Abstract
Advances in sulfur isotope measurement techniques have led to increased
analytical precision. However, accurate measurement of
36S remains a challenge, hindering research such as
that focused on microbial metabolic processes. This difficulty arises
partly from isobaric interferences of 36SF
5 + at m/z = 131 amu, namely
186WF 4 2+ and
12C 3F 5
+ which lead to scale compression. Our study develops
an interference-free four-sulfur isotope measurement method using the
high-resolution mass spectrometer Panorama. Panorama’s peak scan showed
that the relative intensity of 186WF 4
2+ was initially 9.4% of 36SF
5 + but was reduced to 1.5% through
tuning, while the 12C 3F
5 + relative intensity dropped from
74% to 40% after flushing with air and continued to decrease over
time. Theoretically, an unresolved isobaric interference with 2%
relative intensity could cause a 1‰ underestimation in a sample with a
real δ 36S value of +60‰. We analyzed three IAEA
sulfur isotope standards. Recommended 36S values we
obtained relative to IAEA-S-1 are Δ 36S
IAEA-S-2 = 1.238 ± 0.040‰, and Δ 36S
IAEA-S-3 = -0.882 ± 0.030‰. For cases where the
interferences cannot be removed, we offer a calibration method to
correct for the scale compression effect. This involves bracketing two
or more IAEA standards in the sample measurement sequence and then
extending the measured IAEA δ 36S values by a
calibration factor to match the values reported in this study. Applying
this calibration factor to the samples effectively corrects the scale
compression effect.