Setting Up And Characterization Of A Direct Mass Spectrometry-based Device For The Analysis Of Exhaled Volatile Organic Compounds In Human Breath

Secondary electrospray ionization(SESI)is a novel universal soft ionization technique and promising for qualitative analysis of exhaled volatile organic compounds(VOCs)while coupled with mass spectrometry.Recent studies have suggested that SESI with high resolution mass spectrometry(HRMS,R>10000)can further advance the accurate identification of elemental composition,which is critical for the translational application of SESI-MS to disease diagnosis,environmental exposure,etc.However,there is no commercial SESI source yet and thus the results obtained from different labs are less comparable;moreover,the influence of high resolution and mass accuracy on the qualitative analysis of exhaled VOCs has also been not well understood.Therefore,this study has been aimed at developing a high performance secondary nanoESI ion source(Sec-nanoESI),which was coupled with HRMS and,tentatively applying for the qualitative analysis of exhaled VOCs in the breath from normal subjects.The most important results are presented as follows:(1)A setup based on Sec-nanoESI-HRMS has been successfully developed by using a high performance commercial nanoESI ion source together with a commercial Q Exactive hybrid quadrupole orbitrap high resolution mass spectrometer(R=120000).(2)Isobaric ions with relative low intensity can be distinguished at R=120000;a set of reference compounds have been selected for providing accurate mass for the determination of unknown compounds with molecular weight ranging from 50–500 Da;(3)In addition to the compounds reported previously,sulfate,silicate,phosphate,nitrate,and dichlorobenzene have been detected in the mass range of m/z 50–300 in the breath,in which sulfate,silicate and phosphate are supposed to result from the aerosol particles in the exhaled breath while dichlorobenzene may be related to inhaled VOCs.Furthermore,29 compounds with relative high molecular weight compounds(300–500 Da)have been observed(the average ring-double bond equivalent(RDB)values is 4.5,implying a relatively high degree of unsaturation),which may contribute to a better understanding of the emission sources of exhaled VOCs as well as the ionization mechanism of SESI.