Optimal heating rate in constant pressure and constant flow gas chromatography

Optimal heating rate is the one resulting in the shortest analysis time for achieving a required separation performance of a column. The previously recommended default heating rate (R_T,Def ) was optimal for temperature-programmed gas chromatography analyses in constant pressure mode. It has been shown herein that the same recommendation can be extended to constant flow mode with fixed heating rate (R_T ). The numerical value of R_T,Def has been herein rescaled from previous $$ (10°C per void time) where t_M was measured at 50°C, to $$ with t_M measured at 150°C-a round number in the middle of the gas chromatography temperature range, chosen as a reference temperature for numerical values of all temperature-dependent gas chromatography parameters. It has been experimentally found based on theory developed herein that $$ is optimal for columns with $$ ( $$ is dimensionless film thickness, d and d_f  are the column internal diameter and film thickness, respectively) in constant pressure mode and constant flow mode with fixed R_T . Theory shows that, for arbitrary φ, $$ . The theory also shows that the fixed R_T is optimal for constant pressure mode. In constant flow mode, however, the optimal R_T should gradually increase with increasing temperature (T). The optimal theoretical curves R_T (T), different for different flow rates, were found. However, only the optimization of the fixed R_T was experimentally evaluated due to limited capability of existing gas chromatography instrumentation and resources. It has been shown that the separation-time tradeoff in constant pressure mode is slightly better than that in constant flow mode. The experimental data are compiled in the Supporting information.