Shigeru Terabe

Electrokinetic chromatography: an interface between electrophoresis and chromatography

Abstract Electrokinetic chromatography is a new type of analytical separation method, which utilizes the experimental technique of capillary zone electrophoresis in combination with the principle of chromatography. A theoretical plate number of 250 000 is easily obtained in 10 min.

chiral separation by electronkinetic chromatography while bile salt micelles

Abstract Various bile salt solutions were employed for micellar electrokinetic chromatography. Many racemic dansylated amino acids were successfully resolved, especially with a taurodeoxycholate solution under acidic conditions. Apparent capacity factors and apparent separation factors of racemic Dns-amino acids were determined from retention times of the solute, the micelle and methanol. Retention parameters of charged solutes and the effect of electroosmosis on resolution are discussed and a possible chiral separation mechanism is suggested.

Electrokinetic chromatography with 2-O-carboxymethyl-β-cyclodextrin as a moving “stationary” phase

Abstract Preliminary results are presented on a new type of liquid chromatography, based on inclusion complex formation in a solution of a β-cyclodextrin derivative having an ionized group, 2-O-carboxymethyl-β-cyclodextrin (β-CMCD), combined with electrokinetic migrations. Only the host—guest interaction between β-CMCD and the solute operates as the distribution process, and electroosmosis and electrophoresis in an open-tubular capillary filled with a β-CMCD solution permit differential migrations between the host and guest molecules. Separations of some aromatic isomers are shown, and retention parameters and the distribution coefficient are discussed.

Electrokinetic chromatography with micellar solutions : Separation of phenylthiohydantoin-amino acids

Abstract A mixture of 22 phenylthiohydantoin-amino acids was separated by electrokinetic chromatography with a sodium dodecyl sulphate (SDS) solution and a 650 × 0.05 mm I.D. fused-silica tube. This chromatography is based on micellar solubilization and electrokinetic migration in an open-tubular capillary. The retention times of the solutes could be controlled by changing the SDS concentration, the applied voltage or the length of the separation tube. Dodecyltrimethylammonium bromide (DTAB) solutions were also employed. The separation characteristics with SDS solutions were completely different from those with DTAB solutions. The resolutions were better with the former than with the latter solution, but for some solutes the latter gave better results.

Electrokinetic chromatography with micellar solutions : Retention behaviour and separation of chlorinated phenols

The retention behaviour of chlorinated phenols during electrokinetic chromatography with micellar solutions and open-tube capillary columns was investigated. The capacity factor for each compound of a test mixture was calculated by considering both the effects of micellar solubilization and electrophoresis of the ionized solute, even when a solute was ionized. Under conditions where a solute, a chlorinated phenol, was estimated to be partially ionized, the capacity factor of the solute decreased with an increase of pH, whereas that of an electrically neutral solute was almost constant regardless of the change in pH. All the isomers of chlorinated phenols were completely separated within 18 min by using a 650 × 0.05 mm I.D. fused-silica tube with a 0.07 M sodium dodecyl sulphate solution (pH 7.0).

Enantiomeric resolution by micellar electrokinetic chromatography with chiral surfactants

Abstract Enantiomeric resolution of phenylthiohydantoin (PTH)-amino acids by micellar electrokinetic chromatography using chiral surfactants was studied. As a chiral surfactant, digitonin, which is a non-ionic compound, was used with anionic sodium dodecyl sulphate (SDS) to form mixed micelles. Under acidic conditions (pH 3.0), PTH derivatives of six amino acids (tryptophane, norleucine, norvaline, valine, α-aminobutyric acid and alanine) were separated from each other and optically resolved with a 25 m M digitonin-50 m M SDS solution, although a long separation time was required. The use of an anionic chiral surfactant, sodium N-dodecanoyl- l -valinate, was also examined under neutral conditions. In this instance, the same enantiomers as above except PTH- dl -Ala were resolved in a shorter time.

Separation and determination of lipophilic corticosteroids and benzothiazepin analogues by micellar electrokinetic chromatography using bile salts.

The separation of corticosteroids and benzothiazepin analogues by micellar electrokinetic chromatography (micellar EKC) was studied in comparison with capillary zone electrophoresis. The separation of these substances was not successful under neutral and alkaline conditions because they migrated with the same velocity as that of the electroosmotic flow. Micellar EKC with sodium dodecyl sulphate (SDS) solutions was also not successful because these substances migrated with almost the same velocity as that of the SDS micelle, owing to their high lipophilicity. The use of bile salts, which have a similar skeleton to corticosteroids, as the micellar phase permitted the separation of these substances with high theoretical plate numbers (150,000-350,000) within a short time (ca. 15 min). Sodium cholate was particularly useful. The effects of bile salt concentration, pH and the addition of methanol were investigated. Micellar EKC was also applied to the determination of the drug substances in tablets and cream using the internal standard method and to purity testing of drug substances and tablets.

Separation of water-soluble vitamins by micellar electrokinetic chromatography

The retention behaviour of eleven water-soluble vitamins in micellar electrokinetic chromatography (micellar EKC) was investigated in comparison with capillary zone electrophoresis. Sodium dodecyl sulphate (SDS) and sodium lauroylmethyl taurate were used as the anionic surfactants at concentrations of 0.05-0.2 M in micellar EKC. The retention times of cationic substances increased more rapidly with increasing concentration of the anionic surfactant than those of other substances. This result suggests that ion-pair formation between cationic substances and anionic surfactants contributes to the retention of the former. The difference in the structures of the two surfactants affects the retention behaviour of solutes, especially cationic substances. To clarify the effect of the micelle, an ion-pairing agent that does not form the micelle structure was employed. All solutes were successfully separated within 15 min by using a 650 mm x 0.05 mm I.D. fused-silica tube with a 0.05 M SDS solution (pH 9.0) to give theoretical plates ranging from 100,000 to 350,000.

Separation of β-lactam antibiotics by micellar electrokinetic chromatography

Abstract The retention behaviour of β-lactam antibiotics in micellar electrokinetic chromatography (EKC) was investigated. Sodium dodecyl sulphate (SDS) and sodium N-lauroyl-N-methyltaurate were used as anionic surfactants at concentrations of 0.05–0.3 M. It was found that the retention of ionic substances in micellar EKC is determined by the following three factors: the electrophoretic migration of the ionic substances, the interaction between the ionic substances and ionic surfactants and solubilization of the solute by the micellar phase. A difference in the retention behaviours of cationic substances was observed between the two anionic surfactants, which have different groups neighbouring the charge-bearing groups. The effect of an ion-pairing reagent was also investigated to make the effect of the micelle clearer. All test solutes were successfully separated by micellar EKC at SDS concentrations above 0.1 M, with theoretical plate numbers ranging from 70 000 to 260 000.

Chiral separation of trimetoquinol hydrochloride and related compounds by micellar electrokinetic chromatography using sodium taurodeoxycholate solutions and application to optical purity determination

Abstract The chiral separation of trimetoquinol hydrochloride, which is a bronchodilator (Inolin), and three related compounds by micellar electrokinetic chromatography was investigated using a bile salt as a chiral surfactant. Enantiomers of these compounds, except laudanosoline, were successfully separated within 12 min using a separation tube of effective length 500 mm × 0.05 rum i.d. and a 0.05 M sodium taurodeoxycholate solution of pH 7.0. The observed theoretical plate numbers of the peaks were ca. 150000. Chiral recognition was affected by the structure of bile salts, the pH of the buffer solutions used and the structure of the solutes. Of four kinds of bile salts, successful chiral separation was achieved only using sodium taurodeoxycholate solution under neutral conditions. The method was applied to the optical purity determination of trimetoquinol hydrochloride. The effects of surfactant concentrations and some additives to the micellar solution are briefly described.