M.R. Detaevernier

Use of capillary electrophoresis for the determination of vitamins of the B group in pharmaceutical preparations

Abstract The separation of four water-soluble vitamins, i.e ., thiamine, riboflavine, pyridoxine and nicotinamide, was investigated by capillary zone electrophoresis and micellar electrokinetic chromatography. The usefulness of the internal standard technique in order to improve the precision of peak area when either the migration time or the injection volume varied was demonstrated. Quantitative analyses of different pharmaceutical formulations were compared with the LC method of the US Pharmacopeia. A good correlation was obtained.

Preparation of β-artemether liposomes, their HPLC–UV evaluation and relevance for clearing recrudescent parasitaemia in Plasmodium chabaudi malaria-infected mice

Egg phosphatidylcholine-cholesterol liposome formulations containing the antimalarial drug beta-artemether have been prepared and analyzed for their encapsulating capacity, chemical stability, leakage, in vitro release and their therapeutic efficiency against Plasmodium chabaudi infection. A HPLC-UV analysis of beta-artemether liposomes without derivatisation was achieved. A good linearity of y=4437.7 x+469.01 (R(2)=0.9999) with a detection limit of 2 microg ml(-1) was reached. Prior to this, liposomal formulations composed of different molar ratios of EPC-CHOL were prepared to select beta-artemether crystal-free liposome preparations. The formulation corresponding to 4:3 and a total concentration of 300 mg lipids ml(-1) buffer (pH 7.2), which could incorporate as much as 1.5 mg beta-artemether was selected for therapy. A trapping efficiency of nearly 100% was reached, the drug being located in the lipid bilayers. A dialysis test demonstrated that the drug could be reversibly released from the liposomes, reaching equilibrium within 24 h. After 3 months storage at 4 degrees C, no leakage of beta-artemether had occurred indicating a high stability of the liposomes. These liposomes were used to treat mice infected with the virulent rodent malaria parasite Plasmodium chabaudi chabaudi, with a 100% cure by clearing the recrudescent parasitaemia.

Determination of the enantiomeric purity of dexfenfluramine by capillary electrophoresis: use of a Plackett—Burman design for the optimization of the separation

Abstract For the investigation of the stereochemical purity of the anorectic drug dexfenfluramine, a capillary electrophoretic method is presented using the chiral selector dimethyl β-cyclodextrin (DMCD). A Plackett—Burman experimental design was used as a multivariate strategy for the evaluation of the effects of varying several operating conditions at once. The impact of concentration of DMCD, concentration of methanol added to the buffer, pH of the background electrolytes, temperature of the capillary and applied voltage, has been investigated on the resolution of the enantiomers, the analysis time and the peak symmetry. From these results, optimal values of the variables were selected for the development of a method capable of determining the levo-rotatory enantiomeric impurity of dexfenfluramine.

The determination of platinum in biological fluid by means of graphite furnace atomic absorption spectrometry

Methods are described for the determination of aluminium in serum and in diluted urine by means of graphite furnace atomic absorption spectrometry. For the analysis of serum, thermal decomposition of the sample in the furnace, using a ramp charring program, was found to be necessary in order to eliminate the organic material. The precision of the method was 10%. For urine the relative deviation was 9%. The precision was markedly improved by the use of an automatic sample injector (5.3%). Since large contamination problems make the determination of Al at the parts per billion (ppb) level very difficult, special attention was paid to the precautions to be taken in order to avoid external aluminum contamination.

Separation and simultaneous determination of the components in an analgesic tablet formulation by micellar electrokinetic chromatography

Abstract The separation and simultaneous determination of the active ingredients of an analgesic tablet formulation composed of caffeine, paracetamol, dextropropoxyphene, acetylsalicylic acid and chlorpheniramine was investigated by micellar electrokinetic chromatography (MEKC). As the use of sodium dodecyl sulphate could not resolve the two basic compounds, the separation was completed by using a mixture of the bile salts sodium cholate and sodium deoxycholate. The determination of the five ingredients together with salicyclic acid could be performed with acceptable accuracy and precision.

Simultaneous determination of ketoconazole and formaldehyde in a shampoo: liquid chromatography method development and validation

Ketoconazole is an antifungal agent, which is the active ingredient in a shampoo primarily used for the treatment of seborrhatic dermatitis (anti-dandruff shampoo). The shampoo also contains imidazolidinylurea as a formaldehyde releasing preservative. The aim of this study was to develop a HPLC system that allows the determination of both ketoconazole and formaldehyde. The finally selected isocratic system consisted of an Interchrom Nucleosil (250 X 4.6 mm, 5 microm) C8 column and a mobile phase containing acetonitrile-phosphate buffer 0.025 M, pH 4.0, 45/55 (v/v). Ketoconazole could immediately be determined at 250 nm after injection of diluted shampoo. Formaldehyde was measured at 345 nm after derivatisation with a 2,4-dinitrophenylhydrazine solution. At the selected conditions, the other excipients of the shampoo did not interfere in the assays for both substances. Method validation was performed on both assays. Different selectivity towards ketoconazole and formaldehyde was observed when applying other C8 columns. This fact, however, did not affect the assays of both substances.

Development of a validated capillary electrophoresis method for enantiomeric purity testing of dexchlorpheniramine maleate

A capillary zone electrophoresis method has been developed for the detection of 0.1% of (R)-levochlorpheniramine maleate in samples of (S)-dexchlorpheniramine maleate. Using 1.5 mM carboxymethyl-beta-cyclodextrin in an acidic background electrolyte, resolution values of more than 10 were obtained. Under these conditions the R-enantiomer is migrating in front of the bulk S-enantiomer. The assay was validated for linearity (2-10 microg/ml; R2 = 0.9992), selectivity [(RS)-pheniramine maleate and (RS)-brompheniramine maleate], limit of detection (0.25 microg/ml), limit of quantification (0.75 microg/ml), analytical precision (intra- and inter-day variability), repeatability of the method (RSD = 5.0%) and accuracy. In samples of dexchlorpheniramine maleate from two different manufacturers, concentrations of, respectively, 0.15% and 1.95% (m/m) of levochlorpheniramine maleate were detected. The method was compared to the HPLC method described in the European Pharmacopoeia III monograph.

Development of a standardized analysis strategy for basic drugs, using ion-pair extraction and high-performance liquid chromatography — II. Selection of preferred HPLC-systems

A test set of 100 basic drugs has been chromatographed on 16 preselected HPLC-systems using four different types of stationary phase (Si-, NH2-, CN- and C18-). A numerical treatment of the chromatographic data, based on the discriminating power concept, results in the selection of two preferred HPLC systems for basic drugs. both using the CN-bonded phase. The preferred eluents are n-heptane-dichloromethane-acetonitrile-propylamine (25:50:25:0.1) and acetonitrile-water-propylamine (90:10: 0.01). The two preferred HPLC systems are adopted in a standardized analysis strategy.

Suppression of chiral recognition of 3-hydroxy-1,4-benzodiazepines during micellar electrokinetic capillary chromatography with bile salts

During the development of a micellar electrokinetic chromatographic screening method for 1,4-benzodiazepines, peak splitting and broadening were observed for some 3-hydroxy-1,4-benzodiazepines (oxazepam, lorazepam, temazepam and lormetazepam). This phenomenon occurred when the micellar phase consisted of bile salts and can be ascribed to the chiral nature of these surfactants. As the bile salts were applied in order to reduce the capacity factors to an appropriate level, enantiomer separation was not an objective and even disturbing. By increasing the analysis temperature, the chiral recognition of these compounds could be suppressed.

Development and evaluation of a linear regression method for the prediction of maximal chiral separation of basic drug racemates by cyclodextrin-mediated capillary zone electrophoresis

An important step in method development of chiral separations with neutral cyclodextrins (CDs) as chiral selectors is the estimation of the CD concentration that gives the highest degree of separation. From the equation [S]opt=1/(K1K2)(1/2) this optimal CD concentration can be calculated if any knowledge is available about the binding constants K1 and K2 of both enantiomer complexes. These values can be obtained by measuring the effective velocities of each enantiomer as a function of the selector concentration and fitting these profiles by non-linear least-square regression. An alternative approach has been developed which makes it possible to predict the optimal CD concentration from a few experiments performed at low CD concentrations. The model is developed using some antimycotic imidazole derivatives (econazole, miconazole and isoconazole) as test substances and hydroxypropyl-beta-CD as chiral selector. The results obtained by this method are in good agreement with those from non-linear least-square regression.