Direct isotope ratio measurement of ultra-trace lead in waters by double focusing inductively coupled plasma mass spectrometry with an ultrasonic nebuliser and a desolvation unit

A double focusing inductively coupled plasma mass spectrometer coupled with an ultrasonic nebuliser and a desolvation unit was used to measure Pb-206/ Pb-207, Pb-206/Pb-208 and Pb-207/Pb-208 isotope ratios in Pb standard SRM98 1, diluted to total Pb concentrations ranging from 1 to 1000 ng l(-1). The synthetic water standard SRM1654d, diluted by a factor of 100, and the natu ral riverine water standard SLRS-3 were also analysed for their Pb isotope ratios. It was found that lead isotope data with good accuracy could be obt ained down to 10 ng l(-1). At 1 ng l(-1), the blanks became too problematic . The internal precisions found appear to be well correlated with counting statistics, and range from ca. 3 to 0.2% RSD, depending on the Pb concentra tion and the instrument sensitivity. The long term reproducibility is even better and may reach values down to 0.02% RSD at concentrations above 100 n g l(-1) total Pb. Lead isotope values are proposed for the SRM1654d and SLR S-3 water standards. It appears that the reproducibility is affected by mat rix effects in the latter, natural water. In future work aimed at lead isot ope measurements at the sub-ng l(-1) level with this approach, it will be n ecessary to solve serious instrument contamination and memory effects for P b.