where X, Mw, and M(n+1) are either the retention temperatures (or the adjusted retention times) of the unknown and straight-chain aliphatic esters.
The calculation of KI values starts with the injection of either a standard alkane mixture (C6 to C22) for Carbowax 20 M or DB Wax and (C6 to C30) for OV 101 or DB 5 (or linear ethyl esters) under the same linear programming temperature (2 to 4° C/min).
The software of the integrator can detect each peak and calculates each KI value automatically and prints it out with other GC data. All GC and GC/MS data are stored on a disk and visualized on a screen with the possibility to make a zoom on a wanted part of the chromatogram.
Kovats indices (or retention indices) have been compiled in various reviews, books, and many other publications (Jennings and Shibamoto, 1980; Swigar and Silverstein, 1981; Sadtler, 1985; Shibamoto, 1987; Davies, 1990; Adams, 1995, 2001). Another method for the calculation of Kovats indices has been suggested by Boniface et al. (1987) using scans (S) instead of retention times. A simple program called MBASIC.SCAN1 using the linear relationship:
has been used to calculate all KI of a listing. However, a prerequisite for this is to find at least 10 compounds for which the KI are known and which are uniformly distributed in the reconstructed chromatogram. The interest in KI is evident since on polar and nonpolar columns different compounds can give the same mass spectra (Vernin and Petitjean, 1982; Vernin et al., 1986). KI of sesquiterpene hydrocarbons have also been reported by Andersen et al. (1969, 1970, 1973, 1977) and Joulain and Koenig (1998). KI as a preselection routine in mass spectra library searches of flavor and fragrance volatiles have been used by many workers (Alencar et al., 1984; Yamada et al., 1987; Vernin et al., 1986, 1998). Furthermore, these indices possess a number of properties that can be suitable as a route of identification. Differences between KI (DKI) on polar and nonpolar columns are characteristic of a particular family of compounds. They have been summarized by Vernin et al. (1998). Modern GC/MS techniques can also be used to obtain more information about either a series of compounds or on molecular weights of unknown compounds.
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