DETERMINATION OF ATRAZINE AND SIMAZINE IN ESTUARINE SAMPLES BY HIGH-RESOLUTION GAS-CHROMATOGRAPHY AND NITROGEN SELECTIVE DETECTION

A method for the determination of ultra trace concentrations of triazine herbicides in natural water using silica C18 solid-phase extraction (SPE) and high-resolution gas chromatography with nitrogen-selective detection (GC-NPD) has been developed and optimized for estuarine conditions. Recoveries of spiked dissolved simazine and atrazine at a concentration of 100 ng l-1 were 82-85% and 87-97%, respectively and were only slightly affected by the range of salinities and pH encountered for estuarine samples. The sediment-bound (particulate) triazines were ultrasonically extracted with high recoveries (86-91%) using dichloromethane. The water sample extracts were analysed without any additional clean up whereas the sediment extracts were purified using miniature silica gel columns. Nitrogen selective detection provided interference-free detection of simazine and atrazine in the extracts. The detection limits for simazine and atrazine in water and sediment were 1 ng l-1 for 1 l of water and 5 ng g-1 200 mg of suspended sediments. The reproducibility of the determination of atrazine and simazine in real water samples at low ng l-1 concentrations as shown by %R.S.D., was better than 10%. A comparison of the GC-NPD determination with an alternative method using ion selective detection (GC-ITD) showed very good agreement and indicated superior (ca. 5 fold) sensitivity of the NPD. The method was applied to a study of triazine herbicides in estuarine waters of the Rivers Tamar, Thames and Mersey.