Analysis of clindamycin by micellar electrokinetic chromatography with a mixed micellar system.

This study details the development and validation of an optimized method with micellar electrokinetic chromatography for the analysis of clindamycin. The method uses a mixed micellar phase containing anionic sodium dodecylsulfate (SDS) and non ionic Brij 35 on an untreated fused-silica capillary. The influences of buffer concentration, pH, SDS, Brij 35 and organic modifier were investigated. Special attention was given to the role of the non ionic Brij 35 in the mixed micellar system. Optimization with a central composite design resulted in optimal separation conditions: background electrolyte containing 25 mM sodium tetraborate pH 7.75, 90 mM SDS, 14 mM Brij 35 and 21% acetonitrile. The applied voltage was 15 kV and the capillary temperature 15 degrees C. The method was robust and gave good linearity and repeatability. The limits of detection and quantitation were 0.05 and 0.15%, respectively, relative to a 2.5 mg/ml clindamycin solution. Two commercial bulk products were analysed with this system.     

Comparative study of capillary zone electrophoresis and micellar electrokinetic chromatography for the separation of twelve aromatic sulphonate compounds

Summary Two modes of capillary electrophoresis (CE), capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC), were investigated for the separation of 12 aromatic sulphonate compounds. In CZE, although the voltage applied, the buffer concentration and the pH were optimized for effective separation of the compounds studied, under the best conditions four of the five amino compounds coeluted, as did naphthalene-1-sulphonic acid and naphthalene-2-sulphonic acid. In MEKC, sodium dodecyl sulphate (SDS) and Brij 35 were chosen as the anionic and nonionic surfactants and the effect of the concentration of micelles was examined. The effect of adding methanol as the organic modifier was also investigated with each of these micellar systems. All the analytes, including the isomers, were completely separated by use of MEKC with Brij 35 but when SDS was used only 11 compounds were separated because two amino compounds coeluted.     

Optimization of separation and migration behavior of chloropyridines in micellar electrokinetic chromatography

The separation and migration behavior of pyridine and eight chloropyridines, including three monochloropyridines, four dichloropyridines, and 2,3,5-trichloropyridine were investigated by micellar electrokinetic chromatography using either sodium dodecyl sulfate (SDS) as an anionic surfactant or SDS-Brij 35 mixed micelles. Various parameters such as buffer pH, SDS concentration, Brij 35 concentration and methanol content that affect the separation were optimized. Complete separation of these chloropyridines was optimally achieved with a phosphate buffer containing SDS (30 mM) and methanol (10%, v/v) at pH 7.0. The resolution and selectivity of analytes could be considerably affected by the addition of methanol and/or Brij 35 to the background electrolyte. The migration order of these chloropyridines depends primarily on their hydrophobicity. However, electrostatic interactions may also play a significant role in the determination of the migration order of the positional isomers of chloropyridines.     

THE EFFECTS OF MIXED MICELLES OF SURFACTANTS ON POLYMERIZATION OF ACRYLAMIDE

The polymerization of acrylamide in mixed micellar solutions of surfactants, initiated by NaHSO₃ has been studied at 20 and 3Q° C with time variable method of thermokinetics for 1. 5-order reaction. The results indicate that the mixed micellar systems of cationic or anionic with zwitterionic surfactants (SLS/ CTAB, SLS/ TTAB, SLS/ SDS) and cationic with nonionic surfactants (Brij 357sol; CTAB, Bri-J35/TTAB, Brij35/ DTAB) have catalytic effect on the polymerization in the order, at 20° C. SLS/ SDS SLS/ TTAB SLS/ CTAB Brij35/ CTAB at 30° C SLS/ SDS SLS/ TTAB≈ / CTAB Bri-j35/ DTAB= sBrij35/ TTAB as Brij35/ CTAB, while Brij35/ SDS mixed micellar system has inhibition. These effects are attributed to the effect of the Stern layer of mixed micelles on the step of initiator (HSOT) to form free radical.     

Separation and mechanism elucidation for six structure-like matrine-type alkaloids by micellar liquid chromatography

A mixed micellar liquid chromatography (MLC) method, the mobile phase consisting of anionic surfactant SDS and nonionic surfactant Brij35, was firstly developed for the separation and determination of six structure-like matrine-type alkaloids, including matrine, oxymatrine, sophocarpine, oxysophocarpine, sophoridine, and oxysophoridine. The factors influencing the resolution of the six alkaloids were systematically investigated and optimized, including the micellar composition and concentration, column temperature, the type and amount of organic solvent, and the pH values in the mobile phases. Under the optimized separation conditions, the six matrine-type alkaloids could be easily isocratically eluted with a baseline separation within 22 min. Under the designated conditions (SDS concentration from 10 to 50 mM, Brij35 from 5 to 30 mM, pH 3 and 5% 1-propanol), the hydrophobic selectivity was negatively correlated with the concentration of Brij35 but not with SDS. The functional group selectivity of the carbonyl group, double bond, and diastereomers, all decreased with the increase in percentage of SDS in the mixed micellar phase, because the strong electrostatic force masks other molecular forces which can discriminate the retention of the analytes. Therefore, such a combination in surfactants of MLC is a powerful strategy to increase the selectivity by adjusting the balance among the various molecular interaction forces influencing analytes' retention. Finally, the developed method was successfully used to separate and determine the contents of main alkaloids in Sophora medicinal plants, S. flavescens Ait. In summary, the mixed MLC is a valuable approach to separate and determine the structure-like multi-component natural samples.     

Solubilization of Aliphatic Carboxylic Acids (C3-C6) by Sodium Dodecyl Sulfate and Brij 35 Micellar Pseudophases

The apparent dissociation constants of 1-propanoic, 1-butanoic, 1-pentanoic and 1-hexanoic acids were obtained for the first time in Brij 35 micellar solutions with concentration from 0.03 to 0.20 mol⋅L⁻¹ and sodium dodecyl sulfate (SDS) micellar solutions with concentrations from 0.01 to 0.30 mol⋅L⁻¹. A pronounced effect of Brij 35 micelles on the acid-base properties of aliphatic acids was observed. The binding constants, K _b, of carboxylic acids to micellar pseudophases of SDS and Brij 35 were estimated within the framework of the pseudophase model. The dependences of Gibbs energies of transfer from water to the micellar pseudophases were constructed, and Gibbs energies were evaluated for methylene and carboxylic group transfers into Brij 35 and SDS micelles. Comparison of the Gibbs energies of methylene group transfer from water to Brij 35 and SDS suggests that the mechanisms of hydrocarbon group transfer into the core of nonionic and anionic micelles involving the same monomer hydrophobic tail length are similar.     

Development of predictive quantitative retention–activity relationship models of alkaloids by mixed micellar liquid chromatography

The mixed micellar liquid chromatography is a mode that uses mixed micellar system of Brij35/SDS (85 : 15) as a mobile phase under adequate experimental conditions, can simulate the resting membrane potential and the conformation of the long hydrophilic polyoxyethylene chains remains unchanged. In this article, the applications of biopartitioning micellar chromatography, using mixed micellar system to describe and estimate bioactivities of alkaloids, has been focused. The BMC_Brij35/SDS‐QRAR models of half‐life time, volume of distribution, plasma clearance and area under concentration–time curve were obtained using Brij35‐SDS retention data. The aim is to take a look at the capability of the mixed micellar liquid chromatography model to describe and/or estimate the bioactivity of alkaloids. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimization of resolution in micellar electrokinetic chromatography

A comparison of separations conducted in sodium dodecyl sulfate (SDS) and SDS modified with Brij 35 indicates that selectivity, in Micellar Electrokinetic Chromatography (MEKC), is governed by the composition of the micellar phase. Beyond selectivity optimization, resolution may be improved by increasing efficiency or decreasing electroosmotic flow. Of these approaches, increasing capillary length (to improve efficiency) should be a more time effective means of improving separation.     

THE EFFECT OF MIXED MICELLES OF SURFACTANTS ON THE ALKALINE HYDROLYSIS OF ESTERS

The alkaline hydrolysis of aromatic and normal aliphatic acid esters have been studied at 25°C In mixed micellar solution of surfactants (Brij35—SDS, Brij35 — DTAB, Brij35—TTAB.Brij35-CTAB. Triton X—100 —CTAB, Triton X— 100 —SDS) with UV spectrophotometry and the method of thermokinetics The critical mice liar concentrations of the corresponding systems have also been measured with UV spectrophotometry in this paper. K_jnln micellar pseudo-phase has been calculated- The ratios of ki.to ki.for all mixed micellar systems Investigated are less than 1. The results indicate that these reactions are inhibited by the mixed micelles and the mixed micelles exhibit a greater effect of Inhibition on the reactions than those do In corresponding single ones. The reason for this is that the micropolarity of the compact Stern layer of mixed micelle is lower, and the micro viscidity Is higher. The Inhibition effect! also depend on the hydrophobic chain length of the surfactants and the hydrophobicity of the substrate.     

Determination of vitamins A and E in milk samples by fluorescence in micellar media

The fat-soluble vitamins A and E in milk samples were determined by fluorescence at room temperature in an aqueous media of micellar solutions. Different types of surfactants were studied; the cationic hexadecyltrimethylammonium bromide (CTAB), the anionic sodium dodecylsulfate (SDS) and the non-ionic polyoxyethylene(23)laurylether (Brij 35). The detection limits ranged between 50 and 90 ng.L-1 for both vitamins in CTAB and Brij 35. The method has been applied to the determination of vitamins A and E in milk samples.     

Systematic investigations of different capillary electrophoretic techniques for separation of methylquinolines

The migration behaviour of isoquinoline, quinoline, and methyl derivatives of quinoline in different capillary electrophoretic modes has been systematically investigated. Optimised separation conditions were established by varying the key parameters (solvent, pH, temperature, surfactant concentration, core phase) for aqueous and non‐aqueous capillary zone electrophoresis (NACE), micellar electrokinetic chromatography (MEKC) with anionic or non‐ionic micelles (SDS, Brij 35), and microemulsion electrokinetic chromatography (MEEKC) with charged or uncharged microemulsion droplets. A separation of all quinolines could be achieved by MEEKC with charged droplets, by MEKC or by formamide‐based NACE. Comparing the separations with respect to separation selectivity, substantial changes in migration order could be observed between the different techniques. Regarding separation efficiency, the number of theoretical plates and limits of detection (LOD) have been compared. The best LODs were achieved using SDS as surfactant in MEKC, followed by MEEKC.     

Comparative study of capillary zone electrophoresis and micellar electrokinetic capillary chromatography for the separation of naphthalenedisulfonate isomers

We investigated the separation of a test mixture of nine substituted and unsubstituted naphthalenedisulfonate isomers by capillary electrophoresis with a UV diode array detector. In particular, we focused on how the composition of the running buffer affected the separation selectivity. When capillary zone electrophoresis was carried out, the best results were obtained when organic solvents such as ethanol or propan-2-ol were added. Eight peaks were baseline separated but in no case were all the unsubstituted isomers separated. Therefore, capillary electrophoretic separation of the compounds was examined in the presence of micellar agents, such as sodium dodecyl sulfate, polyethylene glycol dodecyl ether (Brij 35) and cetyltrimethylammonium bromide. All the substituted isomers and two of the unsubstituted isomers were well resolved within 20 min by micellar electrokinetic capillary chromatography when Brij 35 was used as micellar agent. Separations were reproducible, in terms of peak area and migration time, under these conditions.     

ENERGY TRANSFER IN TRITON X-405 MICELLES: THE EFFECTS OF TEMPERATURE AND BRIJ 35

–Energy transfer from the phenyl groups of micellar Triton X-405 (TX-405) to solubilized pyrene molecules has been measured at a range of temperatures and in the presence of different polyoxyethylene 23 lauryl ether (Brij 35) concentrations. Increases in temperature lead to elimination of water from the outer, wet, micelle layer and an inward movement of associated pyrene. The addition of Brij also leads to a reduction in polarity of the microenvironment of pyrene. However, sensitization is observed even at high Brij concentrations. The donor/acceptor separation caused by the introduction of Brij proceeds slowly, continuing for several minutes after its addition to micellar TX-405.     

Mixed micellar liquid chromatography methods: modelling quantitative retention-activity relationships of angiotensin converting enzyme inhibitors

The capability of biopartitioning micellar chromatography (BMC), using pure Brij35 solution and mixed micellar system of Brij35-SDS (85:15) as mobile phase, to describe and estimate bioactivities of angiotensin converting enzyme inhibitors at different pH has been studied. Quantitative retention-activity relationships (QRAR) in BMC were investigated for these compounds. The obtained BMC(Brij35-SDS)-QRAR models were compared with the traditional BMC(Brij35)-QRAR, and better statistically models were obtained using Brij35-SDS retention data. The superiority of BMC(Brij35-SDS)-QRAR is due to the fact that the mixed micellar mobile phase can simulate the resting membrane potential and the conformation of the long hydrophilic polyoxyethylene chains remains unchanged.     

Spectrophotometric Determination of Acidity Constants of 4‐(2‐Pyridylazo) Resorcinol in Various Micellar Media Solutions

Dissociation equilibria of 4‐(2‐pyridylazo) resorcinol (PAR) in aqueous micellar solutions were determined spectrophotometrically at 25 °C and at the constant ionic strength I = 0.1 M KNO₃. For this purpose, the effect of nonionic (Brij‐35, Triton X‐100, Triton X‐114, Triton X‐405), and anionic (SDS) surfactants on the absorption spectra of PAR at different pH values was studied. Results show that the pK_a values and pure spectra of each species of PAR are influenced by percentages of a neutral and an anionic surfactant such as Brij‐35, Triton X‐100, Triton X‐114, Triton X‐405 and SDS, respectively, added to the solution of this reagent.     

Determination of vitamins A and E in milk samples by fluorescence in micellar media

The fat-soluble vitamins A and E in milk samples were determined by fluorescence at room temperature in an aqueous media of micellar solutions. Different types of surfactants were studied; the cationic hexadecyltrimethylammonium bromide (CTAB), the anionic sodium dodecylsulfate (SDS) and the non-ionic polyoxyethylene(23)laurylether (Brij 35). The detection limits ranged between 50 and 90 ng · L^–1 for both vitamins in CTAB and Brij 35. The method has been applied to the determination of vitamins A and E in milk samples. Received: 30 June 2000 / Revised: 13 September 2000 / Accepted: 16 September 2000     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

Interaction of surfactants with thickeners used in waterborne paints: a rheological study

Studies of the phase diagram and linear viscoelasticity of aqueous solutions of hydrophobically modified hydroxyethyl cellulose (HMHEC), a thickener used in water-based paints, and SDS reveal that SDS-HMHEC mixed micelles are formed that increase the number of hydrophobic junctions and enhance interpolymer association up to an [SDS]/[HMHEC] ratio. This fact produces a strong increase of viscoelasticity or a phase separation, depending on the [HMHEC]. At higher ratios the excess of micelles with predominant SDS isolates hydrophobes and disrupts the micellar network. Then, viscoelastic functions decrease and HMHEC behaves as a nonassociative polymer. TTAB and Brij30 also interact with HMHEC, but in a different way. No phase separation is observed with these surfactants. TTAB forms mixed micelles and new junction points in the same way as SDS. However, this surfactant does not stabilize the micelles as SDS does, presumably due to the different interaction between the OH from the cellulose and the charged groups. Results seem to indicate that Brij30 enters into the hydrophobic aggregates of HMHEC and stabilizes them, increasing relaxation time, but it does not form new junction points, since it forms quite big micelles.     

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.     

Simultaneous determination of antioxidants, preservatives and sweeteners permitted as additives in food by mixed micellar electrokinetic chromatography.

A micellar electrokinetic chromatography method was developed to simultaneously analyse commonly used food additives. The additive mixture, comprising propyl gallate, octyl gallate, dodecyl gallate, butylated hydroxyanisole, butylated hydroxytoluene, tertiary butylhydroquinone, p-hydroxybenzoic acid methyl ester, p-hydroxybenzoic acid ethyl ester, benzoic acid, sorbic acid, saccharin, aspartame and acesulfame-K, was not resolved using single surfactant micellar systems consisting of sodium dodecyl sulfate (SDS), sodium cholate (SC) or sodium deoxycholate (SDC). The separation of these additives using mixed micellar systems, involving SDS/SC, SDS/SDC and SC/SDC, was investigated. Organic solvents were added to the mixed micellar phases to optimise the separation. The mixture was successfully separated using a 20 mM borate buffer with 35 mM SC, 15 mM SDS and 10% methanol added at pH 9.3. Additives in cola beverages and low-joule jam were investigated and quantified using this method.