G. Bicker

Enantiomeric separation of dansyl amino acids using MECC with a ligand exchange mechanism

Enantiomeric separation of 11 dansyl amino acids is reported using micellar electrokinetic capillary chromatography. The chiral phase consisted of a copper complex of N, N-di-decyl-D-alanine dissolved in the running buffer. Several factors affecting the separation were studied. The partitioning of the copper complex between the micelles and the buffer interface was investigated, and an attempt to describe the mechanism of separation is presented.

Determination of stoichiometric coefficients and apparent formation constants for α- and β-CD complexes of terpenes using reversed-phase liquid chromatography

Abstract The stoichiometric coefficients and apparent formation constants for (±)- α -pinene, (±)- β -pinene, (±)-camphene and (±)-limonene with α- and β-cyclodextrins were determined using high-performance liquid chromatography. These measurements were performed in 55:45 0.1% orthophosphoric acid in water-methanol using a Vydac C 4 column (15.0×0.46 cm I.D., 10 μm, 300A). Using α-cyclodetrin (α-CD), 1:2 guest-CD complexes were found for the three bicyclic compounds, α- and β-pinene and camphene; a 1:1 guest-CD complex was found for limonene. Using β-cyclodextrin (β-CD), 1:1 guest-CD complexes were found for all compounds. Recognition of the terpene enantiomers was only achieved for the bicyclic compounds using α-CD. For α- and β-CD, the apparent formation constant for each terpene-CD complex was calculated.

Separation of Organophosphonates by Ion Chromatography with Indirect Photometric Detection

Abstract An ion chromatographic method which utilizes lithium trimesate to separate three diphosphonate drugs and two process related organophosphonates is described. The lack of a chromophore on the five species and the high absorptivity of the trimesate anion at 254 nm allows for facile detection using indirect photometry. The effects of mobile phase concentration on the capacity factor of the species were investigated and a logarithmic relationship was established which was found to be dependent on the charge of the analyte anion and the mobile phase anion.

Use of subcritical fluid chromatography for the separation of enantiomers using packed cellulose based stationary phase

Investigations into the parameters affecting the enantiomeric separation of an intermediate in the synthesis of a drug targeted for cardiac arrhythmia is presented. The separation was achieved under subcritical fluid chromatography using CO2 modified with methanol and co-modifiers isopropyl amine and methylene chloride. The stationary phase was a cellulose based stationary phase manufactured under the trade name Chiracel OB. The results showed the addition of methylene chloride had a noticeable effect on resolution while the separation factor, α, remained constant. The co-modifier, isopropyl amine, did not considerably influence the resolution, or separation factor. Temperature studies were performed in order to establish the thermodynamic parameters of the interaction between the enantiomers and the stationary phase. Plots of In k′ vs. 1/T proved to be curved, while plots of In α vs. 1/T were linear.

Enantiomeric separation of enzymatic hydrolysis products of dihydropyrimidinone methyl ester with cationic cyclodextrin by capillary electrophoresis.

The achiral separation of dihydropyrimidinone (DHP) methyl ester and its corresponding carboxylic acid and the chiral separation of their respective enantiomers were achieved in a single analysis using capillary electrophoresis (CE) with quaternary ammonium-beta-cyclodextrin (QA-beta-CD) as a chiral buffer additive. Separation of the DHP methyl ester from the corresponding carboxylic acid was achieved because the acid was negatively charged at pH 8.3 of the running buffer and the ester is neutral. Upon the addition of QA-beta-CD, the enantiomers of the acid and ester were well resolved before and after the electroosmotic flow, respectively. In addition, the minor DHP methyl ester enantiomer (R isomer) was well separated from several impurities. This CE system was used to monitor the progress of a bioresolution reaction that utilizes an enzyme to convert the R isomer of the ester to its corresponding acid. The quantities of all four enantiomers can be determined using a single set of CE conditions. In addition, it is demonstrated that samples can be directly injected into the capillary without sample pretreatment due to the fact that the coating of the cationic CD on the capillary surface prevents adsorption of the positively charged enzyme. The effects of other experimental parameters such as type of CDs, concentration of CDs, pH, temperature, and the preconditioning of capillary were also studied.

Electrophoretic chiral separation of pharmaceutical compounds with multiple stereogenic centers in charged cyclodextrin media

This paper reports the use of sulfated β-cyclodextrins (S-β-CDs) (degree of substitution (DS) = 7-11 and 15), hepta-6-sulfato-β-CD (HS-β-CD), heptakis (2,3-dimethyl-6-sulfato)-β-CD (HDMS-β-CD), and heptakis (2,3-diacetyl-6-sulfato)-β-CD (HDAS-β-CD) in conjunction with capillary zone electrophoresis (CZE) to separate enantiomers of several commercially available pharmaceutical compounds with multiple stereogenic centers. Compounds studied include eucatropine, fenoterol, nadolol, nafronyl, nylidrin, and pentapiperide. S-β-CD with a relatively high degree of substitution is shown to be effective in separating several of these compounds due to the high selectivity. Resolution of four isomers was achieved for several of the test compounds under counter-electroosmotic flow (EOF) conditions in less than ten minutes. Data illustrating the effects of CD concentration and pH are presented. It is also shown that the migration order of isomers can be manipulated by changing either the CD concentration or buffer pH.

The Quantitation of a Residual Quaternary Amine in Bulk Drug and Process Streams Using Capillary Electrophoresis

Abstract A capillary electrophoretic method for the determination of a residual alkyl quaternary amine, tetra-n-butylammonium ion (TBA+), in bulk drug and process streams was developed. Since the analyte does not have a chromophore, detection was performed utilizing indirect photometric detection. The influence of the quinine, tetrahydrofuran and sodium acetate concentrations and pH app in the background electrolyte solution upon the efficiency of the separation and effective electrophoretic mobility of both TBA+ and electro-osmotic flow were studied. The ranges in which the various parameters were examined had considerable effects upon both the efficiency and the effective electrophoretic mobility of the electro-osmotic flow; however, the effective electrophoretic mobility of TBA+ was not significantly affected. The optimized method was validated in terms of detector linearity, sensitivity, precision and accuracy.

Chromatographic Analysis of Residual Acetate in Bulk Drugs

Abstract An ion chromatographic method for the determination of the residual acetate in hulk drug was developed. The drug was MK0476, an LTD4 antagonist. The compound also has a carboxyl functionality, which would interfere with the detection of the acetate ion. A solid phase extraction through a Sep-Pak cartridge was pursued for the removal of MK0476 from the matrix. Since the analyte does not have a chromophore, a mobile phase containing trimesic acid facilitated its detection by indirect photometric detection. The separation was performed on a polymeric strong union exchange column. The influence of pH, concentration of trimesic acid, and temperature were studied. Chloride ion was found to be a contaminant that was interfering in the analysis. To improve the separation between chloride and acetate ions, methanol was added to the mobile phase, leading to complete separation between the two species. Recovery of the acetate ion was determined as 92.3%. The method was applied to real samples with good resu...

Determination of bis(tributyltin) oxide by GC–MS with on-line hydride derivatization: application to drug substance analysis

We report the determination of residual bis(tributyltin) oxide in a drug substance by GC-MS after extraction and on-line conversion to tributyltin hydride. Gas chromatography was performed using a 15 m x 0.25 mm i.d. DB-5 HT column with a temperature program from 100 to 160 degrees C at 15 degrees C min(-1). A mass range of 165-185 amu was monitored with the MS detector. Hydride generation is performed by placing a small amount of solid sodium borohydride in the injection port of a gas chromatograph and injecting samples and standards through this material. Conversion to tributyltin hydride is shown to be quantitative and linear for levels of bis(tributyltin) oxide between 1 and 100 ppm in the drug substance. The use of GC-MS provides sensitive and selective detection of tin containing species and the tin isotope pattern allows for confirmation of the presence of tin in chromatographic peaks. Recovery at 6 ppm was 89% with an injection precision of 6%. The limit of detection for bis(tributyltin) oxide in drug substance is 1 ppm.

Flow injection determination of Triton X-100 with on-line solid-phase extraction

A simple and rapid method for the determination of Triton X-100 in the presence of a quinoline derivative is described. The method involves flow injection with on-line cation-exchange solid-phase extraction. The carrier consists of a mixture of 5 mmol dm–3 aqueous KH2PO4(pH 2.0) and isobutyl alcohol–acetonitrile (50 + 50, v/v) in the proportion 65 + 35, v/v. Under these conditions, Triton X-100 elutes unretained, while the quinoline derivatives are retained on the extractor. Authentic samples were analysed by this method, with good precision and reproducibility.