Stable isotopes are
powerful tools for tracking biogenic carbon
in biofuel petroleum coprocessing. High-precision determination of
δ13C and δ15N values in bio-oils
and coprocessed biofuels by continuous-flow elemental analyzer coupled
to an isotope ratio mass spectrometer is challenging due to the physical
and chemical properties of the samples. Standard sample preparation
and measurement techniques such as syringe injection are susceptible
to fractionation due to evaporation of volatile compounds, incomplete
sample introduction due to sample viscosity, or contamination from
atmospheric nitrogen and carbon dioxide. In this work, a modified
cold-weld capsule sealer combined with an argon gas purge was used
to prepare a wide variety of bio-oil and coprocessed biofuel samples.
Measurements done in triplicate and quadruplicate and run on an EA-IRMS
showed no measurable atmospheric nitrogen contamination and resulted
in excellent reproducibility and precision of ±0.01‰ and
0.025‰, respectively, for δ13C. Additionally,
this method allows for even high-volatility samples to be stored for
long periods of time with no mass loss and analyzed, concurrently,
with commonly available solid isotope reference standards, eliminating
concerns of fractionation resulting from sample preparation, handling,
and introduction. The high precision of this measurement technique
makes it well suited for measurement of the often-small isotopic differences
seen in blended fuel products.