Liquid Chromatography/Dopant-Assisted Atmospheric Pressure Chemical Ionization Mass Spectrometry (LC/DA-APCI-MS) for the Analysis of Non-Polar Compounds

摘要

Liquid chromatography dopant-assisted atmospheric pressure chemical ionization mass spectrometry (LC/DA-APCI-MS) has been explored and proven as a reliable method for the analysis of non-polar compounds. Polycyclic aromatic hydrocarbons (PAHs) were analyzed as non-polar representatives. They were ionized through charge exchange reactions with the dopant radical ions. Chlorobenzene, toluene and anisole were explored as a dopant with anisole achieving the best results. Due to its lower ionization energy (IE), anisole generated substantially more radical ions than chlorobenzene. Anisole's radical ions were also found to be more stable and longer-lived than the radical ions of toluene. In addition, anisole generated much less intense chemical background ions at m/z<=250 than both chlorobenzene and toluene. With anisole as the dopant, the LODs of PAHs has been improved up to two orders of magnitude in comparison to LC/APCI-MS. Furthermore, the best LOD achieved was equivalent to that achieved in the analysis of reserpine by LC/APCI-MS, implying that the analysis of non-polar compounds by LC/DA-APCI-MS has the potential to be as successful as the analysis of polar compounds by LC/APCI-MS. In comparison to LC/DA-APPI-MS, LC/DA-APCI-MS possibly generated more chemical background ions at m/z <= 250, which prevented the improvement of PAH ionization efficiency by the use of high dopant flow rates for compounds with m/z <= 250. In addition, ionization of the LC solvents promoted the formation of solvent adducts, i.e. [M + CH_(2)CN]~(+) ions, for a few PAHs.