Minimum analysis time in capillary gas chromatography. Vacuum- versus atmospheric-outlet column operation

Previous studies on open tubular column operation at vacuum outlet vs. atmospheric outlet pressures focused on comparisons of given columns, or comparisons of columns with the same inner diameters. It was demonstrated that, for a given separation problem, vacuum outlet operation of columns with a constant i. d. always yields the shortest analysis times (under minimum plate height conditions). In this paper, the comparison of vacuum vs. atmospheric outlet operation is broadened to columns with different dimensions. A general equation for the gain in speed of analysis by vacuum outlet operation of any column, as compared to atmospheric outlet operation of all possible open tubular columns with the same maximum plate number is presented. The resulting equation is further evaluated for thin film columns of different dimensions. It appears that vacuum outlet operation is beneficial only, in terms of speed of analysis, if low maximum plate numbers are required. The gain in speed of analysis is more pronounced for wide-bore than for narrow-bore columns