Mass Spec Master: SLIM 2.0 - Structure for lossless ion manipulation

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.