SAMPLE PREPARATION APPROACHES FOR ISOTOPE-DILUTION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRIC CERTIFICATION OF REFERENCE MATERIALS

Ratio measurements can be made by inductively coupled plasma mass spectrometry (ICP-MS) with precisions approaching 0.1-0.2% relative standard deviation, under carefully controlled conditions. This capability is well suited to isotope dilution quantification, since quantitative data are based solely on ratio measurements. Conversion of the precision of isotopic ratio measurements to accuracy requires attention to both the operation of the ICP mass spectrometer and to the sample preparation procedures. The concentration of Mg, Cd, Mo and Pb were determined in synthetic samples with average precision and accuracy of < 0.15%. Although more extensive chemistry was required, analytical precision was better than 0.15% for Cu and Cd in zinc ore and for Cu and Mo in domestic sludge.