Differential Mobility Separation of Ions Using a Rectangular Asymmetric Waveform

Abstract

The performance of a planar differential mobility spectrometer (DMS) is investigated when operated in air at ambient pressure and driven by a rectangular asymmetric waveform, limited to frequencies of <1.2 MHz and voltage pulse amplitudes of <1 kV with steep rise times of the order of approximately 15 ns. Independent control of frequency, voltage pulse amplitude, and duty cycle allow for characterizing the DMS in terms of transmission, resolution and separation. The tradeoff between sensitivity and resolution and the effect of duty cycle on instrument performance are demonstrated experimentally. The dependence of ion mobility on the magnitude of the electric field determines the displacement of ions measured by the DC compensation voltage as a function of the duty cycle. Optimum values for the duty cycle exist for the separation of A- and C-type ions, while, B-type ions exhibit a more complex behavior. An analytical expression for describing the effect of duty cycle on the separation of the ions, determined by variations in the compensation voltage, is developed and compared to experimental results obtained in air below 75 Td using estimated alpha parameters for a set of ketones. In this context, errors associated with the calculation of alpha parameters using polynomials of even powers are highlighted.

Optimum waveforms for differential ion mobility spectrometry (FAIMS)

“…The trends of eqs 12 and 15 were verified by measurements [40,50], producing f opt ϳ2 with constant E D and ϳ3.7 with constant E P-P . Constraints on both E P-P and E D lead to 2 Ͻ f opt Ͻ 3.73.…”

FAIMS Biochemical Sensor Based on MEMS Technology

“…In this way the ion loss due to collisions with the electrode becomes larger, and the ion signal intensity decreases, thus the resolution increases. It was shown from theoretical formula that the frequency change does not affect the value of compensation voltage (Papanastasiou et al, 2008). When the square wave radio frequency voltage amplitude is 320V, the duty ratio is 30%, and the frequency is 2MHz, the flow velocity of the carrier gas increases from 0.6L/min to 1.4L/min.…”

“…We can see from figure 32 that with an increase in the amplitude of the square wave radio frequency voltage, the compensation voltage value (absolute value, same as below) will increase and the ion signal intensity will fall. The ion mobility of the 2-pentane will increase with increasing electric field intensity (Papanastasiou et al, 2008). So with increasing voltage amplitude, the amplitude of the ion will increase under the effect of the high electric field, the net displacement in one cycle will increase, and the compensation voltage for reverse compensation on the net displacement will also increase.…”

Uniform Moment Theory for Charged Particle Motion in Gases

“…The principles of operation of such devices with parallel plate geometry were described by Buryakov et al [40]. The use of concentric cylinders for FAIMS was advocated by Guevremont and Purves [41], in order to avoid difficulties in working with a rectangular asymmetric waveform [42].…”