High-pressure Photoionization Mechanism Of Oxygenated Volatile Organic Compounds And Its Application

As an important class of environmental organic pollutants and metabolites of the human body,oxygenated volatile organic compounds?OVOCs?are widely distributed in the natural environment and anthropogenic activities.Therefore,the development of rapid and highly sensitive analytical methods for OVOCs is of great significance and broad prospects for environmental monitoring and auxiliary diagnosis of diseases.On-line mass spectrometry?MS?based on high-pressure photoionization?HPPI?source has the advantages of the fast analysis process,high sensitivity and low fragmentation.The ionizable range and ionization efficiency of compounds can be improved by employing different reactant ions for ion-molecule reactions with analytes.Therefore,the HPPI-MS is suitable for highly sensitive and rapid analysis of trace amounts of OVOCs.However,due to the influence of vacuum ultraviolet?VUV?photoionization and ion-molecule reactions with different reactant ions,the ionization mechanism of OVOCs in HPPI ion source is still unclear.Therefore,there is no perfect theoretical guidance for the analysis of mass spectra of complex mixtures.Based on a home-built HPPI time-of-flight mass spectrometry?TOFMS?platform,the ionization process and mechanism of OVOCs in HPPI source were studied.The main work and results are as follows:1.The HPPI process of OVOCs such as phenol and formaldehyde,as well as the effects of water molecules on their ionization process were studied.Based on the characteristic ions detected in the TOFMS of standard,the ionization process has been elucidated by combining its ionization power?IP?,proton affinity?PA?and other properties;2.The ionization process of toluene enhanced high-pressure photoionization?TE-HPPI?on phenol and other OVOCs has been investigated.Based on the response intensity of OVOCs at the same concentration and the change of characteristic ions detected by mass spectrometry,the mechanism of charge transfer reaction and proton transfer reaction between toluene reagent ions and various OVOCs has been demonstrated.Finally,based on the highly sensitive ionization of phenol by TE-HPPI source,it has been applied to the detection of phenolic compounds in sludge suspension;3.The effect of NO⁺enhanced high-pressure photoionization?NO-HPPI?on the ionization of low-weight aldehydes and alcohols has been studied as well as the effect of water molecules.The association of NO⁺and aldehyde organic compounds have been found.Co-use,and oxidation of alcohols under photoionization conditions.Finally,the NO-HPPI source was successfully applied to the detection of formaldehyde,acetaldehyde and acrolein in plastic samples;4.The effects of NO,toluene,chlorobenzene and halogenated CH_nX_?4-n??X=Cl or Br,n=1 or 2?reagent ions to diethyl ether,butyl acetate,propanol,methyl ethyl ketone,butyric acid and valeraldehyde on the photoionization process have been compared.It was found that both NO⁺and CH₂Br₂⁺can efficiently improve the protonated products of small molecule aldehydes.Besides aldehydes,NO⁺also can undergo association reaction with butyl acetate and methyl ethyl ketone.