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 δ 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‰ in δ 34 S (1 SD). The virtual absence of memory effects was established by analyzing adjacent samples exhibiting a large difference in δ 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 µg) 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 δ 34 S determination in small biological and mineral samples, minimizing matrix effects in various materials including sandstone, soil, and plant samples. Copyright © 2006 John Wiley & Sons, Ltd.