Kazumi Fujimura

OPTICAL RESOLUTION OF SOME MANDELIC DERIVATIVES ON A CHEMICALLY BONDED CYCLODEXTRIN STATIONARY PHASE

Preparation and use of a new type of cyclodextrin-bonded stationary phase are described. Resolution of racemic mandelates and their analogues has been achieved by using this phase. The chiral recognition has been explained in terms of a three-point attachment model. In addition to the inclusion of the aromatic ring of the sample into the cavity of cyclodextrin, enantioselective interaction occurs at two other points; hydrogen bonding of the two polar substituents on the asymmetric carbon atom with secondary hydroxyl groups on the rim of the wider opening face of the cyclodextrin molecule. The effect of the type and position of substituents and other factors responsible for the resolution is discussed.

High-performance liquid chromatographic separation of aromatic carboxylic acids with β-cyclodextrin-bonded stationary phases

Abstract Three β-cycloldextrin-bonded stationary phases, having amino-type spacers of different length, were prepared and their ability to separated isomers of aromatic carboxylic acids based on inclusion complex formation was examined. Two retention mechanisms, inclusion complex formation and anion exchange, were found to determine the elution order of the isomers. An increase in the length of the spacer of bonded cyclodextrin moieties on a silica surface increases the retention and the selectivity by inclusion complex formation.

Studies on ligand-exchange chromatography : V. Gas chromatographic separation of lower aliphatic amines by ligand exchange

In the ligand-exchange gas chromatographic separation of lower aliphatic amines developed, an inorganic cation exchanger (zirconium phosphate) in the Cu2+ form is used as the stationary phase, and the mobile phase is nitrogen gas containing ammonia and water vapour. By studying the effects of the structures of the amines, the cation of the stationary phase and the composition of the mobile phase on the retention values, it has been found that the amine-stationary phase interaction is correlated with the stability of the complexes formed and with steric effects on the amine-metal ion reaction. The concentration of ammonia in the mobile phase also plays an important part in determining retention times and peak resolution.

Salting-out chromatographie separation of hydroxybenzoic acid isomers

Abstract The separation of hydroxybenzoic acid isomers by salting-out chromatography using Amberlite CG-50 (Na+ form) as stationary phase and acidic sodium chloride solution as mobile phase has been studied. The distribution coefficients of hydroxybenzoic acids increased with increase in the concentration of sodium chloride and with decrease in the pH of the solution. The best separation was achieved when a mixture of the o- and m-isomers or the o- and p-isomers was eluted at 40 ± 1° through a column of length 150 mm and I.D. 10 mm with 2 M sodium chloride solution of pH 1.8. The determination of the acids in the eluates by UV spectrophotometry proved that the recovery of the acids was almost quantitative.

Studies on ligand-exchange chromatography : III. Separation of nitrosonaphthol isomers

Abstract The separation of α-nitroso-β- and β-nitroso-α-naphthols by ligand-exchange chromatography was studied. The best results were obtained by use of a strong acid type resin in the Fe 3+ form as a stationary phase and a 50 % v/v ethanolic ammonia solution (pH 9.5 and 12.0) as the mobile phase for stepwise elution. In view of the slow adsorption rate of both isomers to the resin, the Fe(III)-nitrosonaphthol complex formed in the resin phase seems to be a low-spin 1:1 complex for which the oxygen of the hydroxyl group and the nitrogen of the nitroso group are both responsible.

Ligand-exchange high-performance liquid chromatography of aliphatic amines

Abstract The separation and retention behaviour of some aliphatic amines in ligand-exchange liquid chromatography has been studied using copper(II)-modified bonded silica gels as the stationary phase. Hexane containing ammonia and methanol as the mobile phase showed good efficiency for separating sample amines. Ammonia has been found to be very effective for improving both the separation and the peak shape. Sample selectivity and the effect of additives in the mobile phase are discussed.

Studies in ligand-exchange chromatography : Part IV. Separation of hydroxybenzoic and hydroxynaphthoic acid isomers

Abstract The separation of isomers of hydroxybenzoic and hydroxynaphthoic acids by ligand-exchange chromatography using the metallic form of a cation-exchange resin as the stationary phase and dilute aqueous ammonia or water as the mobile phase was studied. The distribution coefficients and the separation factors of hydroxybenzoic acid isomers were larger on the Fe(III) form than on the Ti(IV) form of the resin, but a faster rate of adsorption was observed on the Ti(IV) form rather than on the Fe(III) form of the resin. The separation of hydroxybenzoic acid isomers was best achieved by eluting a mixture of the o - and p -isomers or fo the m - and p -isomers with water through a column of 50 cm in length and 9 mm I.D., packed with the Fe(III) form of the resin which had been equilibrated at pH 4.7 with aqueous ammonia. The controlled surface resin, having sulphonic acid groups only on the surface of the resin beads, was also tested as a stationary phase for the resolution of hydroxynaphthoic acid isomers.

Ligand-exchange gas chromatography of dialkyl sulphides

Abstract The separation and retention behaviour of dialkyl sulphides in ligand-exchange gas chromatography have been studied using a copper(II) stearate stationary phase and an ammonia-containing mobile phase. Short retention times and sharp peaks were obtained when ammonia was introduced into the mobile phase. On a solid copper(II) stearate column a linear relationship was found between the capacity factors and the reciprocal of the ammonia concentration, and some equilibrium constants have been calculated. At higher temperatures, copper(II) stearate behaved as a liquid crystalline stationary phase. A good separation of sulphides was achieved by appropriate adjustment of the ammonia concentration and the column temperature. Factors affecting the retention and sample selectivity are discussed.

Ligand-exchange gas chromatographic separation of aromatic sulphides

Abstract A column packed with copper(I) stearate coated on a diatomaceous support gave a good separation of aryl alkyl sulphide under mild conditions. Good selectivity was also obtained on a column packed with copper(II)-modified Porasil E or F; the use of the latter as a packing material in a capillary column was particularly effective for the separation of positional isomers. Ammonia was effective as a mobile phase ligand, resulting in sharp peaks and suitable retention times. The length and the degree of branching of the alkyl chain of a sample as well as the position of substituents in the benzene ring were found to affect the elution order. The preparation and the use of a Porasil packed column is briefly described.

Ligand-exchange gas chromatographic separation of aniline bases

Abstract Chromosorb G AW DMCS, coated with manganese(II) stearate, was used as column packing in ligand-exchange gas chromatography, and found to be more suitable for the separation of aniline bases than zirconium phosphate microcrystalline gels in the manganese(II) form, because the former has a lower adsorptivity and gives more symmetrical sharp peaks than the latter. From the comparison of retention data of aniline bases obtained on the manganese(II) stearate column with those obtained on the zirconium phosphate column, the retention order was found to be affected not only by the gas-phase basicity and the molecular configuration of the sample compound, but also by the surface structure of the metal support.