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 a pH of 3 and was extracted with two 5-mL portions of methyl isobutyl ketone containing the organic lead complexing agent APCD. The extract was aspirated directly into an air-acetylene flame yielding an absorbance of 0.502 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 absorbanees of 0.396 and 0.599. Find the concentration of lead in the sample assuming that Beer's law is followed.

Explanation / Answer

For two point calibration we have,

Slope of the standard plot is given as:

Slope = (A2 - A1)/(C2 - C1)

= (0.599 - 0.396)/(0.6 - 0.4)

= 0.203/0.2 = 1.015

Intercept can be calculated as follows:

A = mC + b ( y = mx + c type equation)

0.599 = (1.015 x 0.6) + b

b = - 0.01

So the unknown concentration is:

0.502 = 1.015 C - 0.01

C = 0.5044 (Answer)

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