Dual CD system-modified MEEKC method for the determination of clemastine and its impurities

A dual system of CDs was used for the first time in MEEKC with the aim of determining clemastine and its three main related impurities in both drug substances and tablets. The addition of methyl-β-cyclodextrin and heptakis(2,6-di-O-methyl)-β-cyclodextrin to the microemulsion pseudo-stationary phase was essential to increase the resolving power of the system to obtain a baseline separation among the compounds. The best microemulsion composition was identified by mixture design and the effects of the factors concentrations of CDs and voltage were investigated by a response surface study applying a Central Composite Design. In both cases, Derringer's desirability function made it possible to find the global optimum, which corresponded to the following combination: microemulsion, 89.8% 10 mM borate buffer pH 9.2, 1.5% n-heptane and 8.7% of SDS/n-butanol in 1:2 ratio; 18 mM methyl-β-cyclodextrin, 38 mM heptakis(2,6-di-O-methyl)-β-cyclodextrin, 17 kV. By applying these conditions, the separation was completed in about 5.5 min. The method was validated following International Conference on Harmonisation guidelines and was applied to a real sample of clemastine tablets.     

Separation of Biphenyl Nitrile Compounds by Microemulsion Electrokinetic Chromatography with Mixed Surfactants

A mixture of nine biphenyl nitrile compounds with high hydrophobicity and similar structures was successfully separated by microemulsion electrokinetic chromatography (MEEKC) within 30 rain. The buffer system contained 100 mmol/L sodium dodecyl sulfate (SDS), 80 mlnol/L sodium cholate (SC), 0.81% heptane, 7.5% n-butanol, 10% acetonitrile and 10 mmol/L borate. The addition of SC, organic modifiers, sample preparation and temperature all showedremarkable effect on the separation. Meanwhile, the MEEKC method was briefly compared with micellar electrokinetic chromatography (MEKC) method.     

Separation and determination of biphenyl nitrile compounds by microemulsion electrokinetic chromatography with mixed surfactants

A mixture of six biphenyl nitrile compounds and three related substances with high hydrophobicity and similar structures was successfully separated by microemulsion electrokinetic chromatography (MEEKC) within 30 min. The microemulsion system contained 100 mM sodium dodecyl sulfate (SDS), 80 mM sodium cholate (SC), 0.81% v/v heptane, 7.5% v/v n-butanol, 10% v/v acetonitrile, and 10 mM borate. The addition of SC, organic modifiers, sample preparation, and temperature all showed remarkable effects on the separation. The capacity factor (k) was calculated by using dodecyl benzene as the marker for microemulsion, and the calculated partition coefficient log P(o/w) of the solutes was in the range of 3.35-7.38. The log k values matched well with the log P(o/w) with a correlation coefficient of 0.96. In addition, the linear correlation coefficients of each compound between peak area and concentration were from 0.996 to 0.998 with the repeatability RSD value < 1.2% for migration time and < 4.8% for peak area, and the highest theoretic plate number was > 586000. MEEKC was compared with micellar electrokinetic chromatography (MEKC) indicating that the former method is more suitable for this separation and can be used for the quality control of biphenyl nitrile compounds in the synthesis of liquid crystals.     

Microemulsion electrokinetic chromatography of corticosteroids. Effect of surfactants and cyclodextrins on the separation selectivity

The separation of neutral hydrophobic corticosteroids (cortisone, cortisone acetate, hydrocortisone, hydrocortisone acetate, prednisolone and prednisolone acetate) by microemulsion electrokinetic chromatography (MEEKC) was studied. In the preparation of microemulsion, heptane was the solvent, n-butanol the co-surfactant and, as anionic surfactants, sodium dodecyl sulfate (SDS) or taurodeoxycholic acid sodium salt (STDC) were employed. Using an acidic running buffer, (phosphate pH 2.5) a strong suppression of the electroosmotic flow (EOF) was observed; this resulted in a fast anodic migration of the analytes partitioned into the negatively charged microemulsion droplets. Under these conditions, STDC showed better separation of corticosteroids than the conventional SDS; however, the use of a single anionic surfactant did not provide the required selectivity. The addition of the neutral surfactant polyoxyethylene glycol octadecyl ether (Brij 76) significantly altered the migration of each analytes allowing a better tuning of separation; however, in order to obtain adequate resolution between couples of adjacent critical peaks, the addition of neutral cyclodextrins (CDs) was found to be essential. This apparently complex system (CD-MEEKC), was optimized by studying the effect of the most important parameters affecting separation: STDC concentration, Brij 76 concentration, nature and concentration of cyclodextrins. Following a rational step-by-step approach, the optimised conditions providing the complete separation of the analytes were found to be: 4.0% STDC, 2.5% Brij 76, 6.6% n-butanol, 1.36% heptane and 85.54% of a solution 5 mM beta-CD in 50 mM phosphate buffer (pH 2.5). The optimized system was preliminary applied to the detection of corticosteroids related substances at impurity level and it could be considered a useful orthogonal alternative to HPLC methods.     

Comparing micellar electrokinetic chromatography and microemulsion electrokinetic chromatography for the analysis of preservatives in pharmaceutical and cosmetic products

In this study, separation and determination of nine preservatives ranging from hydrophilic to hydrophobic properties, which are commonly used as additives in various pharmaceutical and cosmetic products, by micellar electrokinetic chromatograpy (MEKC) and microemulsion electrokinetic chromatography (MEEKC) were compared. The effect of temperature, buffer pH, and concentration of surfactant on separation were examined. In MEKC, the separation resolution of preservatives improved markedly by changing the sodium dodecyl sulfate concentration. Temperature and pH of running buffers were used mainly to shorten the magnitude of separation time. However, in order to detect all preservatives in a single run in a MEEKC system, a microemulsion of higher pH was needed. The separation resolution was improved dramatically by changing temperature, and a higher concentration of SDS was necessary for maintaining a stable microemulsion solution, therefore the separation of the nine preservatives in MEEKC took longer than in MEKC. An optimum MEKC method for separation of the nine preservatives was obtained within 9.0 min with a running buffer of pH 9.0 containing 20 mM SDS at 25 degrees C. A separation with baseline resolution was also obtained within 16 min using a microemulsion of pH 9.5 which composed of SDS, 1-butanol, and octane, and a shorter capillary column at 34 degrees C. Finally, the developed MEKC and MEEKC methods determined successfully preservatives in various cosmetic and pharmaceutical products.     

Microemulsion electrokinetic chromatography for separation and analysis of curcuminoids in turmeric samples

Microemulsion EKC (MEEKC) was developed for quantitative analysis of curcuminoids, such as curcumin (C), demethoxycurcumin (D), and bis-demethoxycurcumin (B). MEEKC separation of curcuminoids was optimized, and a change in resolution was explained using a modified equation for resolution in MEEKC without electroosmosis. The suitable MEEKC conditions for separation of curcuminoids were obtained to be the microemulsion buffer containing 50 mM phosphate buffer at pH 2.5, 1.1% v/v n-octane as oil droplets, 180 mM SDS as surfactant, 890 mM 1-butanol as cosurfactant, and 25% v/v 2-propanol as organic cosolvent; applied voltage of -15 kV; and separation temperature 25 degrees C. Achieved baseline resolution of C:D and D:B was obtained with R(s) -2.4 and analysis time within 18 min. In addition, high accuracy and precision of the method were obtained. This MEEKC method was used for quantitative determination of individual curcuminoids in medicinal turmeric capsules and powdered turmeric used as coloring additive in food, with simple sample preparation such as solvent extraction, dilution, and filtration, and without cleaning up by SPE.     

Enhanced separation of Compound Xueshuantong capsule using functionalized carbon nanotubes with cationic surfactant solutions in MEEKC

A novel additive of multi‐walled carbon nanotubes (MWNTs) dispersed with cationic surfactants or mixed cationic/anionic surfactants was used for MEEKC separation of eight phenolic compounds, four glycosides, and one phenanthraquinone. In this context, several parameters affecting MEEKC separation were studied, including the dispersion agents of MWNTs, MWNTs content, oil type, SDS concentration, and the type and concentration of cosurfactant. Compared with conventional MEEKC, the addition of all types of MWNTs dispersions using single or mixed cationic surfactant solutions in running buffers was especially useful for improving the separation of solutes tested, as they influenced the partitioning between the oil droplets and aqueous phase due to the exceptional electrical properties and large surface areas of MWNTs. Use of cationic surfactant‐coated MWNTs (6.4 μg/mL) as the additive in a microemulsion buffer (0.5% octanol, 2.8% SDS, 5.8% isopropanol, and 5 mM borate buffer) yielded complete resolution of 13 analytes. The proposed method has been successfully applied for the detection and quantification of the studied compounds in a complex matrix sample (Compound Xueshuantong capsule).     

Separation of hydrophobic polymer additives by microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) has been applied to the separation of some phenolic antioxidants [Irganox 1024, Irganox 1035, Irganox 1076, Irganox 1010, Irganox 1330, Irgafos 138, Irganox 168 and 2,6-di-tert.-butyl-4-methylphenol (BHT)]. Due to the extremely hydrophobic nature of these analytes, they could not be separated using standard MEEKC conditions and two alternative approaches were investigated. Using an acidic buffer (phosphate, pH 2.5) to effectively suppress the electroosmotic flow, the addition of 2-propanol to the aqueous phase of the microemulsion buffer to improve partitioning of the analytes, and a negative separation voltage, separation of five of the analytes in under 10 min was possible. The second approach, using a basic buffer (borate, pH 9.2) and a positive separation voltage resulted in complete resolution of all eight analytes. A mixed surfactant system comprising the anionic sodium dodecyl sulfate (SDS) and neutral Brij 35 was used to reduce the overall charge and with it the mobility of the droplets, and hence the separation time. Using an optimised MEEKC buffer consisting of 2.25% (w/w) SDS, 0.75% (w/w) Brij 35, 0.8% (w/w) n-octane, 6.6% (w/w) 1-butanol, 25% (w/w) 2-propanol and 64.6% (w/w) 10 mM borate buffer (pH 9.2) the eight target analytes were baseline separated in under 25 min. For these analytes, MEEKC was found to be superior to micellar electrokinetic chromatography in every respect. Specifically, the solubility of the analytes was better, the selectivity was more favourable, the analysis time was shorter and the separation efficiency was up to 72% higher when using the MEEKC method. Detection limits from 5.4 to 26 microg/ml were obtained and the calibration plot was linear over more than one order of magnitude. The optimised method could be applied to the determination of Irganox 1330 and Irganox 1010 in polypropylene.     

Comparison of oil-in-water and water-in-oil microemulsion electrokinetic chromatography as methods for the analysis of eight phenolic acids and five diterpenoids

Oil-in-water (O/W) and water-in-oil (W/O) MEEKC were compared for their abilities to separate and detect eight phenolic acids and five diterpenoids in Radix et Rhizoma Salviae Miltiorrhizae (RRSM). The effects of oil type and concentration, organic modifier, SDS, and buffer concentration on separation were examined in order to optimize the two methods. Oil contents and organic modifier were found to markedly influence the separation selectivity for both O/W and W/O systems. SDS concentration rarely affected separation resolution for O/W MEEKC, and separation of eight phenolic acids and five diterpenoids could be improved by changing the buffer concentration for W/O MEEKC. A highly efficient O/W MEEKC separation method, where the 13 compounds were separated with baseline resolution, was achieved by using a microemulsion solution of pH 8.0 containing 0.6% cyclohexane, 3.0% SDS, 6.0% 1-butanol, and 3.0% ACN. The W/O MEEKC was unable to resolve all the components. In addition, the analytic time in O/W MEEKC was shorter than that in W/O MEEKC. Finally, the developed O/W MEEKC method was successfully applied to determine analytic compounds in RRSM samples.     

Microemulsion electrokinetic capillary chromatography of sulfated disaccharides derived from glycosaminoglycans.

Microemulsion electrokinetic capillary chromatography (MEEKC) is a capillary electrophoresis technique in which neutral and ionized species can be resolved according to their partitioning into moving oil droplets present in the operating buffer. In this report, we present for the first time the application of MEEKC in the analysis of glycosaminoglycans. An efficient method for the separation of the variously sulfated delta-disaccharides obtained following digestion of chondroitin and dermatan sulfates with chondro/ dermato lyases and derivatization with 2-aminoacridone is described. Nonsulfated, mono-, di-, and trisulfated delta-disaccharides were completely separated using the microemulsion octane/butan-1-ol/Sodium dodecyl sulfate (SDS) in 10 mM borate buffer, pH 9.3, at 25 kV. Agreement of the obtained disaccharide composition with literature values showed that MEEKC can be used for the analysis of glycosaminoglycans.     

Simultaneous determination of natural and synthetic estrogens by EKC using a novel microemulsion

A novel microemulsion based on sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was developed for the simultaneous determination of natural and synthetic estrogens by microemulsion EKC (MEEKC). The microemulsion system consisted of 1.4% w/w AOT, 1.0% w/w octane, 7.0% w/w 1-butanol and 90.6% w/w 20 mM sodium salt of 3-(cyclohexylamino)-2-hydroxy-1-propanesulfonic acid (CAPSO) and 10 mM phosphate buffer at pH 12.5. A baseline resolution in the separation of estrone, 17beta-estradiol, estriol, estradiol 17-hemisuccinate, etinilestradiol, estradiol 3-benzoate, and estradiol 17-valerate was achieved in comparison to the traditional MEEKC system with SDS in less than 15 min. The optimized electrophoretic conditions included the use of an uncoated-silica capillary of 60 cm of total length and 75 microm id, an applied voltage of 25 kV, a temperature of 25 degrees C and 214 UV-detection. Parameters of validation such as specificity, linearity, accuracy, LOD, LOQ and robustness were evaluated according to international guidelines. Due to its simplicity, accuracy, and reliability, the proposed method can be an advantageous alternative to the traditional methodologies for the analysis of natural and synthetic estrogens in different pharmaceutical forms.     

微乳液毛细管电动色谱法快速测定消炎利胆片中的穿心莲内酯和脱水穿心莲内酯

建立了微乳液毛细管电动色谱同时分析消炎利胆片中穿心莲内酯和脱水穿心莲内酯的方法。考察了缓冲溶液的浓度、pH值、十二烷基硫酸钠(SDS)以及助表面活性剂的含量对分离测定的影响。在由乙酸乙酯-SDS-正丁醇-30 mmol/L硼砂缓冲液(pH 9.5)（质量比为0.5∶0.6∶6.0∶92.9）组成的微乳液体系中,两种内酯在6 min内完成分离。该法简便、快速、选择性好,用于实际样品中穿心莲内酯和脱水穿心莲内酯的分析,获得了满意的结果。     

A comparative study of micellar and microemulsion EKC for the analysis of benzoylurea insecticides and their analogs

An investigation of the basic factors which govern the microemulsion EKC (MEEKC) and MEKC for the separation of four benzoylurea (BU) insecticides and their four analogs was carried out. In MEEKC, the separation of eight BU compounds was optimized by changing the microemulsion composition, such as concentration of SDS, octane, n-butanol, and isopropanol percentages, as well as capillary temperature. Separation optimization was also carried out for MEKC, showing that ACN and a high level of another additive gamma-CD were needed to achieve effective separation of these analytes. Although separation with baseline resolution was achieved by either MEEKC or MEKC methods, the separation selectivity resulting from the proposed MEEKC method was completely different from that of MEKC. In addition, analytical time in MEEKC was longer than that in MEKC, but in view of theoretical plate numbers, detection limits, and reproducibility, both methods were effective for the analysis of BU insecticides and their analogs.     

Retention modelling in liquid chromatographic separation of simvastatin and six impurities using a microemulsion as eluent

A novel and unique approach was used for retention modelling in the separation of simvastatin and six impurities by liquid chromatographic using a microemulsion as mobile phase. A microemulsion is a modification of a micellar system where a lipophilic organic solvent is dissolved in the micelles; for that reason, microemulsions are usually treated as solvent-modified micellar solutions. When microemulsions are used as eluents in HPLC separations, solutes partition between the charged oil droplets and the aqueous buffer phase. The complexity of the composition of the microemulsion permits extensive manipulations to be made during method development in order to achieve acceptable resolution of such a complex mixture of substances. In order to avoid a laborious "trial and error" procedure, a 2(3) full factorial design was applied for choosing an optimal microemulsion composition to obtain good separation in a reasonable run time. Organic solvent, sodium dodecyl sulphate, and n-butanol content were varied within defined experimental domain. Optimal conditions for the separation of simvastatin and its six impurities were obtained using an X Terra 50 x 4.6 mm, 3.5 microm particle size column at 30 degrees C. The mobile phase consisted of 0.9% w/w of diisopropyl ether, 2.2% w/w of sodium dodecylsulphate (SDS), 7.0% w/w of co-surfactant such as n-butanol, and 89.9% w/w of aqueous 25 mM disodium phosphate pH 7.0.     

Development and optimization of an analytical method for the determination of UV filters in suntan lotions based on microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) has been applied to the separation of some UV filters (Eusolex 4360, Eusolex 6300, Eusolex OCR, Eusolex 2292, Eusolex 6007, Eusolex 9020, Eusolex HMS, Eusolex OS, and Eusolex 232) commonly found in suntan lotions. The composition of the microemulsion employed was optimized with respect to the best possible separation of the selected analytes using artificial neural networks (ANNs). Two parameters namely the composition of the mixed surfactant system comprising the anionic sodium dodecyl sulfate (SDS) and neutral Brij 35 and the amount of organic modifier (2-propanol) present in the aqueous phase of the microemulsion were modeled. Using an optimized MEEKC buffer consisting of 2.25 g SDS, 0.75 g Brij 35, 6.6 g 1-butanol, 0.8 g n-octane, 17.5 g 2-propanol, and 72.1 g of 10 mM borate buffer (pH 9.2), eight target analytes could be separated in under 25 min employing a diode-array detector to segregate the overlapping signals obtained for Eusolex 9020 and Eusolex HMS. Detection limits from 0.8 to 6.0 nug/mL were obtained and the calibration plots were linear over at least one order of magnitude. The optimized method could be applied to the determination of Eusolex 6300 and Eusolex 9020 in a commercial suntan lotion.     

Comparison of HPLC and MEEKC for Miconazole Nitrate Determination in Pharmaceutical Formulation

A simple solid phase extraction (SPE) method coupled with high performance liquid chromatography (HPLC) using UV detector and microemulsion electrokinetic chromatography (MEEKC) has been developed and compared for the quantitative determination of miconazole nitrate in pharmaceutical formulation. For HPLC method, two parameters were optimized, namely, the wavelength and the mobile phases. The optimized condition was at the 225 nm wavelength and the mobile phase of ACN:MeOH (90:10 v/v). There are seven MEEKC parameters that were optimized, in this research, which were applied to voltage, temperature, wavelength, sodium dodecyl sulfate (SDS) concentration, buffer pH, buffer concentration and butan-1-ol concentration. The optimum MEEKC condition was obtained using 86.35 % (w/w) 2.5 mM borate buffer pH 9, 0.25 % (w/w) SDS, 0.8 % (w/w) ethyl acetate, 6.6 % w/w butan-1-ol and 6.0 % (w/w) acetonitrile. The combination of SPE using a diol column with HPLC–UV and the MEEKC methods were successfully applied for the determination of miconazole nitrate in a pharmaceutical formulation with the recovery percentage of 98.35 and 92.50 %, respectively.

     

Separation of corticosteroids by microemulsion EKC with diethyl L-tartrate as the oil phase

A novel microemulsion based on a mixture of diethyl L-tartrate (DET) and SDS was developed for the microemulsion EKC (MEEKC) determination of structurally related steroids. The system consisted of 0.5% w/w DET, 1.7% w/w SDS, 1.2% w/w 1-butanol, 89.6% w/w phosphate buffer (40 mM, pH 7.0), and 7% w/w ACN. With an applied voltage of +10 kV, a baseline separation of aldosterone (A), cortisone acetate (CA), dexamethasone (D), hydrocortisone (H), hydrocortisone acetate (HA), prednisolone (P), prednisolone acetate (PA), prednisone (Ps), triamcinolone (T), and triamcinolone acetonide (TA) could be achieved. Under the optimized conditions, the reproducibility of the retention time (n = 4) for most of the compounds was less than +/-0.8% with the exception of A, Ps, and T. The average number of theoretical plates was 18 800 plates/m. The results were compared with those achieved by the modified micellar EKC (MEKC). MEEKC showed obvious advantages over MEKC for the separation of highly hydrophobic substances. To further evaluate the system, we tested the MEEKC method by analyzing corticosteroids in a spiked urine sample.     

Comparison of HPLC and MEEKC for Miconazole Nitrate Determination in Pharmaceutical Formulation

A simple solid phase extraction (SPE) method coupled with high performance liquid chromatography (HPLC) using UV detector and microemulsion electrokinetic chromatography (MEEKC) has been developed and compared for the quantitative determination of miconazole nitrate in pharmaceutical formulation. For HPLC method, two parameters were optimized, namely, the wavelength and the mobile phases. The optimized condition was at the 225 nm wavelength and the mobile phase of ACN:MeOH (90:10 v/v). There are seven MEEKC parameters that were optimized, in this research, which were applied to voltage, temperature, wavelength, sodium dodecyl sulfate (SDS) concentration, buffer pH, buffer concentration and butan-1-ol concentration. The optimum MEEKC condition was obtained using 86.35 % (w/w) 2.5 mM borate buffer pH 9, 0.25 % (w/w) SDS, 0.8 % (w/w) ethyl acetate, 6.6 % w/w butan-1-ol and 6.0 % (w/w) acetonitrile. The combination of SPE using a diol column with HPLC–UV and the MEEKC methods were successfully applied for the determination of miconazole nitrate in a pharmaceutical formulation with the recovery percentage of 98.35 and 92.50 %, respectively.     

Separation of isomers of dienoic acids by electromigration techniques

Different capillary electromigration techniques were employed to resolve geometrical isomers of sorbic acid, decadienoic acid, and ethyl sorbate. Since these substances differ in their polarity, shape, and size, various electromigration approaches were investigated to separate the four geometrical isomers of each compound. With capillary electrophoresis (CE) modified with a cyclodextrin (β‐CD) the four isomers of sorbic acid were separated using a buffer that consists of 60 mM tetraborate and 8 mg/mL β‐CD. The separation of decadienoic acid geometrical isomers was not possible, even at elevated tetraborate and cyclodextrin concentrations. The four isomers of decadienoic acid were successfully separated using micellar electrokinetic chromatography (MEKC) with a buffer consisting of 30 mM tetraborate and 100 mM SDS and microemulsion electrokinetic chromatography (MEEKC). Ethyl sorbate is the least polar of all the studied substances and its isomers could not be separated by MEKC or MEEKC. The resolution was improved and isomers were fully separated using capillary electrochromatography (CEC) with ODS stationary phase and a mobile phase consisting of 10 mM boric acid in 50% acetonitrile. Minor differences in the polarity and the shape of isomers and high resolving power of the applied techniques were sufficient for separation of very similar compounds. We have shown that versatile electromigration techniques can be applied for separation of geometrical isomers of dienoic acids and their esters.     

Micellar electrokinetic chromatography for the simultaneous determination of ketorolac tromethamine and its impurities. Multivariate optimization and validation

A simple, fast and selective micellar electrokinetic chromatographic (MEKC) method for the simultaneous assay of ketorolac tromethamine and its known related impurities (1-hydroxy analog of ketorolac, 1-keto analog of ketorolac and decarboxylated ketorolac), in both drug substance and coated tablets, is described. The compounds were detected at 323 nm, and flufenamic acid (FL) and tolmetin (TL) were chosen as internal standards to quantify ketorolac tromethamine and impurities, respectively. The multivariate optimization of the experimental conditions was carried out by means of the response surface study, considering as responses the resolution values and analysis time. The optimized background electrolyte (BGE) consisted of a mixture of 13 mM boric acid and phosphoric acid, adjusted to pH 9.1 with 1 M sodium hydroxide, containing 73 mM sodium dodecyl sulfate (SDS). Optimal temperature and voltage were 30 degrees C and 27 kV. Applying these conditions, all compounds were resolved in about 6 min. The related substances could be quantified up to the 0.1% (w/w) level. Validation was performed, either for drug substances and drug product, evaluating selectivity, robustness, linearity and range, precision, accuracy, detection and quantitation limits and system suitability.