F. P. B. Van Der Maeden

Oligomer separations by gradient elution high-performance liquid chromatography

Summary Gradient elution high-performance liquid chromatography (HPLC) on chemically modified silica is very suitable for both the qualitative and quantitative analysis of oligomeric mixture, as has been demonstrated for low-molecular-weight resins, pre-polymers and extracts obtained from high polymers and in studying the kinetics of the early stages of polymerization and polycondensation reactions. Examples are given of oligomer separations with epoxy resins, novolak resins, poly-(2,6-diphenyl- p -phenylene oxide). (Tenax), poly(ethylene terephthalate) and poly(ethylene oxide) derivatives. All of these separations easily permit quantification, as has been demonstrated for ethoxylated octylphenol, provided that strict standardization is maintained throughout the analysis. Coefficients of variation of the peak-area measurements of the 19 oligomers observed in this sample were low (1–4%); the coefficients of variation of the retention times ranged from 0.01 to 0.3%. Using commercially available chemically modified column packing materials, the resolution in the gradient elution HPLC of oligomers is adversely affected by size exclusion and sample solubility.

Quantitative analysis of d-tubocurarine chloride in curare by column liquid chromatography.

An improved quantitative analysis of d-tubocurarine chloride in the plant extract curare is presented. Gradient high-performance liquid chromatography on a hydrophobic stationary phase was found to be very suitable for the analysis of quaternary ammonium bases such as the complex mixture of curare alkaloids. Owing to the residual free silanol groups on the modified silica surface, the curare alkaloids are eluted from a reversed-phase column only if an electrolyte is added to the mobile phase. In order to optimize the separation, the effects of pH, the nature of the cation in the buffer and the concentration of the buffer of the retention of the alkaloids were investigated. Using a tetramethylammonium phosphate buffer at pH 4 in a gradient of water-methanol, undesirable retardation effects on the reversed-phase column could be suppressed sufficiently. As a result, an accurate method for the determination of d-tubocurarine chloride in curare was obtained. The coefficient of variation of this analysis is only 1.3%.

Gel permeation chromatography on unmodified silica using aqueous solvents

Summary Chemically unmodified, totally porous, spherical silica particles ( e.g. , LiChrospher from Merck, Darmstadt, G.F.R.) were found to be very suitable for the rapid gel permeation (size-exclusion) chromatography of water-soluble polymers. These materials permit the easy preparation of high efficiency columns. With 10-μm LiChrospher particles, plate numbers > 30,000 per metre were obtained for glucose as a totally permeating solute and water as the mobile phase on 30 × 0.46 cm columns at a flow-rate of 0.5 ml/min. The apparent molecular weight of polyelectrolytes depends on the concentration of the polyelectrolyte and the ionic strength of the mobile phase because of polyelectrolyte expansion and ion-exclusion effects. Adsorption on the silica surface of non-ionic and cationic polymers can be prevented by using a tetramethylammonium salt as a physical modifier.

High-performance liquid chromatography of proteins on alumina

Abstract Proteins can be separated on alumina with an aqueous mobile phase by ion-exchange and size exclusion chromatography and by a combination of both techniques. The pH dependence of the ion-exchange retention mechanism is explained on the basis of two similar concepts: the isoelectric point of the protein and the zero point of charge of the alumina surface. The possibility of infuencing the surface properties of alumina by the choice of the buffer anion lends great flexibility to the system. However, the size exclusion selectivity is limited owing to the small choice of presently available aluminas. Examples are given that demonstrate the advantages of alumina for the separation of strongly basic proteins at high pH.

Derivatization of some polymers with o-phthalaldehyde prior to high-performance size-exclusion chromatography

Abstract The well known OPA ( o -phthalaldehyde) derivatization commonly used in aqueous media has been modified on order to be able to carry out the reaction with various polymeric materials in tetrahydrofuran, a solvent very often used in size-exclusion chromatography. The modified OPA reaction leads to stable fluorescent derivatives of the investigated analytes. The derivatization procedure has three important advantages: (i) the selectivity of the analytical method is greatly improved since only compounds having a primary amino group are detected; (ii) the sensitivity is increased by at least two orders of magnitude compared to ultraviolet or refractive index detection; (iii) the chromatography is facilitated due to a conversion of the primary amino groups.