General model for precalculation of the retention indices of isoalkanes separated by gas or liquid chromatography

A general model consisting of two terms is proposed for precalculation of retention indices of isoalkanes separated by gas chromatography (GC) on a squalane column and by high-performance liquid chromatography (HPLC) on a column containing a bonded octadecyl phase. The first term (referred to as extensive) includes parameters which have the greatest correlation with the experimental value of the index; the second term (referred to as intenzive) includes parameters which can modify the value of the roughly calculated index in the direction of the experimental value. The equations derived have correlation coefficients better than 0.99. The maximum discrepancy between the experimental and calculated retention index for twenty C₆C₈ isoalcanes was less than ± 1 index unit in gas chromatography and less than 4 index units in HPLC. The retention indices of 23 other C₇C₉ isoalkanes, calculated in the extrapolation region of the equations, were sufficiently accurate.