Nonlinear variation of sorption parameters of n-alkane homologs in temperature-programmed gas chromatography (TPGC) and new equation for calculation of retention indices

It has been demonstrated that the considerable difference in temperature increments of sorption parameters of n-alkanes under isothermal conditions is the main reason for nonlinear dependence of sorption parameters on molecular mass of homolog in temperature programmed gas chromatography (TPGC). A new nonlinear 4th parameter equation has been given for calculation of the retention indices. Coefficients of the equation are calculated from n-alkanes. The equation allows extrapolation and interpolation calculations of retention indices under TPGC conditions with experimental precision. The results obtained for fatty acid methyl esters demonstrate the advantage of our equation in comparison with van den Dool and Kratz's equation.