溶媒–メタン混合系試薬ガスを用いる化学イオン化質量分析法の基礎的検討

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To obtain useful CI mass spectra, several kinds of solvents with methane have been introduced into a Finnigan 3300E-GC/QMS CI ion source via its direct introduction portion by means of a micro LC pump for utilization as reagent gas. With solvent alone, the pressure of the ion source and the analyzer could not be kept under control at any condition, but addition of methane from the GC carrier gas line enabled the pressure to stabilize as well as increasing the reactant ion abundance by a several to ten fold magnitude or even more. The optimum ion source condition for this method was as follows, solvent flow rate: 0.8μl/min (corresponding to 0.05~0.1 Torr), total pressure of ion source with methane: 1.0 Torr, ion source temperature: 70°C. It was found that methane mainly functioned as a proton donor in the methane mixture system. In complex system containing more than two solvents, ions derived from those possesing the highest proton affinity became dominant reactant ions except the non polar solvents such as n-hexane. Because of its high proton affinity, ammonia often acted as a terminal proton acceptor resulting in NH4+ as the dominant reactant ion within the ammonia containing system, thus enabling constant ionization. The proposed method facilitated acquisition of plural CI mass spectra in GC/MS mode using several solvents. An on-off cock situated on line with the direct introduction portion enabled measurement of plural CI mass spectra within a GC peak. The usage of deuterium oxide as reagent gas enabled determination of active hydrogen of unknown samples without deuteration pretreatment and identification of isomers such as N-methylaniline and o-toluidine difficult to be distincted by EI, CI (CH4) or CI (i-C4H10) mode.
日本質量分析学会の論文

溶媒–メタン混合系試薬ガスを用いる化学イオン化質量分析法の基礎的検討

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