Consistency of gas hold-up determinations

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 Delta G(s)(n) (n greater than or equal to 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 degrees C. This value of k has the order of the reciprocal column phase ratio 1/beta. Precisely, this is the theoretically expected limit of a non-interacting solute or inert marker. (C) 1999 Elsevier Science B.V. All rights reserved.