Andre Brun

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.

Study of the metabolism of spiramycin in pig liver

A major metabolic pathway of spiramycins in pig liver is described. This biochemical reaction involves L-cysteine--a common amino acid present in most animal tissues--which reacts with the aldehyde function of the antibiotic forming a thiazolidine ring. This transformation of spiramycin derivatives drastically increased their polarity. A preliminary HPLC method enabling the quantitation of each metabolite in the range 0.5 microg/g of liver tissue is proposed. Spiramycin S is used as an internal standard while extraction procedures take into account the physico-chemical properties of the thiazolidine moieties. By comparison, previous HPLC methods underestimated the exact amount of antibiotic residues because these metabolites were not extracted from the studied tissues.

Methodology for transfer of liquid chromatography methods based on statistical considerations

Abstract An important task in the pharmaceutical industry today is analytical transfer. However, no actual guidelines are available today. It is for this reason that we decided to devise a rigorous method using statistic exploitation of results. The statistical technique used is ANOVA (analysis of variance). We chose to treat the case of quantitative analysis in LC but the methodology could easily be adapted to other analytical techniques. The criteria of the transfer validation could be formulated thus: “for each response of interest, the new laboratory must produce results that are not significantly different from those of the reference entity”, or more explicitly by: “the new laboratory must have dispersion characteristics compatible with those of the reference entity and must exhibit no bias”. While compatibility of precision can easily be assessed, the test of absence of bias requires that certified materials be available. Since certified materials can only be obtained through an inter-laboratory study, it means that the reference entity is necessarily a pool of laboratories. Using a single laboratory instead of a pool would not allow a distinction to be drawn between a bias and an inter-laboratory dispersion, which would lead to abnormal transfer failure. The methodology developed was then used on an example. The last part deals with the situation where certified materials are suspected to be slightly degraded. It is explained how such a case, likely to be encountered in pharmaceutical products stored over a long period, can be handled without re-starting the study from scratch.