Pharmaceutical applications of micelles in chromatography and electrophoresis

Analytical capabilities of micellar liquid chromatography and application to residue and contaminant analysis: A review

Green chemistry is the use of chemistry to reduce or eliminate the use of generation of feedstocks, products, by-products, solvents, reagents, etc. that are hazardous to human health or the environment. One of the branches of green chemistry is micellar liquid chromatography. Micellar liquid chromatography is a reversed-phase liquid chromatographic mode with mobile phases containing a surfactant above its critical micellar concentration. The applications of micellar liquid chromatography for the determination of numerous compounds in pharmaceutical formulation, biological samples, food, environmental samples, and feeds have been growing rapidly. Micellar liquid chromatography technique has several advantages over other chromatographic techniques. Its main advantage is the small amount of organic modifiers used such as acetonitrile and methanol and the safety and recyclability of the mobile phase. In our work, we discuss the development of "green chemistry" and present what micellar liquid chromatography is. This article presents application methods with the use of micellar liquid chromatography for analysis on antibacterial substances, melamine, biogenic amines, plant protection products, flavonoids, as well as peptides in biological matrices such as milk, eggs, tissues, honey, and feed.

Consensus-based comparison of chromatographic and computationally estimated lipophilicity of benzothiepino[3,2-c]pyridine derivatives as potential antifungal drugs

Lipophilicity is one of the essential properties influencing drug absorption, excretion and metabolism. It is used for screening viable drug candidates. Chromatographic behavior of thiepino[3,2-c:6,7-c']dipyridine and 16 benzothiepino[3,2-c]pyridine derivatives as potential antifungal drugs was studied using thin-layer chromatography under typical reversed-phase conditions and two microemulsion chromatographic systems. Seventeen chromatographic and nine in silico lipophilicity measures were estimated. They were compared by classical multivariate approaches: principal component analysis, hierarchical cluster analysis, and ranked and grouped by the non-parametric method-Sum of ranking differences. Two computational and two chromatographic descriptors from the typical reversed-phase conditions using acetone/water mixtures emerged as the best candidates for lipophilicity estimation. The principal component scores related to typical reversed-phase conditions using dioxane/water were ranked as statistically insignificant (the worst). Microemulsion systems were positioned in between, performing worse than in silico estimates. Thiepine derivatives were ranked and grouped by sum of ranking differences, fusing multiple lipophilicity measures. In multicriteria maximization ranking, the compound substituted by phenyl group at position 8 was selected as the most lipophilic one. It is also the most active against Candida albicans. The ranking confirmed that introduction of phenyl core is essential for increasing the lipophilicity of the studied compounds.

Multivariate assessment of lipophilicity scales-computational and reversed phase thin-layer chromatographic indices

Needs for fast, yet reliable means of assessing the lipophilicities of diverse compounds resulted in the development of various in silico and chromatographic approaches that are faster, cheaper, and greener compared to the traditional shake-flask method. However, at present no accepted "standard" approach exists for their comparison and selection of the most appropriate one(s). This is of utmost importance when it comes to the development of new lipophilicity indices, or the assessment of the lipophilicity of newly synthesized compounds. In this study, 50 well-known, diverse compounds of significant pharmaceutical and environmental importance have been selected and examined. Octanol-water partition coefficients have been measured with the shake-flask method for most of them. Their retentions have been studied in typical reversed thin-layer chromatographic systems, involving the most frequently employed stationary phases (octadecyl- and cyano-modified silica), and acetonitrile and methanol as mobile phase constituents. Twelve computationally estimated logP-s and twenty chromatographic indices together with the shake-flask octanol-water partition coefficient have been investigated with classical chemometric approaches-such as principal component analysis (PCA), hierarchical cluster analysis (HCA), Pearson's and Spearman's correlation matrices, as well as novel non-parametric methods: sum of ranking differences (SRD) and generalized pairwise correlation method (GPCM). Novel SRD and GPCM methods have been introduced based on the Comparisons with One VAriable (lipophilicity metric) at a Time (COVAT). For the visualization of COVAT results, a heatmap format was introduced. Analysis of variance (ANOVA) was applied to reveal the dominant factors between computational logPs and various chromatographic measures. In consensus-based comparisons, the shake-flask method performed the best, closely followed by computational estimates, while the chromatographic estimates often overlap with in silico assessments, mostly with methods involving octadecyl-modified silica stationary phases. The ones that employ cyano-modified silica perform generally worse. The introduction of alternative coloring schemes for the covariance matrices and SRD/GPCM heatmaps enables the discovery of intrinsic relationships among lipophilicity scales and the selection of best/worst measures. Closest to the recommended logKOW values are ClogP and the first principal component scores obtained on octadecyl-silica stationary phase in combination with methanol-water mobile phase, while the usage of slopes derived from Soczewinski-Matyisik equation should be avoided.

Towards better understanding of lipophilicity: assessment of in silico and chromatographic logP measures for pharmaceutically important compounds by nonparametric rankings

Lipophilicity is one of the most frequently used physicochemical properties that affects compound solubility, determines its passive transport through biological membranes, influences biodistribution, metabolism and pharmacokinetics. We compared, ranked and grouped chromatographic lipophilicity indices and computationally estimated logP-s by sensitive and robust non-parametric approaches: sum of ranking differences (SRD) and generalized pairwise correlation method (GPCM). Chromatographic indices of fourteen neurotoxins and twenty one 1,2,4-triazole compounds have been derived from typical reversed-phase thin-layer chromatography and micellar chromatography. They were compared with in silico estimated logP-s. Under typical reversed-phase conditions, octadecyl-, octyl-, and cyanopropyl-modified silica have clear advantage over ethyl-, aminopropyl-, and diol-modified beds, i.e., the preferable choice of the stationary phase follows this order: octadecyl>octyl>cyanopropyl>ethyl>octadecylwettable>aminopropyl>diol. Many of these indices outperform the majority of computationally estimated logP-s. Clear distinction can be made based on cross-validation and statistical tests. Oppositely, micellar chromatography may not be successfully used for the lipophilicity assessment, since retention parameters obtained from the typical reversed-phase conditions outperform the parameters obtained by micellar chromatography. Both ranking approaches, SRD and GPCM, although based on different background, provide highly similar variable ordering and grouping leading to the same, above mentioned conclusions. However, GPCM results in more degeneracy, i.e., in some cases it cannot distinguish the lipophilicity parameters whereas SRD and its cross-validated version can. On the other hand GPCM produces a more characteristic grouping. Both methods can be successfully used for selection of the most and least appropriate lipophilicity measures.

Molecular dynamic simulations of self-assembly of amphiphilic comb-like anionic polybenzoxazines

Fully atomistic molecular dynamic simulations were performed to address the self-assembly of amphiphilic and comb-like polybenzoxazines (iBnXz) in water, with i = 3 (trimer), i = 4 (tetramer); i = 6 (hexamer), i = 8 (octamer), and i = 10 (decamer). Spontaneous aggregation of these comb-like polybenzoxazine molecules into a single micelle occurs in the simulations. The simulations show that molecular size and concentration play important roles in micellar morphology. At an iBnXz concentration of 50 mM, the 3BnXz and 4BnXz molecules aggregate into spherical micelles, whereas the 6BnXz, 8BnXz, and 10BnXz molecules aggregate into cylindrical micelles. The micellar morphology is spherical at low concentrations, but undergoes a transition to cylindrical shape as concentration increases. The transition point depends on the molecular size-both the true size as indicated by molecular weight, as well as an additional effective size dependent on molecular flexibility.

Unique effects of aerosol OT lamellar structures on the dynamics of guest molecules

The behavior of lamellar structures of Aerosol OT (AOT) as hosts, vis-à-vis the flexible normal micelles and rigid nanochannels of Nafion membranes, has been investigated with two different fluorophores, [2,2'-bipyridyl]-3,3'-diol (BP(OH)2) and coumarin 102 (C102). Surprisingly, for BP(OH)2, a rise time is observed at intermediate emission wavelengths and not in the red edge of the fluorescence spectrum. A shoulder at 525 nm is observed in time resolved emission spectra (TRES) at initial times of BP(OH)2 in AOT lamellar structures. This feature is the signature of the monoketo (MK) tautomer, observed for the first time in a microheterogeneous medium. Also, the usually ultrafast single proton transfer in BP(OH)2 is retarded to an considerable extent in lamellar structures. The potential of this medium in promoting unusual intermediates is thus highlighted. This property may be ascribed to the rigidity of lamellar structures, compared to hosts such as regular micelles. However, studies using another fluorophore, coumarin 102 (C102), brings out the fact that these structures are significantly different from the rigid host, Nafion, as well. The absence of excited state proton transfer (ESPT) in this molecule in AOT lamellar structures indicates that it is not protonated, unlike in Nafion. Thus, the interfacial pH of lamellar structures is found to be significantly greater than that of Nafion nanochannels. From the time dependent Stokes shift (TDSS) of the emission spectra of C102, the relaxation time (0.85 ns) of interfacial water in lamellar structures is found to be an order of magnitude faster than that observed in Nafion nanochannels, in which H3O(+) ions have been substituted by different cations. Hence, this study demonstrates that AOT lamellar structures are rather unique hosts and that they behave very differently from conventional rigid and flexible hosts such as normal micelles and Nafion, respectively.

Formation and degradation of multicomponent multicore micelles: insights from dissipative particle dynamics simulations

Dissipative particle dynamics (DPD) simulation is employed to examine (i) the multicomponent multicore micelle (MMM) formation from two kinds of star-shaped copolymers: A2B4B4 and C2B4B4 where A, B, and C are the segments of the copolymers and (ii) the degradation of multicomponent multicore micelles. Regarding the micelle formation, single-core micelles with the core composed of two components (SCII), multicomponent multicore micelles with each core composed of two components (MMII), multicomponent multicore micelles with each of the cores composed of one component (MMI), and multicomponent multicore rod micelles (MMRI) are considered. By changing the ratio between the number of segments of one of the polymers and the total number of segments of the two copolymers, the number of cores generated and their composition can be controlled. Considering that only C2B4B4 is degraded to 2C1 + 2B4, it was found that SCII, MMII, and MMI micelles degraded to a single irregular network core, to multicores with cores formed of loose aggregates, and to multicore micelles, respectively. The dynamics of micelle formation has several stages (small aggregates (nuclei) → growth of aggregates → micellization) whereas the dynamics of degradation involves the diffusion of the degraded components inside and outside micelles and the rearrangement of the cores of the micelles into new cores.

Quantification of Lipophilicity of 1,2,4-Triazoles Using Micellar Chromatography

High-performance liquid chromatography (HPLC), over-pressured-layer chromatography (OPLC) and thin-layer chromatography (TLC) techniques with micellar mobile phases were proposed to evaluate the lipophilicity of 21 newly synthesized 1,2,4-triazoles, compounds of potential importance in medicine or agriculture as fungicides. Micellar parameters log k(m) were compared with extrapolated R(M0) values determined from reversed-phase (RP) TLC experimental data obtained on RP-8 stationary phases as well as with log P values (Alog Ps, AClog P, Alog P, Mlog P, KowWin, xlog P2 and xlog P3) calculated from molecular structures of solutes tested. The results obtained by applying principal component analysis (PCA) and linear regression showed considerable similarity between partition and retention parameters as alternative lipophilicity descriptors, and indicated micellar chromatography as a suitable technique to study lipophilic properties of organic substances. In micellar HPLC, RP-8e column (Purospher) was applied, whereas in OPLC and TLC, RP-CN plates were applied, which was the novelty of this study and allowed the use of micellar effluents in planar chromatography measurements.

Micellar electrokinetic chromatography for the determination of cortisol in urine samples in view of biomedical studies

An MEKC method used for the determination of cortisol in urine was developed and elaborated. In turn, the measurements of urinary free cortisol provided the diagnostic information for excess adrenal production of cortisol. MEKC realized by the addition of anionic surfactant SDS to the buffer solution was demonstrated to be the appropriate mode for the separation of cortisol and dexamethasone was used as internal standard. A buffer solution composed of 10 mM sodium tetraborate and 50 mM SDS at pH 8.8 was used. The MEKC assay was evaluated by analyzing a series of urine samples containing cortisol in variable concentrations. The proposed method was validated for specificity, linearity, LODs and LOQs, precision and trueness. The LOQ for cortisol equaled 5 ng/mL. The method was selective and reliable for identification and can detect changes of endogenous levels of cortisol in urine under different stress situations.

Spectrofluorimetric quantification of bromazepam using a highly selective optical probe based on Eu3+-bromazepam complex in pharmaceutical and serum samples

A rapid, simple and sensitive spectrofluorimetric method for determination of trace amount of bromazepam is developed. In phosphate buffer of pH 7.4. The bromazepam enhance the luminescence intensity of the Eu(3+) ion in Eu(3+)-bromazepam complex at lambda(ex)=390nm. The produced luminescence intensity of Eu(3+)-bromazepam complex is in proportion to the concentration of bromazepam. The working range for the determination of bromazepam is 2.3x10(-8) to 6.2x10(-7)M with detection limit (LoD) and quantitative detection limit (LoQ) of 3x10(-9) and 1.2x10(-8)M, respectively. While, the working range, detection limit (LoD) and quantitative detection limit (LoQ) in case of the quantum yield calculations are 3.7x10(-8) to 3.4x10(-7)M with of 3.4x10(-9) and 9.2x10(-8)M, respectively. The enhancement mechanism of the luminescence intensity in the Eu(3+)-bromazepam system has been also explained.

Prediction of micelle–water partition coefficient from the theoretical derived molecular descriptors

The micelle-water partition coefficients of 81 organic compounds in SDS solution were predicted by quantitative structure-property relationship method. The multiple linear regression (MLR) and artificial neural network (ANN) techniques were used to build linear and nonlinear model, respectively. In this work the proposed QSPR models, both by MLR and ANN, contain identical descriptors which are zero order of Kier-Hall index, count of Hydrogen donors site [Zefirovs PC], average valency of a C atom, atomic charge weighted by partial positively charged surface area and minimum one electron reaction index for a C atom. The MLR model gave a root mean square (RMS) of 0.166, 0.25, and 0.289 for training, prediction and test sets, respectively, whereas ANN gave an RMS error of 0.06, 0.21, and 0.20 for training, prediction, and test sets, respectively. Comparison the results of these two methods reveals that those obtained by the ANN model are much better.

Simultaneous determination of paracetamol, caffeine and propyphenazone in ternary mixtures by micellar electrokinetic capillary chromatography

A new micellar electrokinetic capillary chromatographic method has been developed to analyze the pharmaceutical preparations containing ternary combination of paracetamol (PAR), caffeine (CAF) and propyphenazone (PRO). Best results were obtained by using 20mM pH 9.0 borate buffer containing 30mM sodiumdodecylsulphate as the background electrolyte. Diflunisal (DIF) was used as internal standard (IS). The separation was performed through a fused silica capillary (50microm internal diameter, 44cm total length, 35.5cm effective length) at 25 degrees C with the application of 3s of hydrodynamic injection at 50mbar pressure and a potential of 29kV. Detection wavelength was 200nm. Under these conditions, the migration times were found to be 5.174min for PAR, 5.513min for CAF, 7.195min for DIF, and 9.366min for PRO. Linearity ranges for the method were determined as 2-200microgmL(-1) for PAR and CAF and 3-200microgmL(-1) for PRO. Limit of detections were found as 0.6microgmL(-1) for PAR and CAF and 0.8microgmL(-1) for PRO. According to the validation study, the developed method was proved to be accurate, precise, sensitive, specific, rugged and robust. Three pharmaceutical preparations, which are produced by different drug companies in Turkey, were analyzed by the developed method. One of the same preparations was also analyzed by the derivative ratio spectro zero-crossing spectrophotometric method reported in literature. No significant differences were found statistically.

Determination of selenium(IV) in pharmaceuticals and premixes by micellar liquid chromatography

A simple micellar liquid chromatographic technique for the determination of selenium(IV) in pharmaceutical products (multi-vitamin tablets, syrups) and animal premixes after pre-column derivatization with 2,3-diaminonaphthalene was developed and validated. Hypersil ODS column, 10% (v/v) 1-butanol in 0.05 M sodium dodecyl sulfate as the mobile phase and UV detection at 378 nm and were used. The retention time was about 8 min. In the course of the validation study, the specificity of the method was demonstrated. Linearity was established in the range 0.33-3.3 microg ml(-1) of selenium(IV) content. The limits of detection and quantitation were 0.1 and 0.3 microg ml(-1), respectively. The method showed excellent accuracy (100.04%). Precision (repeatability) gave a relative standard deviation less than 1%. The influence of the various method parameters (robustness study) was also investigated.

Surfactant gradient methods using mixed systems of cethyltrimethylammonium chloride and nonionic surfactants possessing polyoxyethylene chains for electrokinetic separation of benzoate anions as model analytes

Surfactant gradient methods for electrokinetic separation of 10 benzoates as model organic anions were investigated using mixed micellar solutions of cetyltrimethylammonium chloride (CTAC) and nonionic surfactants possessing polyoxyethylene chains, polyoxyethylene sorbitan monolaurate (Tween 20) or polyoxyethylene lauryl ether (Brij 35). Electroosmotic flow (EOF) was eliminated virtually by a coating of the inner wall of the capillaries, and then the benzoates were detected fundamentally in the order of their hydrophobicity. In a pure CTAC system, the synergistic influences of attractive electrostatic and hydrophobic interactions gave rise to quite large retention factors of many of the benzoate anions, resulting in their coelution. Addition of an adequate amount of Tween 20 to the pure CTAC system decreased the electrostatic interaction significantly to give remarkably improved separation of the analytes, but long analysis time was required. A surfactant gradient method would be useful to decrease analysis time and to improve separation simultaneously. Under slight EOF, the micelles in the inlet reservoir can pass through and, thus, interact with all of the analytes before they were detected. In the present system, surfactant gradient separations could be performed simply by changing compositions of the surfactant solutions in the inlet reservoir during a single run. Additionally, we carried out continuous gradient separation using a simple device. Brij 35 gave an effect parallel to that by Tween 20 in migration behavior of the analytes. A practically negligible change in the level of the baseline was observed in a stepwise gradient elution with the CTAC/Brij 35 system because of the small absorbance at the detection wavelength, while that with the CTAC/Tween 20 was considerable. All the benzoates were separated completely within reasonable analysis times using both stepwise and continuous gradient programs for the concentrations of Tween 20 or Brij 35 in the presence of 100 mM CTAC.

Heteroscedasticity of retention factor and adequate modeling in micellar liquid chromatography

The two concepts of micelle formation (pseudo-phase and mass-action) could be the basis of retention models in micellar liquid chromatography (MLC). The separation of 4-hydroxybenzoic acid esters and seven polyaromatic hydrocarbons were performed to study the repeatability of retention factor in MLC. The full two factor experimental design was used for studying the dependence of retention factor variance on mobile phase composition (sodium dodecylsulfate, 1-butanol). The experimentally observed heteroscedasticity and perturbations after linearization were taken into account by using statistical weights obtained on the basis of errors propagation law and the modeling of retention by non-weighted and weighted least squares method was performed. The mechanistical retention models based on pseudo-phase and mass-action concepts of micelle formation were compared by fitting quality and prediction capability and high robustness of bilogarithmic dependence was observed. The significance of retention factor heteroscedasticity for retention hydrophobicity relationships was shown.

Micellar liquid chromatography retention model based on mass-action concept of micelle formation

Mass-action model of surfactant micelle formation has been used to develop a conceptual retention model in micellar liquid chromatography (MLC). The retention model bases on the consideration of the changes of the sorbate microenvironment at its transferring from the mobile phase (hybrid micellar eluent) to the stationary phase (a modified surface of alkyl-bounded sorbent). Principal retention equation contains the characteristics of hybrid micelles (critical micelle concentration, degree of counterion binding, partition coefficient of modifier between aqueous solution and micellar pseudo-phase) as well as three fitting parameters. The fitting parameters are an absolute term and coefficients that are equal to the number of molecules of surfactant and modifier, which are attached/detached by sorbate transferring from a hybrid micellar eluent to a modified surface of the stationary phase. On the MLC separation of five antibiotics of rubomicin derivatives and four esters of 4-hydroxybenzoic acid the model of the change of sorbate microenvironment has been tested. The adequateness of model to experimental data has been shown. A simple three-parameter function connecting log k with log cS and log cR that provides a high goodness-of-fit follows from principal retention equation (cS and cR are the molar concentrations of surfactant and organic modifier in the micellar eluent, respectively).

Recent advances in microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) is an electrodriven separation technique. Separations are typically achieved using oil-in-water microemulsions, which are composed of nanometre-sized droplets of oil suspended in aqueous buffer. The oil droplets are coated in surfactant molecules and the system is stabilised by the addition of a short-chain alcohol cosurfactant. The novel use of water-in-oil microemulsions for MEEKC separations has also been investigated recently. This report summarises the different microemulsion types and compositions used to-date and their applications with a focus on recent papers (2002-2004). The effects of key operating variables (pH, surfactant, cosurfactant, oil phase, buffer, additives, temperature, organic modifier) and methodology techniques are described.

Electrokinetic capillary chromatography in a polar continuous-phase water-in-oil microemulsion constituted by water, sodium dodecyl sulfate, and n-pentanol

A water-in-oil (w/o) microemulsion (ME) constituted by 15% Tris buffer, pH 8.4, in water and 85% sodium dodecyl sulfate (SDS)/n-pentanol 1:4 mixture, capable of dissolving up to 30% vegetable oils and lard, was used as background electrolyte in reverse microemulsion electrokinetic capillary chromatography (RMEEKC). Owing to the free SDS ions in the continuous phase and some degree of percolation, the ME showed a high conductivity (0.65 mS. cm(-1) at 25 degrees C) and sustained a very stable capillary current. Previous rinsing of the capillary with a quaternary ammonium salt for electroosmotic flow (EOF) reduction, a series of nonionic and anionic solutes dissolved either in the ME or in fat samples diluted with the ME (1:4 ratio), were injected. Using -20 kV, fair separations of the solutes in the migration time order singly charged anions < nonionic solutes < doubly charged anions approximately pyromellitate were obtained, salicylate (I) showing by far the shortest migration time, and phthalate (II) and pyromellitate the longest. Separation was attributed to partition between the aqueous droplets, where pyromellitate and II were assumed to be trapped, and the n-pentanol continuous phase, where the mobilitites could be also modified by association of the solutes with SDS ions. Adequate EOF markers were not found, thus the relative mobility of any solute with respect to the mobility of the droplets, mu(r), was expressed as a fraction of the mobility of I with respect to that of the droplets, being mu(r) = (t(II) - t(R)) t(I) / [(t(II) - t(I)) t(R)], where t(R), t(I), and t(II) are the migration times of the solutes I and II, respectively. The application of RMEEKC to the analysis of both hydrophilic and hydrophobic samples, including edible fats, was demonstrated.

Analysis of antiepileptic drugs in biological fluids by means of electrokinetic chromatography

An overview of the electrokinetic chromatographic methods for the analysis of antiepileptic drug levels in biological samples is presented. In particular, micellar electrokinetic capillary chromatography is a very suitable method for the determination of these drugs, because it allows a rapid, selective, and accurate analysis. In addition to the electrokinetic chromatographic studies on the determination of antiepileptic drugs, some information regarding sample pretreatment will also be reported: this is a critical step when the analysis of biological fluids is concerned. The electrokinetic chromatographic methods for the determination of recent antiepileptic drugs (e.g., lamotrigine, levetiracetam) and classical anticonvulsants (e.g., carbamazepine, phenytoin, ethosuximide, valproic acid) will be discussed in depth, and their pharmacological profiles will be briefly described as well.

Chiral separations in microemulsion electrokinetic chromatography

In this study, microemulsions of the chiral surfactant polysodium N-undecenoyl-D-valinate (poly-D-SUV) was utilized for enantiomeric separation by investigating two approaches using polymeric chiral surfactant in microemulsion electrokinetic chromatography (MEEKC). In the first approach, poly-D-SUV was used as an emulsifier surfactant along with 1-butanol and n-heptane. Enantioseparation of anionic or partially anionic binaphthyl derivatives, anionic barbiturates, and cationic paveroline derivatives were achieved by varying the mass fraction of 1-butanol, n-heptane and poly-D-SUV. For anionic or partially anionic analytes, relatively lower mass fractions of n-heptane, and poly-D-SUV were found to give optimum chiral separations as compared to that for cationic solutes. In the second approach, the chiral microemulsion polymer was prepared by polymerizing mixtures of 3.50% (w/w) of sodium N-undecenoyl-D-valinate (D-SUV) and 0.82% (w/w) of n-heptane (core phase) at varying concentration of 1-butanol. After polymerization, the n-heptane and 1-butanol were removed to yield solvent free microemulsion polymers (MPs) which were then utilized for the separation of anionic binaphthyl derivatives and anionic barbiturates. When MPs of D-SUV were utilized for chiral separation, 1.00% (w/w) 1-butanol and 3.50% (w/w) 1-butanol was optimum for enantioseparation of (+/-)-BNP and (+/-)-BOH, respectively. On the other hand, for anionic (+/-)-barbiturates very low concentration of butanol (0.25%, w/w) provided optimum resolution. Compared with micellar electrokinetic chromatography (MEKC), the use of micelle polymers or microemulsion polymers in MEEKC showed dramatic enhancement for resolution of (+/-)-BNP, while this enhancement was less dramatic for other binaphthyls [(+/-)-BOH, (+/-)-BNA] as well as for (+/-)-barbiturates and (+/-)-paveroline derivatives. However, higher separation efficiency of the enantiomers was always observed with MEEKC than in MEKC.

Analysis of Ion-Association Reaction in Aqueous Solution and Its Utilization by Capillary Zone Electrophoresis

Electrophoretic migration of analytes in capillary zone electrophoresis (CZE) reflects the dissolved status of analytes in solution, and the electrophoretic mobility is controlled to develop the resolution among analytes by adding a "modifier" to the migrating solution. Such addition of modifier is essentially the utilization of molecular interactions. Precise measurement of electrophoretic mobility by CZE allows analyzing molecular interactions, and CZE apparatus is very useful for physicochemical measurements. This review focuses on the advantages on using CZE to analyze equilibrium reaction; the capillary electrophoretic method and mathematical analyses that apply acid dissociation and complex formation reactions are also validated. Ion association reactions are deeply related to analytical chemistry and separation science, and CZE has been used for the investigation of ion-ion interactions. Various types of interactions have been clarified through the CZE measurements: contributions of hydrophobicity, probability, and aromatic-aromatic interaction were quantitatively evaluated. Ion association reaction in aqueous solution also elucidates the stepwise reactions of liquid-liquid distribution of ion associates. Development and applications of ion association reaction in CZE analysis are also introduced.

Simultaneous micellar LC determination of lidocaine and tolperisone

A micellar liquid chromatography (MLC) procedure was developed for the simultaneous separation and determination of lidocaine hydrochloride (LD HCl) and tolperisone hydrochloride (TP HCl) using a short-column C18 (12.5 mm x 4.6 mm, 5 microm), sodium dodecyl sulfate (SDS) with a small amount of isopropanol, and diode array detector. The optimum conditions for the simultaneous determination of both drugs were 0.075 mol l(-1) SDS-7.5% (v/v) isopropanol with a flow rate of 0.7 ml min(-1) and detection at 210 nm. The LOD (2S/N) of LD HCl was 0.73 ng 20 microl(-1), whereas that of TP HCl was 1.43 ng 20 microl(-1). The calibration curves for LD HCl and TP HCl were linear over the ranges 0.125-500 microg ml(-1) (r(2)=0.9999) and 1.00-500 microg ml(-1) (r(2)=0.9997), respectively. The %recoveries of both drugs were in the range 98-103% and the %RSD values were less than 2. The proposed method has been successfully applied to the simultaneous determination of TP HCl and LD HCl in various pharmaceutical preparations.

Analysis of glycopeptide antibiotics using micellar electrokinetic chromatography and borate complexation

Micellar electrokinetic chromatography (MEKC) was investigated as a technique for the separation and analysis of the following related glycopeptide antibiotics: alpha-avoparcin, beta-avoparcin, ristocetin A, ristocetin B and vancomycin. Sodium dodecyl sulfate (SDS) micelles were employed as the pseudostationary phase in conjunction with borate or CHES buffers at pH 9.2. A complete separation of the glycopeptides was achieved only when two separation mechanisms were employed simultaneously: (i) differential partitioning of the glycopeptides into SDS micelles; and (ii) differential complexation of the glycopeptides with the borate anion from the borate buffer. Quantitatively, linearity was confirmed for each antibiotic from 0.5 to 40 ppm, with correlation coefficients (r(2)) ranging from 0.9996 (vancomycin and beta-avoparcin) to 0.9986 (alpha-avoparcin). Detection limits ranging from 0.01 ppm (vancomycin) to 0.2 ppm (avoparcin) were achieved, and the mean recovery of avoparcin at the 10 ppm level was 99.2%.

Systematic development and validation of stability indicating micellar electrokinetic chromatography methods for early stage drug candidates

Suitable methods for assessment of purity, potency and stability of new drug substances and drug products are required to be rapidly developed and validated to provide appropriate data for early project development decisions. In order to routinely provide methods of consistent and suitable quality to meet increasingly aggressive timelines, systematic approaches to both develop and validate analytical technologies have been developed. Systematic approaches to evaluate separation parameters such as buffer pH, buffer ionic strength, surfactant concentration, organic modifiers, organic modifier concentration, applied voltage and temperature were evaluated for an early stage drug candidate. Techniques to improve method precision and ruggedness were also examined. Finally, the validation results from the micellar electrokinetic chromatography method utilizing an internal standard were compared against the simultaneously developed high-performance liquid chromatography method.

Chemometric comparison of recent chromatographic and electrophoretic methods in a quantitative structure-retention and retention-activity relationship context

The retention characteristics of 21 basic pharmaceutical substances with a considerable difference in hydrophobicity (octanol-water partition coefficients, log P, between -0.026 and 6.45) are considered on an immobilized artificial membrane column, with a micellar liquid chromatography and a micellar electrokinetic capillary chromatography method. Utilising principal component analysis (PCA), it is seen that although the main retention principle is the same, the above methods as well as more classical RP-HPLC methods vary in secondary retention mechanisms. Combining the results of different methods a differentiation of the substances into their pharmacological families can be seen with PCA. The high correlations of the retention characteristics with log P and a biological parameter seem little affected by the method used.

Direct injection micellar liquid chromatographic determination of benzodiazepines in serum

A simple micellar liquid chromatographic (MLC) procedure is reported for the determination of several benzodiazepines in serum: bromazepam, diazepam, flunitrazepam, halazepam, medazepam, nitrazepam, oxazepam and tetrazepam. The optimization studies have been made in C(18) and C(8) columns, using solutions containing sodium dodecyl sulphate (SDS) modified with butanol or pentanol as mobile phases. The method proposed for the determination of the benzodiazepines uses a hybrid micellar mobile phase of 0.06 M SDS-5% butanol-0.01 M phosphate buffer (pH 7) at 25 degrees C, and UV detection (230 nm) in a C(18) column. The serum samples were injected directly, without any pretreatment, and eluted in less than 22 min, in accordance with their relative polarities, as indicated by their octanol-water partition coefficients. The limits of detection (ng ml(-1)) were within the ranges of 2-6 and 4-18 for aqueous and serum samples, respectively. Repeatability and intermediate precision were tested for three different concentrations of the drugs, and RSD (%) was below 10 for most of the assays. The MLC results were compared with those obtained from a conventional HPLC method using methanol-water 5:5 (v/v) which requires a previous extraction procedure.