The applicability of evacuated serological tubes for the collection of breath for isotopic analysis of CO2 by isotope ratio mass spectrometry

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Abstract
Stable isotope ratio mass spectrometry was used for the analysis of 13C and 18O in CO2 of human breath collected in evacuated serological tubes (Vacutainer® and Venoject®) and in gas sample bottles. There was a 1–2‰0 difference between the δ13CPDB values obtained from breath CO2 collected in gas bottles and that collected in two batches of Vacutainer. δ18OPDB differed between Vacutainers and gas bottles by as much as 14%0 and standard deviations within the two batches of Vacutainer were 0.7 and 1.8%0. The poor reproducibility and accuracy for the δ18OPDB values was caused by the presence of a contaminant which originated from the rubber septa of the Vacutainers. The results show that it is not possible to obtain δ18OPDB values with a high degree of accuracy or precision for breath samples collected in Vacutainers. However, with selection of less contaminated or re‐evacuated batches, δ13CPDB analysis of breath CO2 in Vacutainers may provide acceptable accuracy and precision. δ13CPDB and δ18OPDB values measured in breath collected in non‐sterile Venoject tubes were also significantly different from those obtained with gas bottles. However, the accuracy and precision of these determinations were considerably better than in sterilized Vacutainer tubes. As a result of these comparisons it is concluded that gas bottles are necessary for the full accuracy and precision of stable isotope ratio analysis mass spectrometers to be exploited in breath CO2 analysis. However, automated analysis of breath CO2 collected in non‐sterile Venoject tubes will provide an accuracy and precision that is suitable for most biological studies.