Examination of Intermolecular Forces Influencing Headspace Analysis of Biological Samples

Headspace analysis is an effective method for assessing the concentrations of volatile and semi-volatile metabolites in biological samples. In particular, solid-phase microextraction (SPME) is an efficient tool for headspace analyses. Metabolites present in the sample are the typical targets of headspace analysis (rather than the vapor phase concentration) for making measurements on sample donors (e.g., biomarkers of health or disease). Accordingly, intermolecular forces between metabolites and matrix may prevent a complete profile of the metabolite composition in the biosamples from being revealed. To assess sources of such interactions, several volatile compounds in various sample mediums were examined. Small volatile metabolites typical of human biosamples were the volatile compounds selected for this study. Test media included lipid or serum solution to simulate biological samples commonly encouraged in biomarker discovery. Headspace concentrations of volatile analytes were compared using solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). Observed levels of metabolites in headspace varied among the different media, despite being fortified at equal concentrations in the samples. Overall, lower headspace responses were observed in samples containing proteins or lipids. It was found that these strong intermolecular interactions arose from irreversible chemical bonds between the volatile molecules and component of the sample matrix. However, headspace responses could be maximized when the analysis was performed at temperatures ranging from 60 to 70 °C. Furthermore, normalization of peak responses to an internal standard did not always account for these interactions.