Development Of A Quantitative Analysis Method For Eight Volatile Organic Compounds In Breath Based On Secondary Electrospray Ionization High Resolution Mass Spectrometry

The secondary electrospray ionization source coupled with high resolution mass spectrometry is a direct mass spectrometry technology that can be used to detect volatile organic compounds(VOCs)in the breath in real time,such as aldehydes and ketones,organic acids,unsaturated hydrocarbons,etc.At present,it has been successfully applied to the research of chronic obstructive pulmonary disease diagnosis,circadian clock and drug metabolism.However,due to the lack of a SESI-HRMS quantitative analysis method for VOCs in exhaled breath,the popularization and standardization of the SESI-HRMS method was limited.In this study,a mixture standard gas containing ketones(acetone,2-butanone and 2-pentanone),alkenes(isoprene,α-terpinene)and aromatics(toluene,styrene and mesitylene)was used for the development of a quantitative method using SESI-HRMS.The mixture standard gas was diluted online to a series of concentrations by a gas dilution calibrator,and then detected in real time by a commercial Super SESI source coupled with a quadrupole orbitrap high-resolution mass spectrometer.The SESI-HRMS quantitative analysis method of eight VOCs in exhaled breath was established,and the quantitative analysis method was applied to the quantification of VOCs in exhaled breath and the evaluation of the recovery of varies sample storage and sampling processes for exhaled VOCs.The most important results are presented as follows:(1)The linear range of acetone,2-butanone,2-pentanone,isoprene,α-terpinene,toluene,styrene and mesitylene were 0～10 ppbv,the LODs of eight VOCs varied from 3 to 15 pptv,and the intra-day and inter-day precision were ≤ 6% and ≤ 10%,respectively.The results indicate satisfactory stability and reproducibility were obtained by using the present method.It was also found that for each type of compounds,the sensitivity increases with increasing mass.Interestingly,the sensitivity increases with increasing proton affinity(PA)for ketones and alkenes;however,for benzene series,the sensitivity of mesitylene is about ten times higher than that of styrene even though the PA of mesitylene is slightly lower than that of styrene,this implies that the ionization mechanism of SESI may not be limited to proton transfer reaction,which provides ideas for later SESI mechanism research.(2)The method was applied to the quantitative analysis of VOCs in exhaled breath of 10 healthy subject.The average concentrations of acetone,isoprene,α-terpinene,toluene,styrene and mesitylene were 14 ppbv,730 pptv,410 pptv,1 ppbv,88 pptv and 14 pptv,respectively.The recoveries of mixed standard gas stored in three typical gas sampling bags showed that the recoveries using PTFE gas sampling bags were the highest;and significant adsorption was observed for toluene in Nalophan and Tedlar gas sampling bags.In the Nafion tube experiment,it was observed that the recoveries of 2-pentanone,α-terpinene,toluene,styrene and mesitylene were lower than 50% while they were delived in a Nafion tube.Thus,Nafion tube is not suitable for the delivery of these five VOCs.Meanwhile,we also found that for each type of compounds,compounds with higher molecular weight have shown higher loss in the Nafion tube.