Application of micellar electrokinetic chromatography to the quality control of pharmaceutical formulations: the analysis of xanthine derivatives

Investigations on the migration behaviour of purines and pyrimidines in capillary electromigration techniques with UV detection and mass spectrometric detection

Different approaches for the separation of a set of nucleosides and nucleobases using capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) are described. Several electrolyte compositions have been tested for this purpose. The addition of appropriate amounts of borate to the carrier electrolyte allowed manipulating migration orders in CZE and MEKC by selective complexation of the nucleosides. For detection either UV or two different modes of mass spectrometric (MS) detection were employed. The latter approach included a comparison of two ion sources namely electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) with respect to their potential in the detection of the selected compounds. Thereby it could be demonstrated that, in particular when it comes to the analysis of real samples, APPI-MS is the better choice if MS detection of purines and pyrimidines after separation by CZE is required.

Enhanced separation of purine and pyrimidine bases using carboxylic multiwalled carbon nanotubes as additive in capillary zone electrophoresis

This paper describes the enhanced separation of adenine (A), hypoxanthine (HX), 8-azaadenine (8-AA), thymine (T), cytosine (C), uracil (U) and guanine (G) by CZE dispersing carboxylic multiwalled carbon nanotubes (c-MWNTs) into the running buffer. The effect of important factors such as c-MWNT nanoparticle concentration, the acidity and concentration of running buffer, and separation voltage were investigated to acquire the optimum conditions. The seven purine and pyrimidine bases could be well separated within 16 min in a 35 cm effective length fused-silica capillary at a separation voltage of +8.0 kV in a 23 mM tetraborate buffer (pH 9.2) containing 8.0 x 10(-5) g/mL c-MWNTs. Under the optimal conditions, the linear ranges were of 2-250 microg/mL for A (R2 = 0.995), 3-200 microg/mL for U (R2 = 0.990) and G (R2 = 0.992), 3-250 microg/mL for T (R2 = 0.998), 2-200 microg/mL for C (R2 = 0.985) and 4-200 microg/mL for HX (R2 = 0.988) and 8-AA (R2 = 0.990). The detection limits were 0.9 microg/mL for A (S/N = 3), 2.4 microg/mL for U, 2.0 microg/mL for T, 1.5 microg/mL for C, 2.5 microg/mL for G and 3.0 microg/mL for HX and 8-AA. The proposed method was successfully applied for determining five purine and pyrimidine bases in yeast RNA.

Development of a HPTLC method for in-process purity testing of pentoxifylline

A HPTLC method for the separation and identification of pentoxifylline and related substances, impurities of reaction partners, and side reaction products has been developed using different mobile and stationary phases. For quantitative assay of possible by-products as impurities, LiChrospher RP-18 F254s chromatoplates, acetone-chloroform-toluene-dioxane (2:2:1:1 v/v) as a mobile phase, and detection at 275 nm were employed. Linearity (r > or = 0.997), recovery (86.5-115.5%), and determination limit (0.1-0.6%) were evaluated and found to be satisfactory. This method enables monitoring of the synthesis, as well as purity control of pentoxifylline-containing raw materials and pharmaceuticals.

High-performance capillary electrophoresis analysis of mate infusions prepared from stems and leaves of Ilex paraguariensis using automated micellar electrokinetic capillary chromatography

An automated micellar electrokinetic capillary chromatographic method has been developed in order to determine xanthines, e.g. caffeine, theobromine and theophylline, and chlorogenic acid in samples of yerba mate (Ilex paraguariensis). The target constituents were detected by photodiode array, and quantified by an external standard method. In addition, each constituent was collected separately and identified by EIMS. The method has been used to analyse 30 samples of mate infusions prepared at 30 and 75 degrees C with milled leaves and stems of 14 commercial brands which had been subjected to different elaboration processes. Suspended powdered material of each infusion was also analysed after three sieving steps. There was a remarkable difference in the relative xanthine composition of the finely suspended material, the amount of which varied according to the yerba mate brand, the elaboration process and the temperature of the infusion. The importance of these results with respect to gastrointestinal disorders which have been observed by habitual consumers of mate are discussed.

Electrophoretic behaviour of pharmacologically active alkylxanthines

The electrophoretic behaviour of ionizable and neutral alkylxanthines commonly used in pharmaceutical preparations was studied. The performance of various separation modes including capillary zone electrophoresis (CZE), cyclodextrin electrokinetic chromatography, and micellar electrokinetic chromatography (MEKC) with either sodium dodecyl sulfate (SDS) or bile salts as surfactants, was assessed. CZE in an alkaline medium successfully separates ionizable xanthines and dyphylline. The addition of carboxymethyl-beta-cyclodextrin to the background electrolyte allows only partial resolution of neutral xanthines. Based on MEKC results, bile salts exhibit more discrimination ability than SDS to separate similar xanthines. The best results are provided by taurodeoxycholic acid, which ensures baseline separation of xanthines.

Application of micellar electrokinetic chromatography to the quality control of a pharmaceutical preparation containing three bronchodilators

Theophylline(1,3-dimethylxanthine), dyphylline [7-(2,3-dihydroxypropyl)theophylline] and proxyphylline [7-(beta-hydroxypropyl)theophylline] are three bronchodilators administered jointly in a single pharmaceutical preparation used against asthma. A micellar electrokinetic chromatography (MEKC) method for their resolution using a background electrolyte consisting of 20 mM tetraborate at pH 8.5 and 100 mM sodium dodecyl sulfate is proposed. The method was used to determine the three active principles in a pharmaceutical preparation. The small amount of sample required and the expeditiousness of the procedure allow content uniformity to be determined in individual tablets. The values of the validation parameters for the method (viz. selectivity, linearity, accuracy, precision, limit of detection, limit of quantitation and robustness) are reported. A complete factor design (2(3)x2) including pH, the surfactant concentration and the ionic strength of the background electrolyte as factors was used to estimate robustness. Based on the results, the method is robust enough for quantitation purposes.

Stereoselective determination of R-(-)- and S-(+)-prilocaine in human serum by capillary electrophoresis using a derivatized cyclodextrin and ultraviolet detection

A capillary electrophoresis (CE) method for the quantification of R-(-)- and S-(+)-prilocaine in human serum was developed and validated. Stereoselective resolution was accomplished using 15 mM heptakis(2,6-di-methyl)-beta-cyclodextrin and 0.03 mM hexadecyltrimethylammonium bromide (HTAB) contained in 100 mM phosphate buffer, pH 2.5. Solid-phase extraction was used as a sample preparation technique to remove endogenous interferences. A 72-cm uncoated fused-silica capillary at a voltage of 25 kV and 30 degrees C was used for the analysis. The detection limits for R-(-)- and S-(+)-prilocaine were 38 ng/ml using 1 ml of human serum and the limits of quantitation were 45 ng/ml. The calibration curve was linear over the range of 45-750 ng/ml with procainamide as the internal standard. Precision and accuracy of the method were 2.86-8.50% and 3.29-7.40%, respectively, for R-(-)-prilocaine, and 3.94-9.17% and 2.0-6.73%, respectively, for S-(+)-prilocaine. The CE method was compared to an existing chiral HPLC method in terms of sensitivity and selectivity for the routine analysis of the drug.

Validated capillary electrophoretic method for the quantitative analysis of histamine acid phosphate and/or benzalkonium chloride

A novel capillary electrophoresis method has been developed and validated for the quantitative determination of histamine acid phosphate (HAP) and/or benzalkonium chloride (BKC). The solutes were separated using a pH 2.5 phosphate electrolyte with detection at 200 nm. Acceptable precision was obtained using internal standardisation. The method was also acceptable for determining levels of histidine which is an impurity in HAP. Profiling of BKC homologues was demonstrated for batch identity purposes. This method is used routinely and it is intended to register this method in the British Pharmacopoeia to supplement current test methods of TLC and HPLC.

Micellar electrokinetic chromatography perspectives in drug analysis

Micellar electrokinetic chromatography (MEKC) has become a popular mode among several capillary electromigration techniques. Most drug analyses can be performed by using MEKC because of its wide applicability. Enantiomer separation, separation of closely related peptides and isotopic compounds, separation of very complex mixtures, determination of drugs in the biological samples, etc., can be successfully achieved by MEKC. This review surveys typical applications of MEKC analysis. Recent advances in MEKC, especially with pseudo-stationary phases, are described. Modes of electrokinetic chromatography including MEKC, a separation theory of MEKC and selectivity manipulation in MEKC are also briefly mentioned.

Determination of drug-related impurities by capillary electrophoresis

The use of capillary electrophoresis (CE) to determine drug-related impurities is becoming established within industrial pharmaceutical analysis laboratories. Increasingly CE is being viewed as an alternative for, and complement to, high-performance liquid chromatography (HPLC). This paper comprehensively reviews the progress of CE in drug impurity determinations subdividing the reports into low pH, high pH and MECC applications. The section covering method performance and validation clearly shows that CE methods are capable of validation in this area and can often give equivalent performance to HPLC methods. Possible benefits of adopting CE for this testing include reductions in costs and improved robustness. Potential developments are covered including the use of electrolyte additives, instrumental developments and the increased implementation of electrochromatography. It is concluded that the current status of CE is sufficiently strong to allow the analyst to view CE as a viable and attractive alternative to HPLC.