A 5.00-mL sample of blood was treated with trichloroacetic acid to precipitate p

Question

A 5.00-mL sample of blood was treated with trichloroacetic acid to precipitate proteins. After centrifugation, the resulting solution was brought to pH 3 and extracted with two 5-mL portions of methyl isobutyl ketone containing the lead-complexing agent APCD. The extract was aspirated directly into an air/acetylene flame and yielded an absorbance of 0.523 at 283.3 nm. Five-milliliter aliquots of standard solutions containing 0.400 and 0.600 ppm of lead were treated in the same way and yielded absorbances of 0.396 and 0.599. Find the concentration of lead in the sample in ppm assuming that Beer's law is followed.

Explanation / Answer

5 ml of standard solution with Pb content,

0.600 ppm gave an absorbance = 0.599

0.400 ppm gave absorbance = 0.396

molar absorptivity = (0.599-0.396)/(0.6-0.4) = 1.015

beers law, absorbance = ebc

e = molar absorptivity

with absorbance for sample = 0.523

concentration of Pb in sample = 0.523/1.015 = 0.515 ppm in 5 ml of aliquot

[Or, Since the sample was size 5+ 5 ml,

concentration of Pb in the sample = 2 x 0.515 = 1.03 ppm]

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