Determination of nickel in serum and urine by inductively coupled plasma mass spectrometry

Abstract

Methods are described for the measurement of Ni in human serum and urine by inductively coupled plasma mass spectrometry. In serum, interferences arising from Ca-, Na- and K-containing polyatomic species are corrected for by using principal components analysis with an internal Rh standard. The method is accurate to a level of 5 µg l^–1, as determined with the available reference materials, and a value an order of magnitude lower was achieved in pooled human serum. Within-run imprecision was 6%[relative standard deviation (RSD)] at the 1.5 µg l^–1 level and the pattern of interferences was stable across an analytical run of at least 15 samples. Nickel was measured directly on diluted urine following quantitative precipitation of Ca²⁺ with oxalic acid. The method is accurate to 40 µg l^–1 and has a within-run imprecision of 7%(RSD) at 4.5 µg l^–1 of Ni measured in human urine. Both ⁶¹Ni and ⁶²Ni are available for stable-isotope tracer studies, with ⁶¹Ni being preferred because only Cadependent polyatomic interferences are present at this m/z value and these can be overcome in urine by oxalate precipitation. Principal components analysis is also shown to distinguish between Ni sources enriched in both isotopes, simultaneously present with naturally abundant Ni, and therefore dual isotope tracer studies are feasible. The methods described are applicable at the concentration levels of Ni in body fluids that have been observed in human biokinetic studies.