Direct inductively coupled plasma mass spectrometric determination of cadmium in urine with special attention to matrix effect correction

Abstract

In the direct ICP-MS determination of Cd in urine, non-spectral matrix effects caused by high concentrations of sodium chloride can play an important role. In the present study, matrix effects were reduced by an optimum choice of the instrumental conditions and of the internal standard element, in this case Rh. Residual matrix effects were corrected with two procedures: the first was based on the signal of³⁵Cl and the second on the matrix effect experienced by the internal standard element. Average recovery with either procedure both of a Cd spike added to the samples and of the concentration found for a certified reference material was between 99 and 101% with a relative standard deviation of 2.3%. The correction factors in the correction equations were calculated from the recoveries of a limited number of recovery experiments. Sample preparation consisted of a 10-fold dilution of the sample with 1% HNO₃. ¹¹⁴Cd was found to be the best isotope with a detection limit of 8 ng l^–1 in a non-diluted urine sample. The Rh matrix effect-based procedure can most probably also be used to correct for matrix effects in other sample types.