Consistency of gas hold-up determinations

Abstract

The retention of methane on poly(dimethylsiloxane) capillary columns was studied focusing its relation with the gas hold-up time t M, which was derived from the retention of n-alkanes. The [ideal gas/Van der Waals fluid] partition equation was applied in order to provide the mathematical expression for the retention factor of the n-alkanes as a function of the carbon number n. In this context the partial molar free energy of solution is a non-linear function of the chain length Δ G s( n) ( n≥5). The resultant retention factor k of methane, determined from its retention time and the calculated t M, approaches an almost constant value when the temperature is increased beyond 100°C. This value of k has the order of the reciprocal column phase ratio 1/ β. Precisely, this is the theoretically expected limit of a non-interacting solute or inert marker.