent blank, but water. The absorbance of the actual reagent blank, was 0.058. 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
10 ul of 1000 ug/ml Cd standard has = 10 ug Cd
absorbance of standard = 0.799 - 0.385 - 0.024 = 0.390
10 ug in 10 ml = 1 ug/1ml Cd std gave absorbance = 0.390
absorbance of sample = 0.385 - 0.024 = 0.361
sample has = 0.361 x 10/0.390 = 9.256 ug in 10 ml = 0.925 ug/ml Cd in it
If reagent blank now has absorbance = 0.058
absorbance of standard = 0.799 - 0.385 - 0.058 = 0.356
10 ug in 10 ml = 1 ug/1ml Cd std gave absorbance = 0.356
absorbance of sample = 0.385 - 0.058 = 0.327
sample has = 0.327 x 10/0.356 = 9.185 ug in 10 ml = 0.918 ug/ml Cd in it
Percentage error = (0.925 - 0.918/0.918) x 100 = 0.76%
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