Sulfur Isotope Studies in Solid Organics: A Protocol for Utilizing Heterogeneous Standards and Secondary Ion Mass Spectrometry

We present sulfur isotope compositions (34S/32S) for nine solid organicssix petroleum cokes and three solid bitumensdemonstrating a reliable method using secondary ion mass spectrometry (SIMS) for complex, inhomogeneous materials. The protocol uses a homogeneous working standard, a heterogeneous matrix standard, and statistical measures to identify outliers in the analyses. We demonstrate screening methods that minimize the impact of heterogeneities on the SIMS data, leading to a calibrated matrix correction that can facilitate analysis of sulfur isotope composition in solid organics. The thiophenic sulfur and low H/C matrices of the selected materials are good surrogates for many solid organics. Furthermore, the approach is generally applicable to a wide range of materials and provides a means to obtain meaningful SIMS data when suitable homogeneous standards are unavailable.