SELECTIVE APPLICATION OF CHEMICAL SEPARATIONS TO ISOTOPE-DILUTION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRIC ANALYSES OF STANDARD REFERENCE MATERIALS

Isotope dilution has been used with ICP-MS to certify trace and ultrat race elements in both leaf and soil standard reference materials (SRMs ). Mass spectrometric interferences from the sample matrices prevented the direct determination of Cd, Ag, Mo, and Ni in these materials. Th e ICP-MS was used in a semiquantitative survey mode to identify interf erences and to develop customized separations. The fact that isotope d ilution analysis requires neither 100% recovery nor absolute isolation of the element(s) of interest results in considerable flexibility in the design of separations. Separated analytical samples were introduce d into the ICP-MS, and high accuracy quantitative results were based o n precise isotope ratio measurements made in the peak jump mode. Four transition metals, Cd, Ag, Mo, and Ni, in the nanogram to microgram pe r gram range were determined in five different SRMs with an average bi as uncertainty and imprecision of less than 1%.