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

Question

A 5.00mL sample of blood was treated with trichloroacetic acid to precipitate the proteins. After centrifugation, the resulting solution was brought to p^H 3.0 and extracted with two 5mL portions of methyl isobutyl ketone containing lead complexing agent APCD. The extract was aspirated directly into an air/acetylene flam and yielded an absorbance of 0.502 at 283.3nm. 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 0.369 and 0.599. Find the concentration of lead in the sample assuming that Beer's Law is followed.

Explanation / Answer

Answer:

For two points calibration we have:

Slope of the standard plot = (A2 – A1)/(C2 – C1)

Slope = (0.599 – 0.396)/(0.60 – 0.40) = 1.15

Therefore, can calculate the intercept from the straight line equation,

A = mC + b

0.599 = 1.15 × 0.40 + b

b = 0.139

Now, we can find the unknown concentration

0.502 = 1.15Cx + 0.139

Cx = 0.315 ppm

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