Role of Pressure Gradients in obtaining Minimum Time in Gas Chromatography

ALTHOUGH a great deal of attention1–5 has been focused on obtaining separations in the least possible time, the theory of minimum-time operation has not been developed for inlet/outlet pressure ratios greatly exceeding unity. Such a theory does not immediately seem widely applicable since most rapid separations made with an outlet pressure of one atmosphere do not require an inlet pressure greatly exceeding one atmosphere. This conclusion is incorrect, however, since a search for the optimum values of all parameters reveals that the optimum outlet pressure is very close to zero in all circumstances. Furthermore, the difference in minimum retention times found with an outlet pressure of one atmosphere and zero is large enough in many cases to be significant in obtaining more rapid analyses.