Nanosecond Pulsed Dielectric Barrier Discharge Ionization Mass Spectrometry

Dielectric barrier discharge ionization (DBDI) is an emerging technique for ionizing volatile molecules directly from complex mixtures for sensitive detection by mass spectrometry (MS). In conventional DBDI, a high frequency and high voltage waveform with pulse widths of ∼50 μs (and ∼50 μs between pulses) is applied across a dielectric barrier and a gas to generate "low temperature plasma." Although such a source has the advantages of being compact, economical, robust, and sensitive, background ions from the ambient environment can be formed in high abundances, which limits performance. Here, we demonstrate that high voltage pulse widths as narrow as 100 ns with a pulse-to-pulse delay of ∼900 μs can significantly reduce background chemical noise and increase ion signal. Compared to microsecond pulses, ∼800 ns pulses can be used to increase the signal-to-noise and signal-to-background chemical noise ratios in DBDI-MS by up to 172% and 1300% for six analytes, including dimethyl methylphosphonate (DMMP), 3-octanone, and perfluorooctanoic acid. Using nanosecond pulses, the detection limit for DMMP and PFOA in human blood plasma can be lowered by more than a factor of 2 in comparison to microsecond pulses. In "nanopulsed" plasma ionization, the extent of internal energy deposition is as low as or lower than in electrospray ionization and micropulsed plasma ionization based on thermometer ion measurements. Overall, nanosecond high-voltage pulsing can be used to significantly improve the performance of DBDI-MS and potentially other ion sources involving high voltage waveforms.