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.