Nitrogen can substitute helium as a mobile phase in the analysis of wastewater treatment matrices for persistent organic pollutants by gas chromatography - electron capture detection system.

Municipal wastewater treatment plants are required to monitor persistent organic pollutants (POPs) in their wastewater treatment related discharges and to assess the impact of the discharges on the environment and public health. One tool for monitoring chlorinated organic pollutants particularly is a gas chromatographic (GC) system coupled to a pair of halogen-specific electron capture detectors (ECDs) with helium (He) as the mobile phase. He supplies, however, has become inconsistent and unreliable lately. In its place, N2 gas is evaluated in this study as a potential substitute for He in quantifying organochlorine pesticides, polychlorinated biphenyls, chlordane congeners and toxaphene in wastewater treatment related matrices (influent, effluent, benthic sediment, mussel tissue, and biosolids/sludge). N2 is inert, inexpensive and requires no additional hardware to incorporate into the basic functions of a GC-ECD. Our results show that, with the usual data quality controls (blank, laboratory control, matrix spike/duplicate and proficiency testing samples, and the fact that certified reference materials data met requirements), N2 can replace He for regulatory purposes. And when necessary, the N2-based retention times (tN) can be predicted reliably from He-based retention times (tHe), irrespective of column chemistry or POPs (here: tN = 1.90tHe + 0.04, R2 = 0.996).