Identification of alkyl dimethylbenzylammonium surfactants in water samples by solid-phase extraction followed by ion trap LC/MS and LC/MS/MS

A novel methodology was developed for the determination of alkyl (C-12, C-1 4, and C-16) dimethylbenzylammonium chloride (benzalkonium chloride Dr BAG, Chemical Abstract Service number: 8001-54-5) in water samples. This method is based on solid-phase extraction (SPE) using polymeric cartridges, follo wed by high-performance liquid chromatography/ion trap mass spectrometry (L C/MS) and tandem mass spectrometry (MS/MS) detection, equipped with an elec trospray interface in positive ion mode. Chromatographic separation was ach ieved for three BAC homologues by using a Cis column and a gradient of acet onitrile/10 millimolar aqueous ammonium formate. Total method recoveries we re higher than 71% in different water matrices. The main ions observed by L C/MS were at mass-to-charge ratios (m/z) of 304, 332, and 360, which corres pond to the molecular ions of the C-12, C-14, and C-16 alkyl BAG, respectiv ely. The unequivocal structural identification of these compounds in water samples was performed by LC/MS/MS after isolation and subsequent fragmentat ion of each molecular ion. The main fragmentation observed for the three di fferent homologues corresponded to the loss of the toluyl group in the chem ical structure, which leads to the fragment ions at m/z 212, 240, and 288 a nd a tropylium ion, characteristic of all homologues, at m/t 91. Detection limits for the methodology developed in this work were in the low nanogram- per-liter range. Concentration levels of BAG-ranging from 1.2 to 36.6 micro grams per liter-were found in surface-water samples collected downstream fr om different wastewater-treatment discharges, thus indicating its input and persistence through the wastewater-treatment process.