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 spec trometry (ICP-MS) with precisions approaching 0.1-0.2% relative standa rd deviation, under carefully controlled conditions. This capability i s well suited to isotope dilution quantification, since quantitative d ata are based solely on ratio measurements. Conversion of the precisio n of isotopic ratio measurements to accuracy requires attention to bot h the operation of the ICP mass spectrometer and to the sample prepara tion procedures. The concentration of Mg, Cd, Mo and Pb were determine d 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 d omestic sludge.