Jean-Pierre Thomas

Isohydric solvents in liquid-solid column chromatography : Importance for the reproducibility of chromatographic separations and application to the experimental determination of mobile phase polarity

Abstract Isohydric solvents are defined as solvents with water contents corresponding to the same activity of the adsorbent. The influence of the water content of the mobile phase on the activity of the adsorbent and on the reproducibility of separations was studied. A practical means of determining suitable water contents of solvents and solvent mixtures is described. The use of isohydric solvents greatly improves the reproducibility of chromatographic separations. The water contents of isohydric solvents may constitute a scale of relative polarities. In mixtures of isohydric solvents, good linear relationships were obtained between solute capacity factors (k′) and the inverse of the molar fraction of water (1/NH2Oisoh).

Adsorption liquid chromatography on columns : A rational method of mobile phase optimization based on the use of isohydric solvents

Abstract In order to facilitate the use and automation of liquid column chromatography in control laboratories, we have made a classification and a rational combination of solvents. By using an experimental determination of polarity, based on the water content of previously defined isohydric solvents, we have elaborated a method for the optimization of separations that considerably reduces the operating time, gives a more accurate description of processes and greatly limits the number of systems able to solve most of the problems. Practical separations of drug formulations, barbiturates, aromatic bases and phenothiazines are considered.

Spherosil for high-performance, moderate-pressure liquid chromatography

Abstract The aim of this study was to prove experimentally that an inexpensive high-performance liquid chromatography system for routine control, operating at moderate pressures as predicted by the theoretical optimization model of Martin, Eon and Guiochon, is feasible. Two improved types of Spherosil, XOA 600 and XOA 800, lead to better selectivities and efficiencies (800 plates/cm), short columns (5–10 cm), that can be operated at moderate pressures (10–30 bar) and reasonable analysis times (5–15 min). The low pressure drops are due mainly to: the spherical shape of the particles, an average particle diameter of 5–7 μm, a narrow particle-size distribution (90% of the fraction between the limits d p ± 2 μm), a high specific surface area (600 or 800 m 2 /g) (the larger the surface area the shorter is the column and consequently the lower the pressure drop) and the linear velocity of the mobile phase fixed at the minimum of the Van Deemter curve. Numerous examples of separations confirm the potential of this new trend in high-performance liquid chromatography.