Determination of urinary hippuric acid by micellar electrokinetic capillary chromatography

We propose a method for the simultaneous determination of hippuric acid (HA) and creatinine based on capillary micellar electrokinetic chromatography. Experimental conditions were 20 mM sodium phosphate, pH 7.20, 25 mM sodium dodecyl sulfate, 5% (v/v) acetonitrile. Electropherograms evidenced HA and creatinine peaks in less than 12 min. The method showed good linearity for both analytes and satisfactory within-day precision. The present method, which is accurate, sensitive, rapid and simple, may be applied to single-spot urine samples.     

Determination of alginate copolymer in pharmaceutical formulations by micellar electrokinetic chromatography

A micellar electrokinetic chromatography method was developed for the determination and quantification of sodium alginate. The alginate peak migrated in the very short time of 1.33 min and calibrated easily though the polydisperse properties of alginates. The minimum detection limit (LOD) of the method was calculated as 0.393 mg/ml. This analysis method was successfully applied to the alginate quantification in an antacid pharmaceutical formulation. Precise and reproducible analysis results were obtained, with liquid formulations injected directly without any pre-separation process.     

Determination of thiamphenicol in human plasma by micellar electrokinetic capillary chromatography

A micellar electrokinetic chromatographic method is described for the determination of thiamphenicol in human plasma. The plasma sample was basified by adding K₂HPO₄ and was then extracted with ethyl acetate. After the solvent was evaporated, the residue was reconstituted in water. Approximately 40 nl of the solution were injected hydrodynamically. The running buffer was 20 mM borate (pH 9.2) containing 40 mM sodium dodecyl sulfate and 10% acetonitrile. The applied voltage was 18 kV and the detector wavelength was set at 195 nm. On-column sample stacking was achieved during the analysis to enhance the sensitivity; the limit of quantitation was 0.1 μg/ml. Linearity was over the range of 0.2 to 10 μg/ml. Recovery was 93.7±3.3%, the intra-day precision and accuracy was 99.6±2.8%; the inter-day precision and accuracy was 98.4±3.4%. The concentration of thiamphenicol in human plasma from eight volunteers was measured after administering thiamphenicol capsules orally.     

Determination of aucubin and catalpol in Plantago species by micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC) was used for the separation and determination of two iridoid glycosides, aucubin and catalpol, in several Plantago species growing in Croatia: P. altissima L., P. argentea Chaix, P. coronopus L., P. holosteum Scop. (subsp. depauperata, subsp. holosteum and subsp. scopulorum), P. lagopus L., P. lanceolata L., and P. maritima L. Hot water extraction (HWE) was applied for the isolation of iridoid substances. Significant differences appeared between the iridoid contents in the examined species. The yield of aucubin and catalpol was up to 0.27% and 1.81% of the dry mass of the leaves, respectively. Besides aucubin and catalpol, two related compounds were determined in the plant samples.     

Determination of diterpenoid triepoxides in Tripterygium wilfordii by micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary chromatographic (MEKC) method has been established for the identification and determination of diterpenoid triepoxides in the Chinese herb Tripterygium wilfordii Hook F. and its preparations. Studies of the influence of boric acid and borax buffer concentration and pH, and of sodium dodecylsulphate (SDS) concentration have been carried out, and the optimum separation for the triepoxides was achieved using 20 mM boric acid and 10 mM borax with 20 mM SDS as the running buffer. MEKC was found to exhibit good accuracy, precision and repeatability. The sensitivity of the assay was sufficient to monitor the three active components in T. wilfordii and its preparations.     

Separation of bisbenzylisoquinoline alkaloids by micellar electrokinetic chromatography

The micellar electrokinetic chromatographic (MEKC) separation of seven bisbenzylisoquinoline alkaloids has been developed. The effects of various separating factors were studied. Optimum separation was achieved using a buffer (pH 9.2) of 20 mM sodium borate and 20 mM sodium dihydrogen phosphate buffer containing 55 mM sodium cholate; the optimum voltage and injection time were 21 kV and 0.05 min, respectively. Highest peak efficiency was obtained when the analytes were dissolved in 10 mM sodium dodecyl sulphate as sample matrix for injection. The elution order of the bisbenzylisoquinoline alkaloids was related to their lipophilicity. The resolution, run time and detection limits of the MEKC method were compared with those of an HPLC method developed previously.     

Determination of 1-phenyl-3-methyl-5-pyrazolone-labeled carbohydrates by liquid chromatography and micellar electrokinetic chromatography

In this paper, the method for the derivatization of carbohydrates with 1-phenyl-3-methyl-5-pyrazolone (PMP) was simplified. One-third of the derivatization time was saved. Five monosaccharide derivatives have been well separated by MEKC and HPLC under optimized conditions. Good reproducibility could be obtained with relative standard deviation (RSD) values of the migration times within 5.0 and 2.3%, respectively. Furthermore, the developed methods have been successfully applied to the analysis of carbohydrates in Aloe powder and food. These methods are quite useful for routine analysis of monosaccharides and oligosaccharides in real samples.     

Determination of corticosterone in mouse plasma by a sweeping technique using micellar electrokinetic chromatography

The separation and on-line concentration of corticosterone in mouse blood was achieved by means of capillary electrophoresis/UV absorbance using sodium dodecyl sulfate (SDS) as a surfactant. The procedure involved the use of an on-line sample concentration method by sweeping-micellar electrokinetic chromatography (sweeping-MEKC). Optimal on-line concentration and separation conditions were determined. The detection limit for this method was 5 ng/ml (S/N=3) and photodiode array detection at 247 nm was used for identification. For the analysis of actual samples, corticosterones from blood samples of a non-stressed and stressed mouse were determined. The results show that only a minor amount of corticosterone was produced by a non-stressed mouse, whereas a significant amount was present in the blood sample from a stressed mouse. The method developed here can be used to examine corticosterone levels as a marker of stress in test animals and may also be used for estimating the effect of stress-release medications.     

Analysis of creatinine, vanilmandelic acid, homovanillic acid and uric acid in urine by micellar electrokinetic chromatography

A simultaneous determination of vanilmandelic acid, homovanillic acid, creatinine and uric acid using capillary electrophoresis was investigated. The optimum conditions of buffer concentration, pH and surfactant concentration were studied, and high resolution was obtained using a 30 mM phosphate buffer (pH 7.0) containing 150 mM sodium dodecyl sulfate. The detection was by UV absorbance at 245 nm and the column was a fused-silica capillary of 67 cm×75 μm I.D.. The determination of these metabolites in human urine was completed within 15 min without any interferences.     

Determination of aloenin,barbaloin and isobarbaloin in Aloe species by micellar electrokinetic chromatography

Aloenin, barbaloin and isobarbaloin in JP Aloe¹, Aloe barbadensis (Aloe vera) and Aloe arborescens Miller var. natalensis Berger (Aloe arborescens Miller) were determined by micellar electrokinetic chromatography (MEKC) with 50 mM sodium dodecyl sulfate. Aloenin, barbaloin and isobarbaloin were well separated by MEKC and as little as 5.5 pg/11 nl of the three compounds could be detected. The determination took around 14 min.     

Monitoring of dithiothreitol clearance by means of micellar electrokinetic chromatography

A new method for specific determination of dithiothreitol (DTT) using micellar electrokinetic chromatography and on-column reaction with reactive disulfide-2,2'-dipyridyldisulfide is described. DTT in this reaction is quantitatively transformed into a mixed disulfide concomitantly with formation of equimolar amount of the 2-thiopyridone that is further separated by micellar electrokinetic chromatography and determined spectrophotometrically at 343 nm. The concentration of DTT is thus estimated indirectly from the result of 2-thiopyridone determination. The linear detection range for concentration versus peak area for the assay is from 0.05 to 2.5 mM (correlation coefficient 0.993) with a detection limit of 2.5 microM. The inter-day reproducibility of the peak area was 1.35% and the inter-day reproducibility of the migration time 0.56%. The method can be applied for DTT monitoring both in chemical and biological systems.     

Microemulsion and micellar electrokinetic chromatography of steroids

A mixture of ten steroids was separated by microemulsion and micellar (SDS and glycodeoxyholate) electrokinetic chromatography systems. Separations were done on a 50 cm (to the detector) × 50 μm I.D. fused-silica capillary. Complete separation of all the test compounds in the micellar mode was obtained with glycodeoxycholate (50 mM) in 25 mM borate buffer, pH 6.5, as the micelle-forming agent. The best results, however, were obtained using microemulsion electrokinetic chromatography in which higher aliphatic alcohols were used as the microemulsion-forming modifiers. The system consisted of n-hexanol (0.81%), SDS (3.31%) and n-butanol (6.61%) in 20 mM phosphate buffer, pH 10.0 (89.28%, w/w). In the microemulsion mode, linear calibration for steroid standards was obtained in the concentration range 3 × 10⁻⁴ − 3 × 10⁻⁵ mol l⁻¹ with a detection limit of 1 pmol. The method was validated and applied to an 11β-hydroxysteroid dehydrogenase assay in tissues.     

Determination of active components in rhubarb and study of their hydrophobicity by micellar electrokinetic chromatography

A micellar electrokinetic chromatographic (MEKC) method has been developed for the determination of five anthraquinones and one distyrene derivative in rhubarb. The separation conditions were optimized and two kinds of rhubarb plants and rhubarb-containing medicines were analyzed. The negatively charged solutes migrated toward the anode and were retarded by their interaction with the micelle. Hydrophobicity of the solutes was studied by both MEKC with SDS and SDS-free capillary zone electrophoresis in the buffer of 15 mmol/L NaH(2)PO(4)+ 20 mmol/L borax and 15% ethanol (v/v). Linear correlation between log k' and log P(OW) was obtained for the five anthraquinones in SDS micelle system. The capacity factor, k', and free energy differences delta(deltaG) derived from this method provided fundamental information on the interaction between the solutes and the micelle.     

Determination of biogenic amines in fish implicated in food poisoning by micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary chromatography (MECC) method for the simultaneous determination of seven biogenic amines in fish was developed. The peaks of all components were successfully separated within 11.5 min. MECC was performed with 0.06 M sodium deoxycholate in 0.02 M borate buffer (pH 9.2)–methanol (95:5, v/v) solvent. The average recoveries for all components ranged from 84.4 to 100.3%. The application of this method to detect amines in fried marlin fillet implicated in a food poisoning incident indicated that a high level (56.24 mg/100 g) of histamine was present in the sample. Another 10 fish samples collected from markets were also analyzed and did not contain detectable levels of histamine (<2.5 mg/100 g).     

Determination of creatinine and other uremic toxins in human blood sera with micellar electrokinetic capillary electrophoresis

We have been interested in the clinical use of capillary electrophoresis (CE) to monitor low-molecular-mass uremic toxins in body fluids. Creatinine, an important clinical marker for renal failure, is zwitterionic over a fairly wide pH range (pH 5–9) and can not be resolved from neutral components using free solution CE under these conditions. We report here a micellar electrokinetic capillary chromatography method using an sodium dodecyl sulfate-borate buffer system at pH 9.0 to determine creatinine levels in human serum. This method, performed on deproteinized sera, is also suitable for determining multiple ionic components. Moreover, this method compares favorably with an enzymatic method for creatinine performed in a clinical laboratory and thus appears to be a promising method in terms of potential clinical use.     

Determination of temozolomide in serum and brain tumor with micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatographic (MEKC) with photodiode-array detection was applied to determine temozolomide (TMZ) in human serum and brain tumor. The limit of quantitation (LOQ) was 0.096 μg/mL using 325 nm as detection wavelength. The method made possible that the TMZ could be detected in in vivo serum samples without sample pretreatment. In order to detect TMZ at lower concentration, an extraction with ethyl acetate was applied to preconcentrate the analyte. Small amount of brain tumor tissues (less than 1g) were lyophilized and pretreated using extraction as a clean up and concentrating step. After removing the organic solvent a final sample volume of only 10 μL was analyzed. The obtained peak concentrations (8.2-10.1 μg/mL) and T(max) (44-65 min) of TMZ in serum were similar to the data reported by others, the in vivo TMZ concentrations found in brain tumor ranged between 0.061 and 0.117 μg/g.     

Determination of serum creatinine by gas-liquid chromatography

The gas-liquid chromatographic measurement of serum creatinine is described in the present study. A preliminary concentration on cation exchange resin is used. The different steps of the operating procedure are analysed. A statistical comparison is undertaken between the results obtained with gas-liquid chromatography and kinetic colorimetry method using Jaffé assay.     

Chiral separation of vinpocetine using cyclodextrin-modified micellar electrokinetic chromatography

A cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) technique has been developed for enantioseparation of vinpocetine using an inexpensive 2-hydroxypropyl-β-CD (HP-β-CD) as the chiral selector (CS). The best chiral separation was achieved using 40 mM HP-β-CD as the CS in 50 mM phosphate buffer (pH 7.0) consisting of 40 mM sodium dodecyl sulfate (SDS) at a separation temperature and separation voltage of 25°C and 25 kV, respectively. To the author's best knowledge, this is the first CD-MEKC study able to successfully separate the four stereoisomer of vinpocetine in separation time of 9.5 min and resolution of 1.04-3.87.     

High resolution of oligosaccharide mixtures by ultrahigh voltage micellar electrokinetic capillary chromatography

Oligosaccharide mixtures released from ribonuclease B and human IgG have been separated using micellar electrokinetic capillary chromatography operated at 100 kV. The resolution of these closely related analytes at this high voltage was found to be superior to that obtained at 20 kV, a voltage which is ordinarily used in most capillary electrophoresis separations.     

Separation of new antidepressants and their metabolites by micellar electrokinetic capillary chromatography

Selective serotonin reuptake inhibitors (SSRIs), serotonin noradrenergic reuptake inhibitors (SNaRIs) and noradrenergic and specific serotoninergic antidepressant (NaSSA) are widely used in the treatment of depression. An increase in antidepressant intoxications led to the development of reliable analytical methods for their analysis. A new determination procedure for these compounds (milnacipran, venlafaxine, desmethylvenlafaxine, mirtazapine, desmethylmirtazapine, citalopram, desmethylcitalopram, fluvoxamine, paroxetine, sertraline and fluoxetine) was developed by micellar electrokinetic capillary chromatography (MEKC) with diode array detection (DAD). Separation and determination were optimised on an uncoated fused-silica capillary (600 mm, 75 microm I.D.). The migration buffer consisted of 20 mM sodium borate, pH 8.55, with 20 mM SDS and 15% isopropanol, at an operating voltage of 25 kV. The column temperature was maintained at 40 degrees C. Injection in the capillary was performed in the hydrodynamic mode (0.5 p.s.i., 15 s). In these conditions, the migration time of the antidepressants was less than 11 min. In most cases, calibration curves were established for 30 - 2000 ng/ml (r > 0.995). The limit of detection and the limit of quantification were ranged between 10 and 20 and between 20 and 30 ng/ml, respectively, for all the molecules. This method allowed the determination of some of these compounds in biological fluids (blood, urine) in post-mortem cases. Samples (1 ml) were extracted with diethyl ether (5 ml) at pH 9.6 and reconstituted in diluted migration buffer. Similar results were obtained by a HPLC-DAD determination, performed as a reference method. These results suggest that this MEKC method can be useful for the determination of new antidepressants in post-mortem cases.