Abstract
Gas chromatography mass spectrometry (GC-MS) instruments provide researchers and clinicians with a vast amount of information on sample composition, thus these instruments are seen as gold standard in breath analysis research. However, there are many factors that can confound the data measured by GC-MS instruments. These factors will make interpretation of GC-MS data unreliable for breath analysis research. We present in this paper detailed studies of two of these factors: instrument variation over time and chemical degradation of known biomarkers during storage in sorbent tubes. We found that a single quadrupole MS showed larger variability in measurements than a quadrupole time-of-flight MS when the same mixture of chemical standards was analysed for a period of up to 8 weeks. We recommend procedures of normalising the data. Moreover, the stability studies of breath biomarkers like thioethers, previously found indicative of malaria, showed that there is a need to store the samples in sorbent tubes at low temperature, 6 °C, for no more than 20 days to avoid the total decay of the chemicals.
Highlights
The study and analysis of exhaled breath is an attractive and promising area of metabolomics and personalised medicine
(3) The day of analysis effect is irrespective of whether the tube was stored from Day 0 or spiked freshly on the day, both the fresh and stored samples have similar standard deviations in their measured values over the four weeks (Fig. 2). (4) There is considerable variation of measured values during the day, this can not be attributed to the degradation of the samples during the day as from Fig. 1a we can see the values do not always decrease over a day, and the standard deviation of the samples are not always larger in the afternoon
The large day of analysis effect in the Gas chromatography mass spectrometry (GC-MS) data means that some normalisation on the data will need to be performed when comparing samples that are measured over a long period of time
Summary
The study and analysis of exhaled breath is an attractive and promising area of metabolomics and personalised medicine. Breath carries a large number of volatile metabolites [1,2] and non-volatile compounds [3,4,5,6], potentially providing researchers with relevant biochemical information. Gas chromatography is seen as a gold standard in analysis of volatile compounds in breath research [8]. When coupled with mass spectrometry (GC-MS), these instruments provide researchers and clinicians with a vast amount of information about sample composition, which gives clues to the biochemical processes in the body. Breath samples can contain over a thousand compounds, and the fragmentation of the compounds by GC-MS instruments generates mass spectrometric fingerprints that can be searched using spectral libraries, such as that from the National Institute of Standards and Technology (NIST), to identify the detected compounds
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