AbstractA method was developed to concentrate fractions high in bacterial mutagenicity from diesel exhaust particle (DEP) extracts. The two‐step fractionation of organic extracts of DEP employed Sephadex LH‐20 followed by thin‐layer chromatography (TLC). In both steps, nitro‐substituted polycyclic aromatic hydrocarbons (nitro‐PAHs) were found to co‐elute with the fractions of highest specific bacterial mutagenic activity. Although recoveries of mass and mutagenicity from the LH‐20 fractionation were high, very low (20–30) recovery of mutagenicity was found after TLC. Recovery studies using14C‐labeled 1‐nitropyrene showed that 78 of the compound was recovered unaltered through the combined fractionation. The most bioactive TLC subfraction was chromatographed using gas chromatography with thermionic specific detection. A sizeable peak was found to co‐elute with a nitropyrene standard, but no peak was found co‐eluting with nitrofluoranthene. Triple quadrapole mass spectrometry was used to measure the concentrations of nitropyrene in each of the fractions. Nitropyrene was enriched 160‐fold in the most bioactive TLC subfraction over the starting material, for a final concentration of over 3200 μg g−1. Masses corresponding to several two‐ and three‐ring methylated nitro‐PAHs were found in the same fraction, including nitro‐(methylbiphenyls/methylacenapthenes) and nitro‐(
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