How long may a breath sample be stored for at  −80 °C? A study of the stability of volatile organic compounds trapped onto a mixed Tenax:Carbograph trap adsorbent bed from exhaled breath

Abstract

Thermal desorption is used extensively in exhaled breath volatile organic compound (VOC) analysis, and it is often necessary to store the adsorbent tube samples before analysis. The possible introduction of storage artefacts is an important potential confounding factor in the development of standard methodologies for breath sampling and analysis. The stability of VOCs trapped from breath samples onto a dual bed Tenax® TA:Carbograph adsorbent tube and stored −80°C was studied over 12.5 month. 25 samples were collected from a single male participant over 3 h and then stored at −80 °C. Randomly selected adsorbent tubes were subsequent analysed by thermal desorption-gas chromatography-mass spectrometry at 5 times points throughout the 12.5 month of the study. Toluene-d8, decane-d22 and hexadecane-d34 internal standards were used to manage the instrument variability throughout the duration of the study. A breath-matrix consisting of 161 endogenous and 423 exogenous VOC was created. Iterative orthogonal partial least squared discriminant analysis (OPLS-DA) and principal components analysis (PCA) indicated that it was not possible to detect storage artefacts at 1.5 month storage. By 6 month storage artefacts were discernible with significant changes observed for 27% of the recovered VOC. Endogenous VOC were observed to be more susceptible to storage. A paired two-tailed t-test on the endogenous compounds indicated that the maximum storage duration under these conditions was 1.5 month with 94% of the VOCs stable. This study indicates that a prudent approach is best adopted for the storage of adsorbent samples; storage times should be minimised, and storage time examined as a possible discriminatory factor in multivariate analysis.

Exhaled breath analysis: a review of ‘breath-taking’ methods for off-line analysis

“…Some factors that need to be considered include whether to use single or multi-bed sorbents which will depend on analytes of interest, and also the quantity of sorbent used. Whilst multi-bed sorbents can trap a larger range of different chemical species, both in terms of volatility but also polarity, analyte-sorbent interactions at the interfaces of the packed beds can affect reproducibility and thus compound recovery, and perhaps stability during storage (Kang and Paul Thomas 2016). …”

“…Concerns such as the stability of VOCs trapped onto sorbent materials, storage and also logistics are apparent. It has been shown that these tubes can be stored for up to 2 weeks prior to analysis (Harshman et al 2016; van der Schee et al 2013) whilst another study suggests longer (Kang and Paul Thomas 2016). Samples collected using this method can be analysed in the laboratory present in hospitals provided that the required analytical platform is available which would require a significant investment.…”

Effects of Sampling Conditions and Environmental Factors on Fecal Volatile Organic Compound Analysis by an Electronic Nose Device

“…Since VOCs either have a local, systemic or exogenous origin [14], these exhaled VOC studies are not restricted to pulmonary diseases, making exhaled volatiles an area of growing clinical interest. The latest efforts in this field have focused on detection of potential confounding factors and optimization of the sampling and storing techniques [15,16,17,18]. Despite these attempts, standardization remains a critical issue hampering implementation of breath analysis into clinical practice [19].…”

Exhaled breath analysis in the diagnosis of head and neck cancer

“…For samples collected onto a sorbent tube, a stable storage time of 1.5 months was achieved at −80°C. However, of almost 600 compounds that were studied, a significant amount showed discernible levels of change in concentration after 6 months of storage …”