School of Chemistry, University of New South Wales, Sydney, New South Wales, Australia.
School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia.
Anal Chem. 2020 Mar 17;92(6):4468-4474. doi: 10.1021/acs.analchem.9b05491. Epub 2020 Mar 2.
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.
介质阻挡放电电离（DBDI）是一种新兴的技术，可直接将复杂混合物中的挥发性分子离子化，用于质谱（MS）的灵敏检测。在传统的 DBDI 中，应用在介电层和气体之间的高频高压波形的脉冲宽度约为 50 μs（脉冲之间的间隔约为 50 μs），以产生“低温等离子体”。尽管这种源具有体积小、经济、坚固和灵敏的优点，但来自环境的背景离子可以以高丰度形成，这限制了其性能。在这里，我们证明，脉冲宽度窄至 100 ns、脉冲到脉冲的延迟约为 900 μs 的高压脉冲可以显著降低背景化学噪声并增加离子信号。与微秒脉冲相比，在 DBDI-MS 中，约 800 ns 的脉冲可以将信号与噪声和信号与背景化学噪声的比值提高高达 172%和 1300%，用于六种分析物，包括二甲基甲基膦酸酯（DMMP）、3-辛酮和全氟辛酸。使用纳秒脉冲，与微秒脉冲相比，DMMP 和 PFOA 在人血浆中的检测限可以降低两个数量级以上。在“纳秒脉冲”等离子体电离中，内部能量沉积的程度与基于温度计离子测量的电喷雾电离和微脉冲等离子体电离一样高或更低。总体而言，纳秒高压脉冲可以显著提高 DBDI-MS 的性能，并可能提高其他涉及高压波形的离子源的性能。
