Extending PTR based breath analysis to real-time monitoring of reactive volatile organic compounds

• Published in: Analyst (London) Vol. 144; no. 24; pp. 7359 - 7367
• Main Authors: Pugliese, Giovanni, Trefz, Phillip, Brock, Beate, Schubert, Jochen K, Miekisch, Wolfram
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 02.12.2019
• Subjects: Acetone; Adult; Aliphatic amines; Breath Tests - methods; Calibration; Design optimization; Diet, High-Protein; Diet, Protein-Restricted; Drift tubes; Electric fields; Female; Humans; In vivo methods and tests; Limit of Detection; Linearity; Male; Mass spectrometry; Mass Spectrometry - methods; Mathematical analysis; Middle Aged; Monitoring; Nitrogen; Proof of Concept Study; Protein metabolism; Proteins; Reaction time; Trimethylamine; VOCs; Volatile organic compounds; Volatile Organic Compounds - analysis; Young Adult
• ISSN: 0003-2654; 1364-5528; 1364-5528
• DOI: 10.1039/c9an01478k

Reactive exhaled volatile organic compounds (VOCs) such as nitrogen- and sulfur-containing substances may be related to diseases, metabolic processes and bacterial activity. As these compounds may interact with any surface of the analytical system, time-resolved monitoring and reliable quantification is difficult. We describe a proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) based analytical method for direct breath-resolved monitoring of reactive compounds. Aliphatic amines were used as test substances. Matrix adapted gas standards were generated by means of a liquid calibration unit. Calibration conditions were adapted in terms of materials, temperature and equilibration time. PTR-ToF-MS conditions were optimized in terms of inlet materials, transfer line and drift tube temperature and drift tube reduced electric field ( E / N ). Optimized PTR conditions in combination with inert materials and high temperatures considerably reduced the interactions of compounds with the surfaces of the analytical system. Good linearity ( R 2 > 0.99, RSDs < 5%) with LODs between 0.15 ppbV and 1.23 ppbV and LOQs between 0.24 ppbV and 1.94 ppbV could be achieved. The method was then applied to breath-resolved monitoring of reactive compounds in 17 healthy subjects after high and low oral protein challenge. Exhaled concentrations of trimethylamine, indole, methanethiol, dimethylsulfide, acetone, 2-propanol, 2-butanone and phenol showed significant changes after protein intake. Methanethiol concentrations increased 6-fold within minutes after the protein intake. Optimization of methods and instrument design enabled reliable breath-resolved PTR-MS based analysis of exhaled reactive VOCs in the sub-ppbV range. Continuous in vivo monitoring of exhaled amines and sulphur containing compounds may provide novel non-invasive insight into endogenous and gut bacteria driven protein metabolism. Direct time resolved mass spectrometric monitoring of reactive exhaled nitrogen- and sulfur-containing volatile organic compounds (VOCs) related to metabolic processes, diseases and bacterial activity.