Coupled N, C and S stable isotope measurements using a dual‐column gas chromatography system

Many laboratories routinely analyze plant, animal and soil samples with elemental analyzers coupled to isotope ratio mass spectrometers, obtaining rapid results for nitrogen (%N, δ 15 N) and carbon (%C, δ 13 C) from the same sample. The coupled N and C measurements are possible because of a gas chromatography (GC) separation of N 2 and CO 2 gases produced in elemental analysis. Adding a second GC column allows additional measurement of sulfur (%S, δ 34 S) from the same sample, so that combined N, C and S information is obtained routinely. Samples are 1–15 mg, and replicates generally differ by less than 0.1‰ for δ 15 N, δ 13 C or δ 34 S. An example application shows that the N, C, and S measurement system allows a three‐dimensional view of element dynamics in estuarine systems that are undergoing pollution inputs from upstream watersheds. Extension of these GC principles should allow coupled H, C, N, and S isotope measurements in future work.