Gilbert Blu

The use of syringe-type pumps in liquid chromatography in order to achieve a constant flow-rate

Abstract The variation of the flow-rate of mobile phase pumped through a chromatographic column by a screw-driven syringe-type pump is discussed. It is shown that because of the compressibility of liquids, a steady-state flow is achieved only after a long period, which depends on the characteristics of the pump, the flow resistance of the column and the nature of the liquid. This period is normally between 15 and 60 min if liquid pumping starts from zero pressure at a constant piston speed. The retention times observed for compounds injected during the transitory period can be up to several times greater than those observed for the same compounds under steady-state conditions. All retention data and efficiencies measured during the transitory period are not reproducible and are meaningless. Quantitative results also are not reproducible. Instructions are given for the better use of this type of pump, which, in spite of some well-known advantages, has been found to be very difficult to use for any measurements.

Derivation of the differential heat of dissolution or adsorption from gas-liquid chromatographic measurements

Taking into account the non-ideality of the gas phase, this paper develops a theory for the determination of the differential heat of dissolution, ΔHS, from gas-liquid chromatography measurements. When ΔHS is determined over a small interval of temperature, the calculation of ΔHS can be made from measurements of retention times only without using the retention volumes. Using a carefully designed equipment, and accuracy in ΔHS of better than 1% could be reached when ΔHS is measured over an interval of temperature of one degree.

Détermination de la chaleur différentielle d'adsorption par chromatographie gas-solide

Abstract Using various results of thermodynamic theories on gas-solid adsorption, the equations giving the retention times of solutes in gas-solid chromatography are established for the case where the gas phase is not ideal. The method for the determination of heats of adsorption already described for gas-liquid chromatography cases, with these data, can be extended to gas-solid chromatography: with carefully designed equipment an accuracy of about 1% can be reached in the determination of differential heat of adsorption.