The maximum electric field intensity (E) in field asymmetric waveform ion mobility spectrometry (FAIMS) analyses was doubled to E > 60 kV/cm. In earlier devices with >0.5 mm gaps, such strong fields cause electrical breakdown for nearly all gases at ambient pressure. As the Paschen curves are sublinear, thinner gaps permit higher E: here, we established 61 kV/cm in N 2 using microchips with 35 μm gaps. As FAIMS efficiency is exceptionally sensitive to E, such values can in theory accelerate analyses at equal resolution by over an order of magnitude. Here we demonstrate FAIMS filtering in ~20 μs or ~1% of the previously needed time, with a resolving power of about half that for "macroscopic" units but sufficing for many applications. Microscopic gaps enable concurrent ion processing in multiple (here, 47) channels, which greatly relaxes the charge capacity constraints of planar FAIMS designs. These chips were integrated with a β-radiation ion source and charge detector. The separation performance is in line with first-principles modeling that accounts for high-field and anisotropic ion diffusion. By extending FAIMS operation into the previously inaccessible field range, the present instrument advances the capabilities for research into ion transport and expands options for separation of hard-to-resolve species.Ion mobility spectrometry (IMS) distinguishes ion species based on transport properties in an inert buffer gas. Conventional or drift tube (DT) IMS that separates ions based on absolute mobility has been used in defense and security applications in the field, such as detection of explosives and chemical warfare agents, since the 1980s. 1 More recently, IMS (combined with mass spectrometry, MS) became topical in structural chemistry and in complex biological and environmental analyses. [1][2][3][4][5][6][7][8][9][10][11] The mobility for any ion-gas pair is a function of the ratio of electric field intensity (E) to the gas number density (N), which can be expressed 2 as a relative deviation (α) from the zero-field mobility K(0) and expanded in infinite series of even powers over E/N:This fact is exploited in differential IMS or field asymmetric waveform IMS (FAIMS) to filter ions by the difference between K at two E/N values. 2,3 A time-dependent electric field E(τ) with alternating segments of high E and low E of opposite polarity (but null mean E) is set up in a gap between two electrodes, through which ions are pulled by gas flow. 2,3 HypotheticalCorrespondence to: Alexandre A. Shvartsburg.

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