Separation principle and Monte Carlo studies for differential mobility spectrometry
Separation principle and Monte Carlo studies for differential mobility spectrometry
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DOI：
10.1007/s12127-011-0083-8
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发表时间：
2012-09
影响因子：
--
通讯作者：
Jun Xu;Fenglei Han;Haiyang Li
中科院分区：
文献类型：
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作者：
Jun Xu;Fenglei Han;Haiyang Li
Since its first publication in 1991 [1], differential mobility spectrometry (DMS), also known as field asymmetric ion mobility spectrometry (FAIMS), is increasingly used as an analytical method, either as stand-alone detectors of trace chemicals or as selective filters for mass spectrometry (MS)[2–6]. In conventional ion mobility spectrometry (IMS), ions are separated according to their mobility. Differing from IMS, DMS separates ions by the difference of ion mobilities generated in high-and low-fields. This difference is directly related to non-linear mobility coefficient, α, which is dependent of driving electric field during ion transport [7–13] and to ion identity. Measuring such differential mobility constitutes a separation method. DMS functions generally in the following manner: Ion species transport under an longitudinal gas flow passing through a narrow filtration gap formed between two parallel electrodes. A transverse, asymmetric RF potential is applied between the electrodes, generating periodic alternating highand low-electric fields in the gap. The alternating fields cause ions to move inside the gap with seesaw trajectories in average. In the high-field phase, nonlinear mobility coefficient, α, becomes dependent on the ratio (E/N) of the electric field to the carrier gas density. In the low-field phase, α is independent of the field. Therefore, a net displacement toward either electrode of the gap is generated during one cycle of the asymmetric RF waveform. Since different type of ions experiences a different net displacement, the ion can be separated by adjusting the bias between the two electrodes to compensate the displacement, namely compensation voltage, VC. In this work, we examine the relation between nonlinear mobility coefficient, α, and the compensation voltage.In our previous work Monte-Carlo simulation of ion trajectories in DMS [13] was reported. However, the previous simulation was restricted by three conditions. First the RF asymmetric waveform was a square function, which is hardly used in practical DMS spectrometers. Second, ion clustering in low electric field and declustering in high electric field, which result in different ion identities, were not considered. Third, polarization effects were not considered. Due to these limitations, it was difficult to compare Monte-Carlo simulation result with experimental data. In this work, we considered a more realistic waveform used in DMS experiments, field-induced clustering and de-clustering, and the effect of polarization on the cross section calculation. In order to compare with simulated results, some specific DMS experiments were done for typically known reactant ions, H+(H2O) n.
