Structures for lossless ion manipulation,
abbreviated SLIM, is a special low cost technique that utilitzes drift time ion
mobility. SLIM is a modular device, which allows different configuration and is
therefore able to manipulate ions in various ways among them storage, accumulation,
separation based on ion mobility, ion reactions and ion fragmentation. The
technique also implies a nearly 100% ion transmission independent from the duty
cycle applied ("lossless").
It is an ion optical device comprised on electrodes
patterned on planar surfaces. Specifically, it consists of two parallel stacked
circuit board (looks a bit like a sandwich) each having an array of DC guard
electrodes and an array of central rung electrodes having a DC with
superimposed RF similar to a conventional multipole.
Ion dynamics are similar to a multipole. Static
DC guard voltage confine the ions laterally and the dynamic RF/DC voltages of the rung electrodes create a pseudo
potential with a low energy region close to the central axis of the fly path to
maintain the ions close to the center.
Performance wise, the linear SLIM system at a
static pressure of 5-6mbar exhibits ion mobility resolution of 55 FWHM and is
capable of doing tandem IMS. Since IMS resolution in drifttube ion mobility for
a given ion pulse length and ion charge depends on length of drift tube, longer
SLIM devices may provide higher IMS resolution.
As previously mentioned the design is flexible
and it has proven to guide ions within different geometrical configurations
such as a 90°degree turn or a tee. Compared to measurements with the linear SLIM
configuration 90°degree turn configuration displayed similar IM resolution but
requires a greater confining confining RF amplitude and guard biases for overcome
the "racetack issue". The inventor from the Smith Lab introduced the
further development of the SLIM - SLIM 2.0 (good introductory video clip can be found here) - utilitzing travelling wave
technology last year. It's a pity I just have got to know it recently.
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