Determination of nickel in water samples by isotope dilution inductively coupled plasma mass spectrometry with sample introduction by carbonyl vapor generation

Nickel was determined in natural water samples by inductively coupled plasma mass spectrometry (ICP-MS) with sample introduction by on-line carbonyl vapor generation. The isotope dilution method was used for quantification with Ni-60 and Ni-62 as the major and minor isotopes. With sample introduction by the common pneumatic nebulization, the two isotopes may suffer from spectral interferences arising from molecular ions-such as CaO, ArMg and Na2O. In order to obtain accurate results free from spectral interferences, nickel in the water samples was reduced with sodium borohydride to its elemental form, and the mixed solution of sample and sodium borohydride subsequently met a stream of 10% CO gas to form the volatile nickel carbonyl. The generated carbonyl vapor was directed by a stream of argon carrier gas into the ICP after separation in a liquid-gas separator made of a polytetrafluoroethylene membrane tube. Optimum conditions for carbonyl generation were investigated. The analyte transport efficiency of the carbonyl generation method was estimated to be > 50%. Good agreement was achieved with the certified values in the analysis of two water reference materials, SLRS-3 riverine water and CASS-3 sea-water. The uncertainty of the analytical results was estimated to be 4.56% for CASS-3 and 1.64% for SLRS-3 with the coverage factor k = 2.