Interpreting the gas chromatographic retention of n-alkanes

Non-linear regressions were applied to n-alkanes retention data for the determination of gas hold-up in a preceding paper. It was found that at temperatures over 100°C the reduced partial molar free energy of solution, ΔG/RT, tends to be negligible for the solute methane in poly(dimethylsiloxane) stationary phases. A consequence of interest can be inferred from this fact. The C–H bonds from terminal methyl groups of n-alkane solute molecules should not contribute significantly to ΔG/RT in these conditions. The analysis of data confirms that, within the chromatographic experimental error, the contributions of n-alkane end C–H bonds are also negligible in this temperature range. Consequently, the regression parameter that contains the phase ratio of the column only includes the gas hold-up as the accompanying factor.