Sensitive low-pressure dielectric barrier discharge ion source.

Rationale: We developed a novel highly sensitive soft ionization method: a low-pressure dielectric barrier discharge ionization (LP-DBDI) source. In this configuration, samples pass through the inside of a dielectric barrier discharge (DBD). Since samples pass through a DBD and its plasma jet, high ionization efficiency is expected. Furthermore, high transmission efficiency from the ion source to the mass spectrometer is also expected since the ion source is placed in a vacuum.

Methods: Mass spectrometric detection was carried out in positive ion mode using an ion trap mass spectrometer. The LP-DBDI source or a conventional atmospheric pressure chemical ionization (APCI) source was attached to the mass spectrometer. Samples were vaporized and sent to ion sources with air flowing at a constant flow rate of 1.5 L/min. The LP-DBDI source was compared with a conventional APCI source.

Results: Mass spectra of methyl salicylate, 2-undecanone and methamphetamine were acquired using the LP-DBDI source. Protonated molecules were mainly observed in the mass spectra. The sensitivities for methyl salicylate and 2-undecanone obtained using the LP-DBDI source were 44 times and 39 times higher, respectively, than those obtained using an APCI source.

Conclusions: LP-DBDI is a soft ionization method characterized by only minor fragmentation, similar to APCI. The sensitivity of the LP-DBDI source was found to be about 40 times higher than that of the conventional APCI source.