Suppression of gas species signals in direct current glow discharge time-of-flight mass spectrometry

Abstract

The possibility of suppressing gas species in direct current glow discharge mass spectrometry (dc-GDMS) with a linear time-of-flight mass analyzer was investigated. With this tic-GD ion source, a 'clean' mass spectrum rich in analyte could be obtained when the dc-GD was operated under a discharge current of 15-30 mA and a gas pressure of 300-500 Pa, in contrast to the strong signals of gas species in convention dc-GDMS, which operates at lower currents and pressures (typically 1-5 mA and 100 Pa). Such an experimental result is believed to be due to increased sputtering at higher pressures and currents, and the different ionization mechanisms of analyte and gas species. For a possible GD design to eliminate the background gas ions, a new discharge configuration was developed by attaching a TM,,, microwave resonator to the GD ion source. The mass spectrum of the cathode sample showed a low gas species background when the microwave-induced plasma (MIP) discharge was 'off' under different dc-GD parameters. The mass spectra of analyte and gas species obtained with 'MIP + dc-GD' and 'MIP only' modes are also compared and discussed. It was found that the analyte signals decrease and the gas species signals increase in the presence of the MIP, and that the analyte signals nearly disappear in the 'MIP only' mode. Preliminary results suggest that, for specific discharge conditions and with a suitable design of the GD source, an efficient suppression of gas species in dc-GDMS detection could be realized

Development and Evaluation of a Glow Discharge Microwave-Induced-Plasma Tandem Source for Time-of-Flight Mass Spectrometry

“…Interestingly, with this new GDMIP source and TOFMS detection, most of the background peaks of argon, nitrogen, and water species were found to drop significantly with microwave discharge boosting except for H 3 O . Such a result is significantly different from that observed in the GDMIP source using a TM 010 resonator . In addition, the influence of microwave boosting on the baseline noise level was also studied with the current system, and no significant difference in baseline noise level was observed with or without MIP supplement.…”

“…However, previous work on GDMIP was limited to coupling it to AES. − Exploration of coupling a GDMIP source with mass spectrometry may provide some further insights into the tandem source and its special analytical characteristics. Recently Su et al tested a TM 010 -based dc GDMIP tandem source for time-of-flight mass spectrometry (TOFMS) . Supplement of the MIP discharge seemed to boost the background ions only, and there was no significant enhancement of analyte signals .…”

“…Recently Su et al tested a TM 010 -based dc GDMIP tandem source for time-of-flight mass spectrometry (TOFMS) . Supplement of the MIP discharge seemed to boost the background ions only, and there was no significant enhancement of analyte signals . These results were believed due to an enhanced electron impact process near the vicinity of the sampler orifice and a reduced sputtering rate …”