The effects of Porapak(TM) trap temperature on delta super(18)O, delta super(13)C, and Delta sub(47) values in preparing samples for clumped isotope analysis

• Published in: Rapid communications in mass spectrometry Vol. 30; no. 1; pp. 199 - 208
• Main Authors: Petersen, Sierra V, Winkelstern, Ian Z, Lohmann, Kyger C, Meyer, Kyle W
• Format: Journal Article
• Language: English
• Published: 01-01-2016
• Subjects: Carbon dioxide; Carbonates; Contaminants; Isotopes; Mass spectrometry; Retrieval
• ISSN: 0951-4198; 1097-0231
• DOI: 10.1002/rcm.7438

Rationale The clumped isotope paleothermometer, a new proxy widely applicable in studies of paleoclimate, tectonics, and paleontology, relates the abundance of doubly substituted isotopologues of carbonate-derived CO sub(2) to the temperature of formation of the carbonate phase. As this technique becomes more widely used, more is discovered about the effects of everyday laboratory procedures on the clumped isotopic composition of CO sub(2) gas. Methods Preparation of CO sub(2) for clumped isotope analysis requires the removal of isobaric contaminants prior to measurement, achieved dynamically by passing the CO sub(2) through a gas chromatography column using a helium carrier gas or cryogenically pumping CO sub(2) through a static trap filled with Porapak(TM) Q (PPQ) material. The stable and clumped isotopic compositions of carbonate standards prepared at PPQ trap temperatures between -40 degree C and -10 degree C were measured by isotope ratio mass spectrometry to evaluate potential artifacts introduced by the static PPQ trap method. Results The stable isotopic composition of carbonates run at temperatures below -20 degree C was fractionated, despite achieving >99% retrieval of gas at temperatures as cold as -30 degree C. The delta super(13)C and delta super(18)O values decreased by ~0.01 and ~0.03 ppt/( degree C below -20 degree C). The raw Delta sub(47) values decreased by 0.003-0.005 ppt/( degree C below -20 degree C), but the final reference-frame-corrected values ( Delta sub(47-RFAC)) were unaffected as long as the carbonate samples and standard gases were prepared identically. Conclusions Preparing carbonate samples for clumped isotope analysis using a PPQ trap that is too cold can result in erroneous stable isotopic compositions. New and existing labs using the static PPQ trap cleaning procedure should determine the ideal PPQ trap temperature for their particular system through monitoring not only yield through the PPQ trap, but also stable isotopic composition at various PPQ trap temperatures.