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Reducing contamination parameters for clumped isotope analysis: The effect of lowering Porapak™ Q trap temperature to below –50°C
Author(s) -
Davies Amelia J.,
John Cédric M.
Publication year - 2017
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.7902
Subject(s) - isotopologue , chemistry , carbonate , analytical chemistry (journal) , contamination , analyte , isotope ratio mass spectrometry , mass spectrometry , isobaric process , fractionation , isotope , chromatography , molecule , organic chemistry , ecology , physics , quantum mechanics , biology , thermodynamics
Rationale Carbonate clumped isotope thermometry examines the thermodynamic preference of 13 C– 18 O bonds to form within the carbonate crystal lattice. The 13 C 18 O 16 O isotopologue in analyte CO 2 has a natural abundance of 44.4 ppm necessitating stringent purification procedures to remove contaminant molecules that may produce significant isobaric effects within range of the mass 47 isotopologue. Strict purifications of analyte CO 2 are thus required as well as reliable contamination indicators. Methods CO 2 purification was carried out by vacuum cryogenic purification through a static trap packed with Porapak™ Q (PPQ). The correlation between mass excesses on m/z 47, 48 and 49 in CO 2 produced by acid digestion of 12 natural samples was measured by isotope ratio mass spectrometry (IRMS). CO 2 from two contaminated carbonate samples was then purified at PPQ trap temperatures between –25 and –65°C and measured by IRMS to determine changes in mass excesses on m/z 47, 48 and 49. Finally carbonate standards, Carrara marble (CM) and ETH3, were purified at PPQ trap temperatures of –35 and –60°C to identify isotopic fractionation associated with lowering trap temperature. Results The correlation between mass excesses on m/z 47, 48 and 49 is determined to be sample dependent. Lowering the PPQ trap temperature to –60°C has a 78% success rate in decreasing Δ 48offset , a measure of sample contamination, to within an acceptable range (<1.5 ‰). Lowering the PPQ temperature in purification of CM and ETH3 is associated with decreases in the δ 13 C and δ 18 O values as a result of isotopic fractionation . We demonstrate that we can correct for fractionation at a trap temperature of –60°C. Conclusions Lowering the temperature of the Porapak Q trap to –60°C results in improved sample cleaning. It is possible to correct for fractionation in δ 13 C and δ 18 O values at lower PPQ trap temperatures using identically prepared standards. This result has important connotations for laboratories using similar sample preparation methods.