THE STABILITY OF SELECTED HERBICIDES PRECONCENTRATED FROM ESTUARINE RIVER WATERS ON SOLID-PHASE EXTRACTION DISKS

The stability of atrazine, simazine, alachlor, metolachlor, and deethy latrazine on C-18 Empore disks has been determined. Estuarine water (1 00 mL) spiked at 3 mu g L(-1) with the target pesticide mixture was pr econcentrated 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 dete ction. Complete recovery was observed after storage at -20 degrees C t hroughout the period of the study. Losses up to maximum of 10 % were o bserved after storage at 4 degrees C. Higher losses (up to 24 % for al achlor) occurred only at room temperature; the coefficient of variatio n for these determinations (8-11 %) was also higher than that for the others (3-5 %). The stability of the pesticides was dependent on the w ater matrix, on storage temperature, and on properties such as vapor p ressure and water solubility.