Grass material as a modern process standard for 14 C analysis of n - alkanes

One of the difficulties in reporting accurate radiocarbon results from compoundspecific radiocarbon analysis (CSRA) is the lack of suitable process standard materials to correct for the amount and C content of carbon added during extensive sample processing. We evaluated the use of n-alkanes extracted from modern grass material (1.224 ±0.006 fraction modern) as process standards for CSRA. The n-alkanes were isolated using preparative capillary gas chromatography (PCGC) from two independent chemical extraction methods applied to the grass. Since this was our first assessment of the C content of the grass n-alkanes, we corrected for extraneous carbon derived from PCGC isolation using commercially available single compounds of modern and C-free content. Results were consistent across the two extraction methods showing that the C29 n-alkane has a fraction modern value that is within 1σ of the bulk value of the grass while C31 n-alkane and less abundant nalkanes have values within 2σ of the bulk value of the grass. C29 and C31 n-alkanes were the most abundant n-alkanes in the grass and, as such, the more feasible for collection of sufficient amounts of carbon for accelerator mass spectrometry (AMS) analysis. Our results suggest that choosing a grass n-alkane with an elution time closest to that of the unknowns may be advisable due to possibly greater effect from GC column bleed (C-free) at later elution times. We conclude that C29 and C31 nalkanes in modern grass of known C content can be used as in-house standards to correct for the addition of C-free carbon during sample preparation for C analysis of n-alkanes.