standardized to a linear interpolation of frequent SF6 reference gas
peaks (Supplemental Fig. 1). In later analyses, we eliminated this
drift by isolating the sample gas heating system from the GC oven.
In this system, the Ar flow was preheated to a constant 320C outside
the GC oven before entering the upstream end of the transfer
line to the plasma torch. An additional heating tape was also added
at the ground glass connection between the transfer line and the
injector torch to improve the transfer of higher-boiling-point analytes
into the plasma. With these modifications, good peak shape
was obtained for compounds eluting at oven temperatures of up
to 300 C, permitting sulfur isotopic analysis of a wider range of
GC-amenable compounds. Because d34S values for SF6 drifted by
< 1‰ across the GC temperature program under these conditions,
drift correction was no longer necessary and standard peaks were
not required in the midst of the GC oven temperature program,
thus avoiding potential interference between standard and analyte
p