Quantitative colorimetric determination of urinary p-aminophenol with an automated analyzer

We developed an automated colorimetric method for the quantitative determination of p-aminophenol with a Cobas Mira analyzer. The procedure can be used for the biological monitoring of human exposure to aniline. An absorbed aniline dose is extensively oxidized to p-aminophenol, which is excreted in urine mainly as glucurono- and sulfo- conjugates. After enzymatic hy-drolysis, we reacted the free compound with resorcinol in the presence of manganese ions to form an indophe-nol dye, which is measured at 550 nm. Excellent accuracy (102.8%, 103.9%, and 96.8 % at 2.5, 50, and 90 mg/L, respectively) and precision (7.7%, 2.1%, and 0.8 % CV for within-run and 11.1%, 4.7%, and 4.6 % for total reproduc-ibility at 2.5, 50, and 90 mg/L, respectively) were achieved over a linear concentration range of 2.0 to 10