High-performance liquid chromatography coupled with mass spectrometry applied to analyses of pesticides in water. Results obtained in HPLC/MS/APCI inpositive mode

Determinations of pesticides and their degradation products in natural wate rs, given the great heterogeneity of the sub stances involved, conventional ly demands the use of the following analytical methods: gas chromatography with different specific detectors such as the electron c apture detector. NPD thermo-ionic detector, and mass spectrometry. high-performance liquid chromatography combined with a diode array ultravio let detector of a spectrofluorimeter after derivatization, thin-layer chromatography (TLC) with detection of the isolated substances b y UV. With liquid chromatography, the most widely used detector is the diode-arra y UV detector. This method, recommended in French standard AFNOR T 90 123 ( EN ISO 11369) [1]1 represents a significant advance in the approach to thr identification of polar substances detected in unknown samples, compared wi th the results obtained by UV detection with a single wavelength However, t his method of detection does not guarantee the identification of the detect ed substances in absolute terms. Confirmation on a second column or by gas chromatography is therefore necessary. The atmospheric interfaces equipped with APCI (Atmospheric Pressure Chemica l Ionization) or ESI (Electrospray Ionization) ion sources help to broaden the field of application of the couplings of liquid chromatography with mas s spectrometry. and have seen substantial developments in recent years [2-4 ]. They offer performance in agreement with environmental requirements in t erms of quantification limits. sensitivity. simplicity of use and reliabili ty [5]. They are accordingly suitable for the identification and quantifica tion of pesticides and their conversion products in waters [6,7]. This article presents a summary of the results obtained on surface waters w ith the APCI interface in positive ionization mode, after extraction of the pesticides at neutral pH. The analyses were performed as part of a multi-r esidue approach applied to a priority list of 40 pesticides to be determine d in the surface waters of the Centre region of France. In addition to high-performance liquid chromatography combined with the dio de array UV detector and coupled with mass spectrometry, gas chromatography coupled with mass spectrometry was used as a technical complement, because of its suitability for apolar substances such as lindane, organochlorinate d pesticides, certain organophosphorus pesticides, trifluraline etc. For the other substances investigated, such as triazines and some of their degradation products, phenylureus, triazoles, amides and carbamates, high-p erformance liquid chromatography coupled in series with a UV detector and a mass spectrometer was employed. The results obtained with the diode array UV detector were compared with those obtained with the mass spectrometer in order to validate the results obtained with the latter detector. Acquisition and quantification methods optimized for HPLC/MS with APCI inte rface in positive ionization mode are presented in the article. Results on samples of surface waters with preconcentration following the li quid/liquid or liquid/solid methods are described. The analytical approach is set for: preconcentration methods, HPLC/MS acquisition parameters, quant ification methods, practical limits of quantification, and identification.