Modeling the electrophoretic mobility of analytes in binary solvent electrolyte systems in capillary electrophoresis using an artificial neural network.

An artificial neural network (ANN) methodology was used to model the electrophoretic mobility of basic analytes in binary solvent electrolyte systems. The electrophoretic mobilities in pure solvent electrolytes, and the volume fractions of the solvents in mixtures were used as input. The electrophoretic mobilities in mixed solvent buffers were employed as the output of the network. The optimized topology of the network was 3-3-1. 32 experimental mobility data sets collected from the literature were employed to test the correlation ability and prediction capability of the proposed method. The mean percentage deviation (MPD) between the experimental and calculated values was used as an accuracy criterion. The MPDs obtained for different numerical analyses varied between 0.21% and 13.74%. The results were also compared with similar calculated mobilities which were derived from the best multiple linear model from the literature. From these results it was found that the ANN methodology is superior to the multiple linear model.

Overview of the status and applications of capillary electrophoresis to the analysis of small molecules.

The status of capillary electrophoresis (CE) in the analysis of small molecules is reviewed and summarised with the illustrative use of recent literature references. Examples are cited in this review which demonstrate that CE is now a recognised and established technique in many industries, law courts and government regulatory agencies. Each of the principal areas of CE application in small molecule analysis are covered in sections which highlight the recent developments and possibilities within that area. Application areas include the analysis of pharmaceuticals, agrochemicals, chiral separations, and forensics is covered. This is an update to a previous review article [J. Chromatogr. A 856 (1999) 443] and covers papers published between 1999 and 2002. Technical developments and improvements, such as the advent of capillary array instrumentation for increased sample throughput, and improved detection options are described. Overall it is concluded that CE has become a recognised and established technique in many areas and is still within a period of development of both instrumentation and application which will continue to expand usage.

Enhanced pharmaceutical analysis by CE using dynamic surface coating system.

The poor repeatability of migration times in capillary electrophoresis (CE) within an injection sequence and between capillaries can be a difficulty when implementing CE for routine pharmaceutical analysis. The use of a dynamic surface coating has been shown to improve the routine performance of CE. The surface coating generates an appreciable electro-osmotic flow at low pH, which reduces analysis times for basic drugs compared to the low pH buffers typically used in CE. The repeatability of migration times and repeatability of migration times between capillaries was improved. Peak tailing for basic drugs was also reduced which improved peak shapes and peak area integration precision. It is concluded that the dynamic coating system is a positive advance in the routine implementation of CE into pharmaceutical analysis.

High-speed microemulsion electrokinetic chromatography.

In previous reports of microemulsion electrokinetic chromatography (MEEKC), analysis times were typically in the order of 10 min as high-ionic strength buffers were used. These buffers produced high currents which limit the voltages which can be applied, therefore, analysis times could not be reduced. The primary cause of the high-ionic strength is the relatively high concentrations of surfactants required to form the microemulsion. The surfactant concentration can be lower when using an oil with a smaller surface tension. This preliminary study showed that migration times in MEEKC can be reduced to below 1 min by using a combination of an optimum microemulsion composition, high voltage, high temperature, short capillaries by injecting via the "short end", or by simultaneously applying pressure and voltage. Long injection sequences and quantitation were found to be possible with minimum buffer depletion effects.

Selective and quantitative analysis of 4-hydroxybenzoate preservatives by microemulsion electrokinetic chromatography.

A microemulsion electrokinetic chromatography (MEEKC) method has been developed and validated for the determination of 4-hydroxybenzoates and their impurities. These materials are commonly known as parabens and are widely used as preservatives in foods, cosmetics and pharmaceuticals. The method was shown to be selective and quantitative for the methyl, ethyl, propyl and butyl esters of 4-hydroxybenzoic acid. An internal standard, 4-hydroxyacetophenone, was employed to improve injection precision and detector linearity. In addition, 4-hydroxybenzoic acid, the major degradent, could also be monitored at the 0.1% (m/m) level. The method was successfully validated for assay and detection of the impurities in 4-hydroxybenzoic acid methyl ester and 4-hydroxybenzoic acid propyl ester samples and for the determination of 4-hydroxybenzoic acid methyl ester in a liquid pharmaceutical formulation. The determination of paraben content by MEEKC in a liquid sample was consistent with HPLC analysis. This work is the first reported validated MEEKC method and shows that the methodology can be successfully implemented into routine quality control testing.

Background theory and applications of microemulsion electrokinetic chromatography.

Microemulsion electrokinetic chromatography (MEEKC) is an electrodriven separation technique. Separations are achieved using microemulsions which are nanometre-sized oil droplets suspended in aqueous buffer. The surface tension between the oil and water components is reduced by covered the oil droplet with an anionic surfactant such as sodium dodecyl sulphate and a co-surfactant such as a short-chain alcohol. This review summarises the various microemulsion types and compositions that have been used in MEEKC. The effects of key operating variables such as pH and temperature are also described. The application areas of MEEKC are also described in some detail. MEEKC has been applied to a wide range of water-soluble and insoluble both charged and neutral compounds. Examples are described which include analysis of derivatised sugars, proteins, pesticides and a wide range of pharmaceuticals. At present there are only a limited number of publications describing the use of MEEKC but it is anticipated that this number will increase rapidly in the near future as more awareness of the separation possibilities that MEEKC presents increases.

Overview of capillary electrophoresis and capillary electrochromatography.

This paper provides an overview on the current status of capillary electrophoresis (CE) and capillary electrochromatography (CEC). The focus is largely on the current application areas of CE where routine methods are now in place. These application areas include the analysis of DNA, clinical and forensic samples, carbohydrates, inorganic anions and metal ions, pharmaceuticals, enantiomeric species and proteins and peptides. More specific areas such the determination of physical properties, microchip CE and instrumentation developments are also covered. The application, advantages and limitations of CEC are covered. Recent review articles and textbooks are frequently cited to provide readers with a source of information regarding pioneering work and theoretical treatments.

Enantiomeric purity determination of propranolol by capillary electrophoresis using dual cyclodextrins and a polyacrylamide-coated capillary.

The use of a chirally selective capillary electrophoresis method is reported for the enantioselective purity determination of propranolol drug substance. The method employed a combination of both charged and neutral cyclodextrin. An internally coated capillary was used to suppress electroosmotic flow and potential peak tailing. The method was capable of monitoring below 0.1% m/m of the undesired impurity. Acceptable validation data was also obtained for recovery, linearity, and for both short and long-term injection precision.

Application of microemulsion electrokinetic chromatography to the analysis of a wide range of pharmaceuticals and excipients.

Microemulsion electrokinetic chromatography (MEEKC) is a capillary electrophoresis (CE) technique in which solutes partition with moving oil droplets present in a microemulsion buffer. Ionised species will also separate by electrophoresis. In this paper MEEKC is shown to give highly efficient and relatively rapid separations for a wide range of pharmaceuticals, vitamins and excipients. A single set of operating conditions was used to resolve both water-soluble and insoluble compounds. The method was also used to separate both ionic and neutral compounds. The method was especially useful in the analysis of water-insoluble neutral compounds such as steroids and lecithin, which are difficult to analyse by CE. The method was found to be both quantitative and highly repeatable. The quality of the separation was found to be dependent upon the sample diluent used if large injection volumes are employed. The use of MEEKC for the determination of complex mixtures such as multi-ingredient formulations and drug-related impurities was successfully demonstrated. MEEKC offers significant advantages over many forms of CE and capillary electrochromatography (CEC) and should be considered as an extremely useful option in pharmaceutical analysis.

Analysis of acidic compounds using capillary electrochromatography.

Capillary electrochromatography, CEC, is a hybrid of CE and HPLC and is rapidly gaining interest as a potential complementary technique. This paper provides an overview of literature concerning the separation of acidic compounds by CEC which fall into three distinct groups. These groups are those performed using capillaries packed with novel or unique stationary phases designed for CEC, and a smaller group where standard HPLC stationary phases packings such as ODS has been used. The third group involves the use of surface coated capillaries. This paper reviews the separation of acidic compounds by CEC and also includes a number of novel applications to illustrate the separation approaches and the analytical performance possible.

Separation of a range of cations by nonaqueous capillary electrophoresis using indirect and direct detection.

The use of nonaqueous media and indirect detection is reported for the separation and detection of a range of small cations. The novel applications involved separation of a range of metal ions, small nonchromophoric amines, cationic ion-pair reagents and cationic surfactants. Separations were achieved using acidified methanol containing imidazole as the UV co-ion for indirect detection. The methods produced different selectivity compared to aqueous methods using acidified aqueous imidazole solutions. Advantages of the methods include speed of analysis and prevention of sample micellerisation. The methods were shown to be quantitative and reproducible by their application to the determination of Tris content.

Optimisation, validation and application of a capillary electrophoresis method for the determination of ranitidine hydrochloride and related substances.

Ranitidine hydrochloride is an H2-antagonist which is widely prescribed for the treatment of peptic ulcers. The drug is marketed in a variety of dosage forms including tablets, syrups and injection solutions. A range of synthetic and degradative impurities of ranitidine are known and currently, these impurities are routinely determined using thin-layer chromatography (TLC). Alternatively a high-performance liquid chromatography (HPLC) method has also been employed in the assay of the pharmaceutical preparation. Unlike TLC, capillary electrophoresis (CE) offers the capability to quantify simultaneously both the active drug content and the levels of the related substances. The advantages of simplicity, selectivity, versatility and ease of use of CE offers a complementary separation technique to the established methods of HPLC and TLC in the determination of ranitidine and its related substances. This work represents a comprehensive evaluation of the performance of a developed CE method in the determination of drug-related impurities in both drug substance and various pharmaceutical formulations. The data obtained clearly shows that the performance of an optimised CE method can be equivalent in terms of sensitivity and precision to that of a HPLC method employed for a similar purpose and offers better selectivity against TLC and HPLC.

The use of microemulsion electrokinetic chromatography in pharmaceutical analysis.

The use of a single set of microemulsion electrokinetic chromatography (MEEKC) separation conditions has been assessed for its applicability in the analysis of a range of pharmaceutical compounds. Particular emphasis was placed on neutral or very hydrophobic compounds, which can be difficult to analyse by conventional capillary electrophoresis. The microemulsion employed for the majority of separations consisted of 0.81% w/w octane, 6.61% w/w 1-butanol, 3.31% w/w sodium dodecyl sulphate and 89.27% w/w 10 mM sodium tetraborate buffer. Good separations of methyl, ethyl, butyl and propyl hydroxybenzoates, and a range of ionic and neutral water soluble and insoluble compounds was achieved using a single set of separation conditions. A number of novel applications of MEEKC were developed included the simultaneous determination of the active components and preservatives in liquid formulation and determination of drug related impurities. Improved performance was obtained through use of internal standards and preparation of the samples dissolved in the microemulsion solution. Validation aspects such as linearity, repeatability, accuracy, injection precision and sensitivity were successfully assessed.

Development and optimisation of a generic micellar electrokinetic capillary chromatography method to support analysis of a wide range of pharmaceuticals and excipients.

A micellar electrokinetic capillary chromatography (MECC) method has been developed and validated to allow the analysis of a wide range of water soluble and insoluble acidic, basic and neutral drugs and excipients. An electronic database has been established to demonstrate the wide applicability of the method. The method has been validated and is now in routine use. In particular, acceptable injection precision is obtained through use of internal standards. Optimal sensitivity was obtained by using low UV wavelength detection. The method allows a number of cost and time saving benefits.

Rapid resolution of drugs and related substances with an eCAP polyamine coated capillary.

The long term stability of a commercial polyamine coated capillary (eCAP) is described. The capillary, which can be used in the CZE and MEKC mode, is based on coating with a polyamine after conditioning with 1 M NaOH and regeneration of this coating after each run. The stability was tested over 6 months on the drug trimethoprim and the R.S.D. values for migration time and peak area were 2.86 and 3.62% respectively (n = 8, each time of determination) (> 600 sample injections over the period). This stability was utilised in the validated method developed for trimethoprim and four of its related impurities. The repeatability of peak area for trimethoprim (without normalisation or external standard) was, within-day R.S.D. = 1.02% (n = 8) and between-days R.S.D. = 2.02% (n = 8 each day). Linearity was good (for 50 micrograms ml-1 target) (y = 249.6x + 17.3 (r = 0.992, n = 6). These results for trimethoprim and for other drug mixtures were comparison with conventional capillaries and the advantage of reducing the polyamine treated eCAP capillary to a minimum length is described, to achieve rapid assay of the 5 component timethoprim mixture in < 2 min.

Validated capillary electrophoresis method for the analysis of a range of acidic drugs and excipients.

A capillary electrophoresis (CE) method employing a high pH borate buffer has been validated to allow analysis of a wide range of acidic compounds including active drugs, pharmaceutical formulations, excipients, starting materials and intermediates. An internal database has been established to demonstrate the wide applicability of the method. The method has been extensively validated and is in routine use in a number of our laboratories worldwide. In particular, acceptable injection precision is obtained through the use of internal standards and the method robustness was evaluated using an experimental design. The method allows a number of cost and time saving benefits.

Quantitative determination of tryptophan enantiomers by capillary electrophoresis.

A novel capillary electrophoretic method is reported which allows efficient detection of 0.1% L-tryptophan in the presence of the D-enantiomer. The optimised conditions employed a triethanolamine-phosphoric acid electrolyte containing alpha-cyclodextrin. The method is also capable of acceptable injection precision resulting from the incorporation of an internal standard. The care and maintenance of the separation capillary are discussed. Acceptable validation criteria for sensitivity, precision, linearity, repeatability and recovery are included. The importance of including instrument-to-instrument method transfer in method validation is stressed and demonstrated.

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.

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.