Evaluation of a glow discharge chamber coupled to time of flight mass spectrometry for the analysis of small gas volumes and bubbles in glass

Abstract

Glow discharge time-of-flight mass spectrometry (GD-TOFMS) is becoming a powerful tool not only for simultaneous elemental determinations but also for possible molecular analysis of solid and gaseous samples. In this work, a modified in-house GD ion source, operated with radiofrequency (rf) power and coupled to an orthogonal TOFMS, is investigated for the analysis of small volumes of gaseous samples. Moreover, the results are compared with those obtained using a previous GD source design containing an internal flow tube. The modified in-house GD ion source has a reduced internal volume and no flow tube built in, allowing the use of lower gas flow rates. Additionally, this design allows the GD source to be placed closer to the sampler cone of the MS, resulting in improved ion transport efficiency. Limits of detection obtained for the analysis of small volumes of gas, turned out to be more than one order of magnitude better when using this modified in-house GD ion source. Furthermore, the pulsed mode of the rf-GD system (both, in millisecond and microsecond regimes) has been investigated to further improve the analytical performance of the technique for small gas volumes analysis. Calibration curves are obtained for the selected molecular compounds including nitrogen, oxygen and carbon dioxide. The results show that the limits of detection can be further improved by using a 100 μs-pulsed-rf-GD-TOFMS system, where limits of detection observed were below nanolitre for molecular nitrogen and oxygen, and below picolitre for carbon dioxide.