Micellar electrokinetic capillary chromatography of nucleic acid constituents and dinucleoside monophosphate photoproducts

Micellar electrokinetic capillary chromatography has been explored as an efficient and rapid method of separating the photoproducts of 2′-deoxyuridylyl-(3′-5′)-thymidine (i.e., cis-syn and trans-syn cyclobutane dimers, (6–4) photoproduct, and the related Dewar valence isomer) from normal nucleosides and nucleotides. Three cationic surfactants, dodecyl-, tetradecyl-, and hexadecyltrimethy-lammonium bromide were evaluated and the separations compared with those obtainable with the anionic surfactant, sodium dodecylsulfate. Optimum resolution of the dinucleoside monophosphate photoproducts was obtained using tetradecyltrimethylammonium bromide. By use of this detergent the photoproducts could also be separated from other normal constituents in less than 6 min at ?25 kV. Dodecyl- and hexadecyltrimethylammonium bromide provided some separation between the various species but sodium dodecylsulfate did not separate the UV radiation-induced products from either the parent compound or other dinucleoside monophosphates. Increased interaction between negatively charged solutes and positively charged micelles accounts for the differences.     

Separation of anabolic steroids by micellar electrokinetic capillary chromatography

Summary The separation of seven analogous anabolic steroids was studied by micellar electrokinetic capillary chromatography (MECC). The retention order was found to be dependent on polarity. All of these steroids were well separated by the addition of organic modifiers to the separation buffer. Of the organic modifiers tested, 1-propanol gave the best separation, better than methanol or acetonitrile.     

Determination of doxycycline in pharmaceuticals and human urine by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MEKC) was performed at 25 °C and 30 kV (under a pressure of 15 mbar), using 30 mM borate buffer containing 60 mM sodium dodecysulfate (SDS) and 5% (v/v) methanol as background electrolyte (pH 9.0) to determine doxycycline. UV detection was at 350 nm. The method was shown to be specific, accurate (recovery was 100.3 ± 1.0%), linear over the tested range (correlation coefficient 0.9995) and precise (RSD <1.9%). The method was used to determine doxycycline in tablets, capsules and human urine after oral application.     

Pesticide analysis by micellar electrokinetic capillary chromatography

On-capillary sample concentration using sample stacking for the improvement of detection limits for various pesticides separated by micellar electrokinetic capillary chromatography was examined. The dependence of the stacking on different parameters was investigated. An approximately 30-fold preconcentration was achieved by applying sample stacking. Employing a two-step enrichment process (solid-phase extraction combined with sample stacking), detection limits were improved and the sample volume for SPE was reduced. In addition, the total time for the analysis was considerably reduced. Detection limits were between 0.01 and 0.1 ng/ml under these enrichment conditions.     

Micellar electrokinetic capillary chromatography using polymeric hollow fibers

Summary In this paper, polymeric hollow fibers prepared from pH-stable polypropylene were used as columns for micellar electrokinetic capillary chromatography (MECC). The electroosmotic flow (EOF) for polypropylene hollow fibers was evaluated in the pH range of 5.0–12.0. With untreated polypropylene hollow fibers a stabilized but enhanced EOF was achieved when SDS was used in the buffer, decreasing the separation window for uncharged substances in MECC to impractical levels. Uncharged acrylamide and charged 2-acryloylamido-2-methylpropane sulfonic acid surface modifications were used to lower the strength of the EOF, increase the separation window and prevent local overheating that could melt the column wall.     

Study of urinary nucleosides as biological marker in cancer patients analyzed by micellar electrokinetic capillary chromatography

Thirteen normal and modified nucleosides, primarily degradation products of transfer ribonucleic acid (tRNA), were evaluated as potential tumor markers for cancer patients. Their urinary concentrations were determined by means of micellar electrokinetic capillary chromatography (MEKC) in the urine from 54 healthy adults and 70 cancer patients, then quantitatively expressed as a function of creatinine excretion. It was found that urinary nucleosides for cancer patients were on the average significantly higher than those for healthy controls, however, no significant differences were found between male and female or between different ages. Based on 13 urinary nucleoside concentrations, principal component analysis (PCA) could be used to classify 72% of cancer patients from the healthy controls. The present study shows that the precise measurement of urinary nucleosides by MEKC in combining with PCA technique may provide a clinically useful approach for diagnosis of cancer.     

Analysis of neutral and sialylatedN-liked oligosaccharides by micellar electrokinetic capillary chromatography with addition of a divalent cation

Summary Micellar electrokinetic capillary chromatography (MECC) has been investigated as an alternative mode of analyzing oligosaccharides released from glycoproteins. The influence on the separation of experimental parameters such as the concentrations of surfactant and electrolyte and the addition of divalent cations was examined. Solubilization, of neutral oligosaccharides by micelles was demonstrated whereas for the sialylated oligosaccharides the electrophoretic mobility remained the predominant factor. The addition of Mg⁺⁺ to sodium dodecyl sulfate (SDS)solutions provided an effective means of enhancing the selectivioty of the separation through both an increase of the time window and the differential complexation of carbohydrate with this divalent cation.     

Optimization strategies in micellar electrokinetic capillary chromatography

Summary Computer-assisted procedures for the one-parameter optimization of the surfactant concentration and the concentration of urea or D-glucose as modifiers in micellar electrokinetic capillary chromatography have been developed. These procedures permit a rapid optimization of one parameter on the basis of only two experiments. Predicted values are compared to empirically obtained optimum values. The influence of the modifier concentration on the critical micelle concentration of sodium dodecyl sulfate was experimentally determined in buffers commonly employed in micellar electrokinetic chromatography. The alteration of retention factors of solutes caused by the influence of urea addition on the critical micelle concentration of sodium dodecyl sulfate was calculated under the assumption of constant distribution coefficients and compared to experimentally obtained values. It was demonstrated that the addition of urea or of D-glucose does not alter the phase ratio substantially.     

Direct multicomponent analysis of beer samples constituents using micellar electrokinetic capillary chromatography

A capillary electrophoretic method was developed using micellar electrokinetic capillary chromatography (MEKC) with diode-array detection to analyze simultaneously 26 beer constituents in a single procedure, including alcohols, iso-alpha-acids, amino acids, flavonoids, isoflavonoids, a vitamin, purine and pyrimidine bases. After filtration, sample components were separated with an uncoated capillary and a 25 mM sodium borate and 110 mM SDS buffer at pH 10.5. Analyses were run at 14 kV and 8 s of hydrodynamic injection with UV detection at 210 nm and 270 nm. The proposed method was successfully applied to the direct determination of beer constituents without any sample cleanup procedures.     

Profiling propolis flavonoids by means of micellar electrokinetic capillary chromatography, capillary gas chromatography and bactericidal action

Summary There is no proportional correlation between increasing organic solvent polarity from hexane to methanol and the extractability of propolis solids by the solvents or the bactericidal action of the propolis extracts obtained. Hexane (17.7%) and chloroform (62.1%) were the poorest and the best extractants, respectively, for propolis solids. The antibiotic activity of the extracts againstStaphylococcus strains decreased in the order hexane≥ethanol>methanol. Different capillary GC profiles were obtained for persilyl derivatives of propolis extracted with hexane and methanol and for propolis collected in different Brazilian provinces, suggesting the influence of flora variability on propolis composition. Wavelength-selected DAD detection revealed MEKC to be an innovative and sensitive method for monitoring the occurrence in propolis of the flavonoids and phenolcarboxylic acids thought to be responsible for the antimicrobial activity of propolis.     

Micellar electrokinetic capillary chromatography of algal toxins

Recent methods employed for the analysis of algal toxins have focused on high performance liquid chromatography. However these methods suffer from poor resolution, poor efficiency, and long analysis times. This study involves the investigation of a number of toxins including nodularin, microcystin LR, YR, and RR which are cyclic peptides produced by strains of blue-green algae. The electroseparation mode was micellar electrokinetic capillary chromatography (MECC) using a borate buffer containing sodium dodecyl sulfate (SDS) as the surgactant of choice. The method was optimized with standard toxin compounds and employed for the screening opf toxins in supercritical fluid extracts (SFE) of freeze-thawed algal scum samples.     

胶束电动毛细管色谱法测定植物中的水杨酸

建立了以胶束电动色谱为分离模式测定植物中水杨酸的新方法。在一定范围内，随着硼酸和甲醇浓度的升高，苯甲酸内标和水杨酸的分离度以近似线性关系升高；随缓冲液pH的升高分离度呈非线性升高；随十六烷基三甲基溴化铵浓度的升高分离度呈非线性下降。在优化的条件下，两可在12min内分离。测定了苹果和梨样品，并做了回收率试验，回收率在97.1%-102%之间。     

Optimization strategies in micellar electrokinetic capillary chromatography. Optimization of the temperature of the separation capillary

Summary The influence of the temperature of the capillary on the separation of small molecules by micellar electrokinetic chromatography with buffers containing sodium dodecyl sulfate was examined. Investigated parameters were the electroosmotic velocity, the migration velocity of the micelles, the strength of the electric current, retention factors and plate numbers. Thermodynamic parameters associated with micelle solubilization were evaluated from the variation of the retention factor with temperature. An investigation was carried out as to whether the dependence of the electroosmotic velocity and the migration velocity of the micelles are mainly due to the decrease in viscosity and dielectric constant with increase in temperature. The temperature of the capillary strongly affects the plate numbers for various solutes obtained with the same chromatographic system. In order to exclude secondary effects by alteration of the instrumental band broadening and the electroosmotic velocity with temperature, a method is presented that permits the development of chromatograms in MEKC at various temperatures with constant injected plug length and constant electroosmotic velocity. The results are discussed from the point of view of minimizing the analysis time and optimizing the resolution.     

Determination of orotic acid in aqueous solutions by micellar electrokinetic capillary chromatography using sensitized lanthanide-ion luminescence detection

Summary A sensitive and selective laser-induced luminescence detection scheme for orotic acid in urine, separated by micellar electrokinetic capillary chromatography (MEKC) has been developed. The 325 nm line from a helium cadmium laser is used to excite orotic acid, which transfers its energy to terbium. Resultant luminescence of terbium is linear with orotic acid concentration over more than 2.5 orders of magnitude. This novel and practical system enables the detection of 50 nm orotic acid in urine in less than 1.5 minutes while using only nanoliters of sample. The significant decrease in analysis time over traditional methods (spectrophotometric and chromatographic) comes from the high efficiency of MEKC. A dramatic improvement in sensitivity and selectivity over UV detection in capillary electrophoresis is achieved through the use of laser-induced lanthanide ion energy transfer luminescence detection. Finally, no sample pretreatment is needed and the method is free from any known interferences in urine.     

Determination of phenolic whitening agents in cosmetics by micellar electrokinetic capillary chromatography with amperometric detection

A sensitive method for simultaneous determination of six phenolic whitening agents,including arbutin, phenol,resorcinol,hydroquinone,kojic acid,and salicylic acid in cosmetics has been developed using micellar electrokinetic capillary chromatography with amperometric detection（MECC-AD）.Effects of several factors,such as the pH value and concentration of running buffer,potential applied to the working electrode,separation voltage,and injection time were investigated to obtain optimum conditions for separation and detection.With a 75 cm long fused-silica capillary tube,well-defined separation of six phenolic compounds was achieved in 10mmol/L SDS/40 mmol/L H₃BO₃-Na₂B₄O₇ running buffer（pH 9.0）.Good linear relationship was obtained for each analyte over three orders of magnitude with correlation coefficients（r2） between 0.9985 and 0.9994,and the detection limit（S/N=3） ranged from 0.04μg/mL to 0.45μg/mL The proposed method has been successfully applied for the determination of phenolic whitening agents in real cosmetic samples with satisfactory results,providing an alternative monitoring method for cosmetics safety regulation.