Signal improvement in elemental analyzer/continuous flow isotope ratio mass spectrometry for samples with low sulfur contents using a pre-concentration technique for on-line concentration adjustment

Elemental analyzer/continuous flow isotope ratio mass spectrometry (EA/CF-IRMS) has become a standard procedure for the determination of delta(34)S values. Common procedures are, however, frequently less than satisfactory for organic as well as for mineral samples with very low concentrations of sulfur (<2000 ppm). Here we present a method which employs cold trapping of SO(2) to adjust the gas concentration for subsequent isotope signature determination. Analytical accuracy is comparable with common EA/CF-IRMS analysis without trapping, showing a precision of better than +/-0.4 per thousand in delta(34)S (1 SD). The virtual absence of memory effects was established by analyzing adjacent samples exhibiting a large difference in delta(34)S and by prolonged freezing of the carrier gas, yielding virtually no S concentration peak. The method was tested using less than 15% (6 microg) of the S required for a conventional isotope analysis at comparable signal intensity. Even smaller samples can be analyzed with high precision. This facilitates the on-line delta(34)S determination in small biological and mineral samples, minimizing matrix effects in various materials including sandstone, soil, and plant samples.