GLOW-DISCHARGE MASS-SPECTROMETRIC ANALYSIS OF TRACE-METALS IN PETROLEUM

A previously reported method of analyzing solution residues by glow discharge mass spectrometry (GDMS) has been extended to the analysis of petroleum. Results showed that cathode formation could not be achieved simply by drying and pressing with a conductive host matrix (as in the case of the aqueous solutions), and an additional low-temperature ashing step was incorporated to reduce the organic material to a dried residue. The residue was pressed with a conducting host into a pin, which was subjected to conventional GDMS analysis. The results from two NIST aqueous reference solutions were compared to those from two SPEX standard reference oils; only small differences in relative ion yields (less than 10% average) were observed between the two types of sample. This is well within experimental error. By applying relative sensitivity factors, good accuracy was obtained (better than 5% average error); this indicates minimal matrix effects. Good agreement was also observed between results obtained by using the GDMS methodology and those obtained using EPA-approved inductively coupled plasma optical emission spectroscopy calibration curve procedures. One limitation noted in the GDMS analysis was the increased number and type of polyatomic interferences, presumably caused by the residual organic constituents of the oil.