The stability of selected herbicides preconcentrated from estuarine river waters on solid-phase extraction disks

The stability of atrazine, simazine, alachlor, metolachlor, and deethylatrazine on C-18 Empore disks has been determined. Estuarine water (100 mL) spiked at 3 mu g L(-1) with the target pesticide mixture was preconcentrated on the disks; the disks were then stored at -20 degrees C, 4 degrees C, and at room temperature for periods up to three months and were analyzed by gas chromatography with nitrogen-phosphorus detection. Complete recovery was observed after storage at -20 degrees C throughout the period of the study. Losses up to maximum of 10 % were observed after storage at 4 degrees C. Higher losses (up to 24 % for alachlor) occurred only at room temperature; the coefficient of variation for these determinations (8-11 %) was also higher than that for the others (3-5 %). The stability of the pesticides was dependent on the water matrix, on storage temperature, and on properties such as vapor pressure and water solubility.