Max Wilkinson - Effects of humidity, dry purging and sorbent choice on VOC recovery during breath sampling
Max Wilkinson has recently been awarded a PhD at the University of Manchester under the supervision of Steve Fowler and will be continuing to work with the group for the next two years. His research has been focussed on the optimisation of breath sampling to improve the reproducibility of results. Max is currently working on the analysis of GC-MS data from clinical studies investigating asthma and COPD.
Offline breath analysis by GC-MS requires the use of sorbent traps to concentrate and store volatile compounds. The selection of which sorbent to use and best practices for managing water retention are important considerations to allow for reproducible, untargeted, biomarker discovery in water saturated breath samples.
To assess three commonly used sorbent materials for their use in breath volatile sampling and determine how the high relative humidity inherent in such samples effects the capture of volatile compounds of interest.
One single bed sorbent (TenaxGR) and two dual bed sorbents (TenaxTA / Carbograph1TD and TenaxTA / Carbograph5TD) were selected as they are the most commonly used sorbents in the breath sampling literature. Water retention and dry purge rates were determined. The recovery of 29 compounds in a standard mix loaded using high humidity gas was tested for each sorbent and compared to loading in dry gas. Finally, breath samples were sampled simultaneously on to each sorbent type using the ReCIVA, a proprietary breath sampler, and analysed by TD-GC-MS.
All three sorbents exhibited acceptable reproducibility when loaded with the standard mix in dry gas. Loading the standard mix in humid gas led to reduced recovery of compounds based on their chemical properties. Dry purging performance for each sorbent material was assessed and was shown to be 1.14, 1.13 and 0.89 mg H2O min-1 for TenaxGR, TenaxTA/Carbograph1TD and TenaxTA/Carbograph5TD respectively. A comparison of breath profiles on different sorbents showed differences in background artefacts (sulfur dioxide, cyclopenten-1-one and 3-nonene) and endogenous breath compounds (2-methyl-furan and furfural).
All three sorbents performed equally well when the standard mix was loaded onto them. High relative humidity during sampling reduces the ability of sorbent tubes to capture volatile compounds. This effect is dependent on the chemical properties of the compound and could impact method detection limits during breath sampling studies. Sufficient water to impair accurate analysis was retained on all tube and dry purging times are suggested. Minimal differences were observed between sorbent materials when used to sample breath, however, suggestions are provided for sorbent selection for future studies.