Colorimetric assay of 2,2-bis(4-chlorophenyl)acetic acid (DDA) in urine

2,2-Bis(4-chlorophenyl) acetic acid (DDA) was extracted from acidified urine at pH 2 by benzene. It was complexed by partitioning with crystal violet in acetic acid to yield a blue color which was quantitated at 610 nm. Its identity was confirmed by paper chromatographic separation. The DDA excretion in nine subjects ranged from 0.024 to 0.130 μg/ml with a mean of 0.065 while that determined by gas chromatography ranged from 0.038 to 0.120 with a mean of 0.069.