Gas chromatographic-ion trap mass spectrometric analysis of volatile organic compounds by ion-molecule reactions using the electron-deficient reagent ion CCl_3~+

摘要

When using tetrachloromethane as the reagent gas in gas chromatography-ion trap mass spectrometry equipped with hybrid ionization source, the cation CCl_3~+ was generated in high abundance and further gas-phase experiments showed that such an electron-deficient reagent ion CCl_3~+ could undergo interesting ion-molecule reactions with various volatile organic compounds, which not only present some informative gas-phase reactions, but also facilitate qualitative analysis of diverse volatile compounds by providing unique mass spectral data that are characteristic of particular chemical structures. The ion-molecule reactions of the reagent ion CCl_3~+ with different types of compounds were studied, and results showed that such reactions could give rise to structurally diagnostic ions, such as [M+CCl_3 - HCl]~+ for aromatic hydrocarbons, [M - OH]+ for saturated cyclic ether, ketone, and alcoholic compounds, [M - H]~+ ion for monoterpenes, M.+ for sesquiterpenes, [M - CH_3CO]~+ for esters, as well as the further fragment ions. The mechanisms of ion-molecule reactions of aromatic hydrocarbons, aliphatic ketones and alcoholic compounds with the reagent ion CCl_3~+ were investigated and proposed according to the information provided by MS/MS experiments and theoretical calculations. Then, this method was applied to study volatile organic compounds in Dendranthema indicum var. aromaticum and 20 compounds, including monoterpenes and their oxygen-containing derivatives, aromatic hydrocarbon and sesquiterpenes were identified using such ion-molecule reactions. This study offers a perspective and an alternative tool for the analysis and identification of various volatile compounds.