Determination of organonitrogen pesticides in large volumes of surface water by liquid-liquid and solid-phase extraction using gas chromatography with nitrogen-phosphorus detection and liquid chromatography with atmospheric pressure chemical ionization mass spectrometry.

During a recent study to determine the fluxes and fates of contaminants in the St. Lawrence River, the majority of organonitrogen pesticides analysed in samples of surface water were found in the dissolved phase. This paper compares two extraction techniques and two analytical techniques for 10 chemicals (metolachlor, seven triazines and two degradation products of atrazine-cyanazine-propazine and simazine) in the dissolved phase in large volumes of surface water, using a fibre glass filter with 0.7 micron porosity. Samples of filtered surface water (1-20 l) were extracted by means of a liquid-liquid technique using the Goulden large-sample extractor, and by means of a solid-phase extraction technique, using cartridges filled with 500 mg of a large particle-size graphitized carbon black as adsorbent: Carbopack B (500-666 microns). The pesticides were analysed by gas chromatography on two DB-5 and DB-210 capillary columns with nitrogen-phosphorus detection (GC-NPD) and by liquid chromatography coupled with mass spectrometry equipped with an atmospheric pressure chemical ionization interface (LC-APCI-MS). The recoveries were high (67-100%) for the majority of the target pesticides in a volume of 17.85 l of Milli-Q water, compared to recoveries in the same volume of filtered surface water (51-102%). The detection limits ranged from 0.4 to 4 ng/l and from 0.6 to 3 ng/l for GC-NPD and LC-ACPI-MS techniques, respectively.