Gas chromatography at finite concentrations. Part 4.—Experimental evaluation of methods for thermodynamic study of solutions

Abstract

Activity coefficients of n-hexane in squalane, and of n-heptane in di-n-nonyl phthalate, at 30°C, have been measured gas-chromatographically over the ranges of mole fractions of dissolved solute 0–0.7, and 0–0.5, respectively. Results obtained by the three GC methods of FACP, FA and EP agree with each other and with results from previous static measurements to well within the precision of the data over the ranges of concentration quoted. This finding validates the theory of finite concentration GLC already derived. Experimental requirements for accurate results are discussed, in particular the need for very small solute peaks in EP, and for monitoring the input boundary profile in FA and FACP. The influence of chromatographic nonideality (kinetic band-broadening processes) on boundary profiles affects the accuracy of FACP results to only a small extent. The respective merits and demerits of the various techniques are compared. GC techniques are strongly competitive, in speed and accuracy, with static gravimetric methods.