Method for the selective detection of petroleum hydrocarbon in an environmental sample containing natural organic matter. The method includes subjecting the sample to infrared (IR) radiation, and detecting an IR signal centered on a signal at 1380 cm−1, 2690 cm−1, 2730 cm−1, 2830 cm−1, 2870 cm−1, 4164 cm−1, 4256 cm−1, 4329 cm−1 and/or 4388 cm−1. Detection of the IR signal indicates the presence of petroleum hydrocarbon in said sample.