Determination of sulfur as arsenic monosulfide ion by isotope dilution thermal ionization mass spectrometry

Abstract

A new procedure has been developed for the determination of microgram quantities of sulfur in metals by isotope dilution thermal ionization mass spectrometry. Typically 1-g metal samples are spiked with /sup 34/S-enriched spike and dissolved in a closed system to prevent loss of volatile S compounds using a mixture of HCl/HNO/sub 3/ acids which oxidized all S to sulfate. The S is reduced to H/sub 2/S and the sulfide precipitated as As/sub 2/S/sub 3/. The As/sub 2/S/sub 3/ is dissolved in an ammoniacal As/sup 3 +/ solution to yield an As/S atom ratio of two. A small portion of this solution, equivalent to 1.5 ..mu..g of S, is placed on a Re-flat filament with silica gel and the /sup 32/S//sup 34/S ratio is measured at 950/sup 0/C as the thermally produced /sup 75/As/sup 32/S/sup +/ and /sup 75/As/sup 34/S/sup +/ molecular ions. The ionization efficiency is about 0.1% and the precision of the /sup 32/S//sup 34/S ratio measurement is about 0.1% (1s). This procedure has been applied to the determination of S in 11 Cu base and Fe base alloys ranging in S concentration from 2.8 +/- 0.2 to 81 +/- 1 ..mu..g of S/g (ts, 95% confidence interval). Themore » chemical blank is the major source of uncertainty at these levels.« less