High-throughput method for simultaneous quantification of N, C and S stable isotopes and contents in organics and soils.

Rationale Information about the sulfur stable isotope composition (δ34S value) of organic materials and sediments, in addition to their nitrogen (δ15N value) and carbon (δ13C value) stable isotope compositions, can provide insights into mechanisms and processes in different areas of biological and geological research. The quantification of δ34S values has traditionally required an additional and often more difficult analytical procedure than NC dual analysis. Here, we report on the development of a high-throughput method that simultaneously measures the elemental and isotopic compositions of N, C and S in a single sample, and over a wide range of sample sizes and C/N and C/S ratios. Methods We tested a commercially available CHNOS elemental analyzer in line with an isotope ratio mass spectrometer for the simultaneous quantification of N, C and S stable isotope ratios and contents, and modified the elemental analyzer in order to overcome the interference of 18O in δ34S values, to minimize any water condensation that could also influence S memory, and to achieve the complete reduction of nitrogen oxides to N2 gas for accurate measurement of δ15N values. A selection of organic materials and soils was analyzed with a ratio of 1:1.4 standards to unknowns per run. Results The modifications allowed high quality measurements for N, C and S isotope ratios simultaneously (1 SD of ±0.13‰ for δ15N value, ±0.12‰ for δ13C value, and ±0.4‰ for δ34S value), with high throughput (>75 unknowns per run) and over a wide range of element amount per capsule (25 to 500 μg N, 200–4000 μg C, and 8–120 μg S). Conclusions This method is suitable for widespread use and can significantly enhance the application of δ34S measurements in a broad range of soils and organic samples in ecological and biogeochemical research. Copyright © 2016 John Wiley & Sons, Ltd.