Abstract

Sector field ICP-MS, commonly referred to as high resolution ICP-MS, is a powerful technique that is very suited to determining elements at ultra-trace levels and/or elements which are spectrally interfered at low mass resolution, without any preliminary work such as preconcentration or analyte/matrix separation. The interest for the accurate and precise determination of (ultra-) trace elements in water, e.g., drinking and ground water, derives from the necessity to ensure the quality of drinking water supplies and to protect natural water reserves. This paper describes the suitability of sector field ICP-MS for water analysis owing to the low detection limits, even for elements spectrally interfered at low mass resolution, and the nearly negligible matrix effects. This has been demonstrated by the measurement of the levels of several ultra-(trace) elements (Ag, Cd, V, Cr, As and Se) in a number of mineral waters originating from Belgium and France. Although none of the concentrations determined exceeded the drinking water guidelines, a few surprisingly high V and As values were encountered for a particular mineral water source. Evidently, accuracy is a prerequisite for analytical data to be relevant. Therefore an international certification campaign was organised by the European Union (Standards, Measurement and Testing, SMT Programme) for the determination of Al, Mg, Ca, Mn and Fe in groundwater candidate reference materials. Matrix effects were not negligible and necessitated dilution of the samples. With single standard addition for calibration, combined with the use of appropriate internal standards, accurate results in good agreement with the results obtained by other techniques in other laboratories were obtained with sector field ICP-MS. An intercomparison study was also performed in co-operation with a sub-division (RIZA) of the Dutch Ministry of Transport, Public Works and Water Management, in which the concentrations of some heavy metals were determined in pore water samples. The actual purpose was the investigation of heavy metal fluxes from the water-floor towards the surface water. The elements of interest, Cr, Ni, Cu, Zn, Cd and Pb (mostly present at sub-ppb levels), were determined using sector field-ICP-MS since this technique offered the lowest detection limits attainable.