Chemical class information in ion mobility spectra at low and elevated temperatures

Mobility spectra for organic compounds at temperatures of similar to 50 deg reesC and 175-250 degreesC were categorized by chemical class using back-pr opagation neural networks with the successful classification even of chemic als not familiar to the networks. Network performance suggested that chemic al class information in spectra at similar to 50 degreesC differed from tha t in spectra at high temperatures, prompting a detailed analysis of regions where chemical class information was located. These regions, or drift time s in the mobility spectra, were identified at each temperature using a meth od of incrementally removing portions of spectra so that the value or struc tural content of the subtracted region could be seen in comparisons of netw ork performance. At high temperatures (175-250 degreesC), chemical class in formation was contained in fragment ions located in a narrow region of the spectra with reduced mobilities of 3.06-2.11 cm(2) V-1 s(-1) corresponding to the drift times near and encompassing the reactant ions peaks. In contra st, spectra at low temperature (similar to 50 degreesC) were classified thr ough fragment ions that resided in a broad region of drift time between pro tonated water clusters and product cluster peaks. This corresponded to redu ced mobilities of 1.8-1.2 cm(2) V-1 s(-1). These findings suggest that frag mentation in ion mobility spectrometry and other atmospheric pressure chemi cal ionization based methods, with moisture <1 ppm, may be more common than previously understood. Class specific fragmentation reactions for ions at low temperature have never been described in LMS and became evident only wh en mobility spectra were formatted with a logarithmic axis for ion intensit y. <(c)> 2001 Elsevier Science B.V. All rights reserved.