ISOTOPE-DILUTION GLOW-DISCHARGE MASS-SPECTROMETRY AS APPLIED TO THE ANALYSIS OF LEAD IN WASTE OIL SAMPLES

The application of isotope dilution (ID) to glow discharge mass spectrometry (GDMS) has been evaluated. Initial work with the analysis of solution residues has been modified to accommodate introduction of an isotopic spike. In evaluating ID-GDMS, elemental lead concentrations were determined in oil leachate samples. After equilibration of the sample and spike, a few hundred microliter volume of solution was mixed with a conducting host matrix. This slurry was then dried, homogenized and pressed into a GD cathode; after electrode formation, routine GDMS analysis (isotopic) was performed. Internal precision (within sample variation) was estimated to be better than 5% relative standard deviation (RSD) (1sigma) through the use of a computer model of the ID equation. External precision (between-sample variation) was better than 2% RSD (1sigma), a substantial improvement over most conventional GDMS analyses. For comparison purposes (i.e., where multiple isotopic spikes are impractical), a calibration curve was applied to the same data and gave external precision of better than 15% RSD. Both calibration curve and ID results compare well with those obtained by inductively coupled plasma atomic emission spectrometry.