Determination of the herbicide amitrole in water with pre-column derivatization, liquid chromatography and tandem mass spectrometry

Amitrole is a widely used polar herbicide, difficult to isolate from water. Due to its persistence, it can easily pollute ground and surface waters used in drinking water production. A fully automated on-line SPE–HPLC (solid-phase extraction–high-performance liquid chromatography) method with atmospheric pressure chemical ionisation–tandem mass spectrometry detection is described for the determination of amitrole. A pre-column derivatization with 9-fluorenylmethoxycarbonyl chloride directly in the native aqueous sample allows an enrichment step by SPE and HPLC separation. Due to the sensitivity of tandem mass spectrometric detection, a limit of detection and quantification as low as 0.025 μg/l was achieved in drinking water and ground and surface water. Based on the constant ratio of two selected product ions together with the retention time, the identification is very selective and quantitation is very reliable. The performance characteristics of the described method fully meet the requirements set by the EU Drinking Water Directive: recoveries of >95% in drinking water and >75% in surface water were achieved, as well as RSD values for repeatability of <9% in drinking water and <12% in surface water (determined at a spiking level of 0.1 μg/l). The method was successfully applied to real samples of ground and surface water with actual concentration up to 1.1 μg/l.