Measurement of Sulfur Isotope Compositions by Tunable Laser Spectroscopy of SO₂

Sulfur isotope measurements offer comprehensive information on the origin and history of natural materials. Tunable laser spectroscopy is a powerful analytical technique for isotope analysis that has proven itself readily adaptable for in situ terrestrial and planetary measurements. Measurements of δ³⁴S in SO₂ were made using tunable laser spectroscopy of combusted gas samples from six sulfur-bearing solids with δ³⁴S ranging from −34 to +22‰ (also measured with mass spectrometry). Standard deviation between laser and mass spectrometer measurements was 3.7‰ for sample sizes of 200 ± 75 nmol SO₂. Although SO₂(g) decreased 9% over 15 min upon entrainment in the analysis cell from wall uptake, observed fractionation was insignificant (+0.2 ± 0.6‰). We also describe a strong, distinct ³³SO₂ rovibrational transition in the same spectral region, which may enable simultaneous δ³⁴S and Δ³³S measurements.