137. Solving a chemistry problem

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To determine the lead content, a 5.00 ml blood sample was treated with tichloroacetic acid for protein coagulation and centrifuged. The resulting solution was adjusted to a pH of 3, a solution of ammonium pyrrolidinedithiocarbaminate was added, and the resulting intracomplex lead compound was extracted with two portions of 5.00 ml of methyl isobutyl ketone. The extracts were combined, sprayed in an acetyl-air flame. Optical density measured at 283.3 nm was 0.502. For two aliquots of 5.00 ml of standard solutions containing 0.40 and 0.60 μg of lead and treated in a similar way, the optical densities were 0.396 and 0.599. Calculate the amount of lead (μg) in the blood sample.