Retention index interpolation using temperature

A first prediction attempt of GCxGC retention using this strategy was carried out by Beens et al. [10]. Retention times in the D column were calculated from those of n-alkanes and the analyte retention index. For the analyte retention times in D, k was first obtained by interpolation for the n-alkane series at the elution temperatures, the retention times f of these compounds were calculated using the corresponding holdup times, and then t Ri for the analyte was calculated from its RI at the elution temperature using Equation (3). Differences between calculated and experimental values were observed for D retention times, although predicted elution profiles were similar to the experimental patterns. A similar approach [27] used k values measured at several temperatures to obtain a better interpolation. The accuracy of the prediction of retention times was... 

The retention index is calculated by logarithmic interpolation between consecutive alkanes and the data acquired under isothermal analysis conditions. Under linear temperature programming, however, an almost identical system of expressing retention data is the methylene unit concept in which methylene unit (MU) values are determined by linear interpolation between the /i-alkanes eluted before and after the compound (Dalgliesh etal, 1966). For example, a peak eluted midway between C19 and C20 under these conditions would have a MU value of 19.50 and an equivalent retention index calculated from this of approximately 1950. The interrelation of isothermal and temperature-programmed data for a particular type of phase, even under widely different analytical conditions, is possible and both concepts permit very useful comparisons of different sets of available literature data. Relative retention times, on the other hand, can show fairly wide variations in values, especially with regard to temperature, and are less suited for use as literature reference data. 

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