Solid-phase extraction using C(18) bonded silica disks: interferences and analysis of chlorotriazines in seawater samples

The interferences in C(18) Empore extraction disks were obtained by processing 5 1. of HPLC water with average blanks of 1 ng/l. A C(19) alkane, plasticizers and the antioxidant Nonox A were identified in the blanks as possible interferences. The extraction of the components of the disks was carried out with methanol, acetonitrile and/or ethyl acetate with subsequent analysis by gas chromatography-mass spectrometry (GCMS). The identification of interferences was a requirement for the determination of the chlorotriazine herbicides atrazine and simazine, and of a transformation product, de-ethylatrazine, at concentration levels varying between 2 and 140 ng/l. Seawater samples of 3-28 parts-per-thousand were pre-filtered through a 47-mm diameter of 0.7 mum and subsequently with 0.45 mum glass-fibre filters to trap particulate matter, followed by Empore extraction disks of 500 mg C(18) bonded silica. Water volumes of 5 1. could be processed within 150 min. The disks were extracted with methanol, the extract was blown down under nitrogen, and the analytes were quantified by GC with nitrogen-phosphorus detection (NPD) with further confirmation using GCMS in the selected ion monitoring (SIM) mode. The proposed method has been applied to the determination of the environmental levels of atrazine and simazine in seawater samples of varying salinity. The recovery of de-ethylatrazine was 10%, so the method was not appropriate for this compound. The concentration of the herbicides has been plotted against the salinity values, showing a decrease in the levels as the salinity increases, with two inflexion points that indicate a non-conservative mixing with loss of the herbicides in the mixing zone of the estuary.