Ion mobility mass spectrometer (IMS)
Smiths Detection
Ion Mobility Spectrometry, or IMS, is an instrumental analytical method that is similar to Time-of-Flight MS. Instead of responding to molecular fragments, however, IMS uses soft ionization. Ionized molecules travel through a drift tube at distinct speeds that are related to their mass and geometry. Selectable positive and negative ionization enhances identification or sensitivity.
The ions in question are generated by atmospheric-pressure chemical ionization. Sample material is heated to yield a vapor that is swept into a small drift chamber where a beta radiation source ionizes the molecules. The resulting ions - separated according to size, mass and geometry - accelerate towards a detector.
On impact, each ion generates a specific signal, which is a function of ion mobility. Mobility (K) is determined from the drift velocity (vd) attained by ions in a weak electric field (E) in the drift tube, according to the equation, vd = K x E. The distribution of these signals forms an ion spectrum, with an ion mobility band corresponding to each of the unique ionic species. The spectrum is a fingerprint of the parent compound. Libraries of these ion spectra remain resident in the IONSCAN software and are in the screening process.
