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Flushing time and storage effects on the accuracy and precision of carbon and oxygen isotope ratios of sample using the Gasbench II technique
Author(s) -
Paul Debajyoti,
Skrzypek Grzegorz
Publication year - 2006
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2559
Subject(s) - chemistry , isotope ratio mass spectrometry , analytical chemistry (journal) , gas composition , fractionation , mass spectrometry , isotope , environmental chemistry , carbon dioxide , radiochemistry , chromatography , physics , quantum mechanics , thermodynamics , organic chemistry
Continuous‐flow isotope ratio mass spectrometry interfaced with a Gasbench II is used for automated and faster analyses of δ 13 C and δ 18 O in water, carbonate, and air samples that are accurate and highly precise. Prior to online chemistry and measurement using the Gasbench technique, rubber septa‐capped glass vials are routinely flushed to remove air. Due to the small amounts of sample gas required for isotope analyses using current techniques, care should be taken to properly flush these vials to avoid contamination of sample gas with air. Our results indicate that isotopic composition of sample CO 2 gas remains constant when 10 mL vials are flushed (rate of 100 mL/min) for ≥600 s, whereas for vials flushed <600 s, the isotopic composition becomes substantially lighter with decreasing time of flushing, which affects the accuracy of analyses. This largely depends on the isotopic composition (and volume) of air that still remains after flushing. This effect is more pronounced on δ 18 O than on δ 13 C of sample CO 2 gas because there is very little carbon in the air. After 24 h storage in vials with punctured septa, both δ 13 C and δ 18 O of CO 2 become isotopically heavier compared with first day analyses, suggesting time‐dependent changes in isotopic composition. The magnitude of shift depends on the concentration and the isotopic composition of CO 2 in laboratory air as well as on fractionation due to outflow of sample gas or inflow of air via punctured septa. Contamination of sample gas with air can be observed as a secondary peak on chromatograms that precedes sample peaks, and the intensity of these peaks depends on the amount of air. Such peaks are always present with short flushing times. For accuracy and better precision, irrespective of the magnitude of the secondary peaks, the analyses should be discarded if these appear in the chromatograms. Copyright © 2006 John Wiley & Sons, Ltd.