On-line sample handling strategies for the trace-level determination of pesticides and their degradation products in environmental waters

An overview of the use of on-line techniques is presented. First, it includes the on-line coupling of solid-phase extraction and liquid chromatography, which is certainly the most commonly used automated technique really well adapted to the multiresidue analysis of pesticides in aqueous samples. The different parameters which govern the method (dimension of the pre-columns, type of sorbents, pre-columns in series, quantitative analysis) are discussed and applications to various waters are presented. Emphasis is given to the limits of detection obtained using UV diode array, fluorescence or electrochemical detection modes. The on-line post-column reaction detection coupled to liquid chromatography are also reviewed with emphasis on the determination of N-methylcarbamates. The performances of the on-line mass spectrometric detection coupled to solid-phase extraction and liquid chromatography are presented using thermospray, particle beam or electrospray. The main characteristics of the on-line coupling of solid-phase extraction and gas chromatography are also given, with various applications and corresponding detection limits. The recent results obtained with the on-line coupling of gas chromatography with solid-phase micro-extraction are outlined. Supercritical fluid extraction is also mentioned as a new sample handling technique which can be easily on-line coupled to the chromatographic separation.