@article {403,
	title = {Evaluation of gas chromatographic isotope fractionation and process contamination by carbon in compound-specific radiocarbon analysis},
	journal = {Analytical Chemistry},
	volume = {79},
	year = {2007},
	note = {id: 615; 140ID Times Cited:11 Cited References Count:32},
	pages = {2042-2049},
	abstract = {The relevance of both modern and fossil carbon contamination as well as isotope fractionation during preparative gas chromatography for compound-specific radiocarbon analysis (CSRA) was evaluated. Two independent laboratories investigated the influence of modern carbon contamination in the sample cleanup procedure and preparative capillary gas chromatography (pcGC) of a radiocarbon-dead 3,3{\textquoteright},4,4{\textquoteright},5,5{\textquoteright}-hexachlorobiphenyl (PCB 169) reference. The isolated samples were analyzed for their C-14/C-12 ratio by accelerator mass spectrometry. Sample Delta C-14 values of -996 +/- 20 and -985 +/- 20\% agreed with a Delta C-14 of -995 +/- 20\% for the unprocessed PCB 169, suggesting that no significant contamination by nonfossil carbon was introduced during the sample preparation process at either laboratory. A reference compound containing a modern C-14/C-12 ratio (vanillin) was employed to evaluate process contamination from fossil C. No negative bias due to fossil C was observed (sample Delta C-14 value of 165 +/- 20\% agreed with Delta C-14 of 155 +/- 12\% for the unprocessed vanillin). The extent of isotopic fractionation that can be induced during pcGC was evaluated by partially collecting the vanillin model compound of modern C-14/C-12 abundance. A significant change in the delta C-13 and delta C-14 values was observed when only parts of the eluting peak were collected (delta C-13 values ranged from -15.75 to -49.91\% and delta C-14 values from -82.4 to +4.71\%). Delta C-14 values, which are normalized to a delta C-13 of -25\%, did not deviate significantly (-58.9 to -5.8\%, considering the uncertainty of similar to +/- 20\%). This means that normalization of radiocarbon results to a delta C-13 of -25\%, normally performed to remove effects of environmental isotope fractionation on C-14-based age determinations, also cor-rects sufficiently for putative isotopic fractionation that may occur during pcGC isolation of individual compounds for CSRA.},
	issn = {0003-2700},
	doi = {10.1021/Ac061821a},
	author = {Zencak, Z. and Reddy, C. M. and Teuten, E. L. and Xu, L. and McNichol, A. P. and Gustafsson, O.}
}
