Lucas Fotsing

Determination of six water-soluble vitamins in a pharmaceutical formulation by capillary electrophoresis.

A method was developed for the quantitative analysis of six water-soluble vitamins (thiamine, nicotinamide, riboflavine, pyridoxine, ascorbic acid and pantothenic acid) in a pharmaceutical formulation, using free solution capillary zone electrophoresis (CZE) in uncoated fused silica capillaries and UV detection. The influence of different parameters, such as the nature of the buffer anionic component and buffer concentration on the CZE separation of vitamins was investigated using four vitamins of the B group as model compounds. A good compromise between resolution, analysis time and analyte stability was obtained by use of a 50 mM borax buffer of pH 8.5. This CZE method was found to be very useful for the separation of more complex samples, a mixture of ten water-soluble vitamins being completely resolved in about 10 min. However, cyanocobalamine could not be separated from nicotinamide in this CZE system, the two compounds being in uncharged form at the pH used. These two compounds could easily be resolved by micellar electrokinetic chromatography (MEKC), the anionic surfactant dodecylsulfate being added to the running buffer at 25 mM concentration. In the pharmaceutical formulation, some excipients were found to be adsorbed to the capillary surface, giving rise to a progressive decrease of the electroosmotic flow and consequently to a simultaneous increase of analyte migration times. A capillary wash with sodium hydroxide had to be made between successive runs in order to minimize these effects. Good results with respect to linearity, precision and accuracy were obtained in the concentration range studied for the six vitamins, using nicotinic acid as internal standard.

Enantioseparation of uncharged compounds by capillary electrophoresis using mixtures of anionic and neutral β-cyclodextrin derivatives

Abstract The use of the polyanionic sulfobutyl-β-cyclodextrin in combination with a neutral cyclodextrin derivative such as trimethyl-β-cyclodextrin (TMCD) or dimethyl-β-cyclodextrin (DMCD) in a pH 3 phosphoric acid–triethanolamine buffer has proved to be very suited to the enantioseparation of acidic compounds such as non-steroidal anti-inflammatory drugs. In this paper, the usefulness of such dual cyclodextrin systems was evaluated for the enantioseparation of weakly acidic and neutral compounds. Fairly good results with respect to chiral resolution were obtained at pH 3 for weak acids in these dual systems. However, no complete enantioseparation could be achieved under these conditions for the neutral drug chlormezanone. Another ionizable derivative, carboxymethyl-β-cyclodextrin, was then investigated together with TMCD or DMCD at pH 3 and 5. After optimisation of the concentration of the neutral cyclodextrin derivative, high enantioresolution could be obtained at pH 5 for chlormezanone as well as for all the other compounds tested.

Stereoselective determination of S-naproxen in tablets by capillary electrophoresis.

A capillary electrophoresis (CE) method was developed for the stereoselective determination of the non-steroidal anti-inflammatory drug (NSAID), S-naproxen, in tablets. Several beta-cyclodextrin derivatives (CDs) were tested as chiral selectors, including sulfobutyl-beta-CD (SBCD), carboxymethyl-beta-CD (CMCD), dimethyl-beta-CD (DMCD) and trimethyl-beta-CD (TMCD), in a phosphoric acid/triethanolamine pH 3 buffer. Under these conditions, the analyte was mainly present in an uncharged form and therefore, the use a neutral CD (DMCD or TMCD) alone could not lead to enantiomeric separation. On the contrary, by addition of a charged CD (SBCD or CMCD) to the running buffer, giving the analyte enantiomers an adequate mobility, chiral resolution could be achieved, although the resolution values obtained in this case were not quite satisfactory (Rs < 1.5). Dual systems, based on the use of mixtures of charged and neutral CDs, were then investigated. The SBCD/TMCD system was found to be particularly well suited to the enantioseparation of naproxen and after optimisation of the concentrations of both CDs, a resolution value of 5.4 could be obtained. The method was validated for the determination of R-naproxen (enantiomeric impurity) in the 0.1-2% range, using the racemic mixture of the analyte. A second validation was performed in the 50-150% range for the quantitation of S-naproxen. In both cases, good results with respect to linearity, precision and accuracy were obtained.

Elimination of adsorption effects in the analysis of water-soluble vitamins in pharmaceutical formulations by capillary electrophoresis

A tendency to an increase in migration times was observed when different water-soluble vitamins were analysed repeatedly in pharmaceutical preparations by capillary electrophoresis. In order to better understand the origin of this effect, the influence of the vitamins and the excipients, such as cellulose derivatives, was investigated. These studies indicated that the increase in analyte migration times was most probably due to the adsorption of different kinds of constituents to the capillary wall. Different rinsing procedures were tested in order to eliminate these unfavourable effects. A rinse of the capillary with a 25 mM sodium dodecyl sulfate (SDS) solution in the running buffer between successive runs was found to be particularly effective when the analysis was performed by free solution capillary zone electrophoresis (CZE). When the vitamins were determined by micellar electrokinetic chromatography (MEKC) using SDS as surfactant, a short capillary rinse with the running buffer was sufficient to obtain reproducible migration times. The CZE and MEKC methods developed were validated and compared. Both methods could be applied to the determination of water-soluble vitamins in different multivitamin formulations.

Liquid chromatographic analysis of local anesthetics in human plasma after sample preparation by on-line dialysis. Optimization by use of experimental design

SummaryA fully automated method involving dialysis, clean-up and enrichment of the dialysate on a pre-column packed with a strong cation-exchange phase, and subsequent liquid chromatographic (LC) analysis with UV detection at 220 nm has been developed for the determination of local anesthetics (prilocaine, mepivacaine, and bupivacaine) in human plasma. All sample-handling operations were executed automatically by means of an Asted XL system.To identify the most important conditions affecting analyte recovery from the dialysis and trace-enrichment processes, a seven-factor D-optimal design with 16 experimental points was elaborated as a screening test. A four-factor D-optimal design with 24 experimental points was then used to predict and optimize analyte recovery. Derringers desirability function was also used to deduce optimum conditions for analyte recovery and dialysis time within the experimental domain.Finally, the method developed was validated. Mean recoveries were approximately 72% for bupivacaine and approximately 67% for mepivacaine and prilocaine. The limits of quantification were 28 ng mL−1 for bupivacaine and 25 ng mL−1 for mepivacaine and prilocaine.

Multivariate optimization approach for the separation of water-soluble vitamins and related compounds by capillary electrophoresis.

Due to its high separation efficiency and its different selectivity, capillary electrophoresis (CE) has proved to be useful as a complementary technique to liquid chromatography for the determination of drug-related impurities. In contrast to the univariate approach (i.e. a systematic variation of a single parameter while maintaining the other factors constant), experimental designs involve a simultaneous alteration of all variables according to a predefined matrix of experiments. The multivariate approach allows optimum conditions to be obtained with a minimum number of experiments. In order to determine simultaneously by CE a series of water-soluble vitamins, such as thiamine, riboflavin, nicotinamide, adenine, pantothenic acid, pyridoxine, ascorbic acid, biotin, rutin andp-aminobenzoic acid, and some related compounds, such as lumiflavine, nicotinic acid, pyridoxamine and thiamine monophosphate, experimental designs have been applied.