Kwang S. Yun

Repetitive liquid injection system for inverse gas chromatography

Abstract A hybrid injection system composed of a closed-loop vaporization chamber with a gas sampling valve is described. The system allows liquid injection into the vaporization loop with subsequent multiple injections of the vaporized solute(s) via the gas sampling valve (GSV). Very small amounts of probe solutes can be injected without a dilution solvent, and the vaporization loop acts as a “retention gap” for capillary columns. The use of a pneumatically controlled valve injector provides very accurate and reproducible injection volumes at precise time intervals. Combination of precisely timed injections with temperature programming of the column oven produces continuous chromatograms and retention data at controlled temperature increments. The proposed injection system eliminates the need for split injectors; it is cleaner than normal in-line injectors because nonvolatile samples cannot reach the column; and the instrumentation is easily automated. The major disadvantages are the restriction that the samples must be volatile at temperatures lower than the upper temperature limit of the valve rotor; the GSV is susceptible to both contamination and mechanical failure; the sample can be exposed to metal components of the valve; and initial distribution of the sample throughout the closed-loop vaporization chamber may be slow.

Theoretical Investigation of the excess free energy of binaryn-alkane systems

Abstract It is shown that the recent theory of Janini and Martire can be used to interpret the infinite dilution activity coefficients of 36 binaryn-alkane systems at 80, 100, and 120 C, and activity coefficients as a function of mole fraction for threen-alkane systems.

Experimental method to distinguish column dead time from system dead time for the accurate determination of gas chromatographic void volumes: simultaneous pre- and post-column injection

A new experimental technique for the accurate determination of the dead time of a chromatographic column is described. The technique involves simultaneous pre- and post-column injections of an unretained probe solute. The method allows the accurate determination of the column void volume as opposed to the system void volume which includes extracolumn volumes. The procedure also eliminates the uncertainties in void volume measurements caused by splitters, multiple flow paths, or auxiliary gas flows required for some detectors or certain types of chromatography such as supercritical fluid chromatography.

Lattice–fluid model for gas–liquid chromatography

Lattice-fluid models describe molecular ensembles in terms of the number of lattice sites occupied by molecular species (r-mers) and the interactions between neighboring molecules. The lattice-fluid model proposed by Sanchez and Lacombe (Macromolecules, 1978;11:1145-1156) was used to model specific retention volume data for a series of n-alkane solutes with n-alkane, polystyrene, and poly(dimethylsiloxane) stationary liquid phases. Theoretical equations were derived for the specific retention volume and also for the temperature dependence and limiting (high temperature) values for the specific retention volume. The model was used to predict retention volumes within 10% for the n-alkanes phases; 22% for polystyrene; and from 20 to 70% for PDMS using no adjustable parameters. The temperature derivative (enthalpy) could be calculated within 5% for all of the solutes in nine stationary liquid phases. The limiting value for the specific retention volume at high temperature (entropy controlled state) could be calculated within 10% for all of the systems. The limiting data also provided a new chromatographic method to measure the size parameter, r, for any chromatographic solute using characteristic and size parameters for the stationary phase only. The calculated size parameters of the solutes were consistent, i.e. independent of the stationary phase and agreed within experimental error with the size parameters previously reported from saturated vapor pressure, latent heat of vaporization or density data.