Linearized Equations for the Reduced Ion Mobilities of Polar Aliphatic Organic Compounds Chandrasekhara B. Hariharan,* Jo ¨ rg I. Baumbach, and Wolfgang Vautz ISAS - Institute for Analytical Sciences, Bunsen-Kirchhoff-Strasse 11, 44139 Dortmund, Germany Over the years, ion mobility spectrometry has evolved into a powerful technique for rapid identification of analytes in very complex sample matrixes such as human breath. Every analyte detected has a characteristic ion mobility value (and a retention time when additional preseparation techniques are employed) which is used to identify the peaks in a spectrum either by comparison with reference analytes or by simultaneous mass spectrometric mea- surements. In this study, the mass-mobility correlations between compounds in three different homologous series are used to predict the mobilities of the other substances in the same series in a medium of synthetic air. The results show a very high accuracy (>99.5%) of the prognosis. The linear trend equations of ion mobilities, as a function of the number of carbon atoms, obtained from the different series were then generalized into one linear equation for the reduced ion mobility for the polar aliphatic compounds and is validated by comparing it with the traditional Mason-Schamp equation. To compare the empirical equation obtained from the prognosis and the Mason-Schamp equation, the collision integral term in the latter was split into two terms to linearize it. The resulting novel ion mobility equation could be the starting step to completely describe the relationship between ion collision integral and the ion mobility for polar aliphatic compounds. The splitting of the collision integral into two terms will also give new inputs to describe the various ion models and the different forces that act on the ions and the neutral gas molecules upon which the collision integral is dependent on. This prognosis method could, furthermore, be extended to all other classes of organic compounds and could serve as a useful tool for identifica- tion of unknowns in ion mobility spectra, thereby consid- erably reducing the time-consuming and costly reference measurements and other coupling techniques that are currently employed. Ion mobility spectrometry is an inexpensive and powerful analytical technique used for rapid detection of gas-phase samples in the lower ng L -1 (ppb v ) down to pg L -1 (ppt v ) levels at ambient pressures and temperatures. 1,2 Although the principles of ion motion in an electric field were explained as early as 1903 by P. Langevin, the instrumentation of an ion mobility spectrom- eter was developed much later in the late 1960s and early 1970s. 1,3 Ion mobility spectrometers (IMS) were initially used for direct monitoring of specific compounds classes such as chemical warfare agents, explosives, and drugs of abuse. 1-3 However, in recent years, due to its high sensitivity, information density and relatively low technical costs, they are being used for newer applications, specifically on biological samples, medical diagnosis, and process control. 4-21 These applications face challenges such as humid and rather complex sample matrixes, requirement of specific sampling procedures for each application, fast presepa- ration techniques, different data preprocessing steps, and most importantly, suitable data processing techniques that include reliable and accurate databases of relevant analytes for automatic identification of the signals detected in an IMS chromatogram. 22-31 * Corresponding author. 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