Direct Measurement of Aromatic Compounds in Aqueous Solution by Laser Ionization/Time-of-Flight Mass Spectrometry

Laser ionization/time-of-flight mass spectrometry (LI/TOF-MS) is a selective analytical means for the measurement of aromatic hydrocarbons in the gas phase. In the present study, a simple and sensitive method was developed for direct measurements of species in an aqueous solution. A volatile 2,4-xylenol in aqueous solution was directly detected by using an ionization laser emitting at 266 nm. Moreover, when a vaporization laser emitting at 532 nm was irradiated into the tip of the capillary column, a signal enhancement of the analyte was achieved; even without a frit, the molecules could be introduced into a vacuum chamber in a pulsed form. Furthermore, using a narrow capillary column (e.g., inner diameter 25 pm) as an inlet nozzle as well as using a vaporization laser, the aqueous solution was smoothly introduced into the vacuum system; then, the fluctuation of the signal intensity for the analyte was reduced. On the other hand, a low-volatile phenylalanine in an aqueous solution could be detected when the ionization laser was adjusted to the tip of the capillary. The present method has potential for use in the sensitive, selective and real-time monitoring of aromatic compounds in environmental water samples and in culture media.