Separation of Sulfur Species in Water by Co-Electroosmotic Capillary Electrophoresis with Direct and Indirect UV Detection

Co-electroosmotic capillary electrophoresis (co-CZE) with both direct and indirect UV detection was investigated for the separation of sulfur species. With direct UV detection, the separation of S₂O^2? ₃, S₂O^2? ₄ was possible using 20 mM phosphate electrolyte containing 0.75 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile. To obtain optimal peak shape and sensitivity using indirect UV detection, a range of background electrolytes (BGEs), including benzoate, phthalate, 2,6-pyridinedicarboxylate (2,6-PDCA) and trimellitate, were examined as the BGEs. Of all the BGEs, 2,6-PDCA gave high selectivity and indirect UV response due to its mobility matching to that of sulfur species and its high absorptivity. Detection limits in range of 3-6 μM were obtained using either direct UV or indirect UV detection. The proposed CZE methods were used for the determination of sulfur species in water samples, and provided fast separation of sulfur species in less than 5 min.     

Electrophoretic behavior of adamantane derivatives possessing antiviral activity and their determination by capillary zone electrophoresis with indirect detection

Separation and determination of adamantane derivatives with antiviral activity, namely amantadine (1-adamantan amine), memantine (1-amino-3,5-dimethyl adamantane) and rimantadine (alpha-methyl-1-adamantane methylamine), were examined by capillary zone electrophoresis. After optimization, an indirect detection method using 5 mM 4-methylbenzylamine in ethanol/water solution (1:4) as simultaneously absorbing and buffering background electrolyte with detection at 210 nm was found suitable for determination of the individual compounds (limit of detection was 0.35 mg L(-1) for memantine hydrochloride, S/N = 3). Baseline separation of all the three compounds was reached by addition of alpha- or beta-cyclodextrins to the electrolyte in concentrations of 20 and 2 mM, respectively.     

Simultaneous Determination of Atenolol and Chlorthalidone in Pharmaceutical Preparations by Capillary-Zone Electrophoresis

Abstract

A capillary zone electrophoresis (CZE) method for the simultaneous determination of the β-blocker drugs atenolol and chlorthalidone in pharmaceutical formulations has been developed. The CZE separation was performed under the following conditions: capillary temperature, 25°C; applied voltage, 25 kV; 20 mM H₃PO₄–NaOH running buffer (pH 9.0); and detection wavelength, 198 nm. Phenobarbital was used as internal standard. The method was validated and showed not only good precision and accuracy but also good robustness. The method has been successfully applied to the simultaneous determination of both atenolol and chlorthalidone in pharmaceutical tablets.     

Optimization,Validation and Application of a Capillary Zone Electrophoresis Method for the Assay of Sparfloxacin in Pharmaceutical Formulation

Abstract

A capillary zone electrophoresis (CZE) method has been developed for the determination of the antibiotic sparfloxacin in tablets. The CZE separation was performed using 75 µm×35 cm fused-silica capillary under the following conditions: 25°C; applied voltage, 12 kV; 25 mM H₃PO₄-NaOH running buffer (pH 8.5). The detection wavelength was 254 nm. Flumequine was used as internal standard (IS). The method was suitably validated with respect to linearity, limit of detection and quantification, accuracy, precision, specificity, and robustness. The calibration was linear from 10 to 60 µg mL^?1 and the limit of detection and quantification were 5.38 and 9.46 µg mL^?1, respectively. Recoveries ranging from 95.68%–102.4% were obtained in the determination of sparfloxacin that were spiked to placebos. Excipients in the commercial tablets and degraded products from different stress conditions did not interfere in the assay. The method was successfully applied to the determination of sparfloxacin in pharmaceutical tablets.     

Determination of Vecuronium Bromide in Pharmaceuticals: Development, Validation and Comparative Study of HPLC and CZE Analytical Methods

Vecuronium bromide is a neuromuscular blocking agent used for anesthesia to induce skeletal muscle relaxation. HPLC and CZE analytical methods were developed and validated for the quantitative determination of vecuronium bromide. The HPLC method was achieved on an amino column (Luna 150 × 4.6 mm, 5 μm) using UV detection at 205 nm. The mobile phase was composed of acetonitrile:water containing 25.0 mmol L^?1 of sodium phosphate monobasic (50:50 v/v), pH 4.6 and flow rate of 1.0 mL min^?1. The CZE method was achieved on an uncoated fused-silica capillary (40.0 cm total length, 31.5 cm effective length and 50 μm i.d.) using indirect UV detection at 230 nm. The electrolyte comprised 1.0 mmol L^?1 of quinine sulfate dihydrate at pH 3.3 and 8.0% of acetonitrile. The results were used to compare both techniques. No significant differences were observed (p > 0.05).     

Application of co-electroosmotic capillary electrophoresis for the determination of inorganic anions and carboxylic acids in soil and plant extract with direct UV detection

Summary Indirect UV detection in capillary zone electrophoresis (CZE) is frequently used for the determination of inorganic anions and carboxylic acids. However, there are few reports on direct UV detection of these solutes in real samples. This paper describes the use of direct UV detection of inorganic anions and organic acids in environmental samples using co-electroosmotic capillary zone electrophoresis (co-CZE) at 185 nm. The best separation and detection of the solutes was achieved using a fused silica capillary with an electrolyte containing 25 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile (v/v) at pH 6.0. Four common inorganic anions (Cl⁻, NO₂ ⁻, NO₃ ⁻ and SO₄ ²⁻) and 11 organic acids (oxalic, formic, fumaric, tartaric, malonic, malic, citric, succinic, maleic, acetic, and lactic acid), were determined simultaneously in 15 min. Linear calibration plots for the test solutes were obtained in the range 0.02–0.5 mM with detection limits ranging from 1–9 μM depending on the analyte. The proposed method was successfully used to determine inorganic anions and carboxylic acids in soil and plant tissue extracts with direct injection of the sample.     

Separation of amino acids in plant tissue extracts by capillary zone electrophoresis with indirect UV detection using aromatic carboxylates as background electrolytes

Summary Amino acids in extracts of plant tissue were separated and detected by capillary zone electrophoresis (CZE) with indirect UV detection. Various aromatic carboxylates such as salicylate, benzoate, phthalate and trimellitate were investigated as background electrolytes (BGEs). A BGE of benzoate gave the best resolution and detector response. Amino acids were separated at a highly alkaline pH to charge amino acids negatively. Separation was achieved by the co-electroosmotic flow (Co-EOF) by the addition of the cationic surfactant myristyltrimethyl-ammonium bromide (MTAB) to the electrolyte. The condtions affecting the separation of amino acids, including electrolyte pH, concentrations of both benzoate and MTAB, were investigated and optimised. Separation of a mixture of 17 amino acids at pH 11.20 with indirect UV detection at 225 nm was achieved with a BGE of 10 mM benzoate containing 1.0 mM MTAB at pH of 11.20. Detection limits ranged between 10 and 50 μM. The proposed method was demonstrated by the determination of amino acids in extracts of Eucalypt leaves with direct injection of samples.     

Measurement of nitrate and chlorate in swimming pool water by capillary zone electrophoresis

Capillary zone electrophoresis (CZE) of nitrate and chlorate in swimming pool water are described. Nitrate and chlorate were determined simultaneously with an indirect detection method in an electrolyte containing 10 mM chromate and 0.1 mM cetyltrimethylammonium bromide (CTAB). Where chloride concentration was so high that nitrate could not be determined satisfactorily because of interference, a direct detection technology was developed in which 10 mM sulfate and 0.1 mM CTAB were used as the buffer. The wavelength for indirect detection was 254 nm and 214 nm for direct detection. Relative standard deviations of the quantification of nitrate and chlorate in real samples were below 6%. The detection limits were 7 mug ml(-1) for chlorate, and 4 mug ml(-1) (indirect detection) and 0.4 mug ml(-1) (direct detection) for nitrate.     

Comparison of shikimic acid determination by capillary zone electrophoresis with direct and indirect detection with liquid chromatography for varietal differentiation of red wines

Two capillary zone electrophoretic (CZE) methods for determination of shikimic acid in Chilean red wine were developed and compared with a HPLC method. Both electrophoretic methods were carried out by using a reversed electroosmotic flow induced by trimethyl(tetradecyl)ammoniumbromide (TTAB) with indirect detection at 260 nm using p-aminobenzoic acid as a UV-absorbing co-ion or by direct detection at 213 nm. In both cases, the separation was carried out in a 50 microm I.D. uncoated capillary with an effective length of 48 cm, a negative power supply of 30 kV, using a buffer based on bis[2-hydroxyethyl]imino-tris[hydroxymethyl]methane (Bis-Tris), pH 7.0 or 7.5 and hydrodynamic injection. The chromatographic separations were carried out on a C-18 reversed phase column followed by a sulfonyl-styrene-divinylbenzene (S-DVB) ion exclusion column at 70 degrees C with H2SO4 0.02 M as isocratic mobile phase and a flow rate of 0.5 mL min(-1). The three methods allowed the quantification of shikimic acid with quantification limits between 1.0 and 12.0 mg L(-1) and precision between 7.3 and 10.1%, however, only the concentrations obtained by CZE with direct detection were statistically similar to those of HPLC. This parameter was evaluated as analytical tool to verify varietal authenticity of red wines. In all cases, the Cabernet Sauvignon wines presented higher concentrations of shikimic acid, compared with Merlot or Carmenère wines.     

Determination of Phenolic Acids in Herba Epilobi by ITP–CE in the Column-Coupling Configuration

The combination of capillary isotachophoresis (ITP) and capillary zone electrophoresis (CZE) in the column-coupling configuration has been optimized in a mode in which the background electrolyte employed in the CZE step was different from the leading and terminating electrolytes of the ITP step. The optimum composition of the electrolyte system was 0.01 M HCl, 0.02 M IMI, 0.2% HEC, pH 7.2 (leading electrolyte), 0.01 M HEPES, pH 8.2 (terminating electrolyte), and 25 mM MES, 50 mM TRIS, 30 mM boric acid, 0.2% HEC, pH 8.3 (background electrolyte). All solutions contained 20% methanol. The timing of the transfer of isotachophoretically stacked analyte zones into the CZE column was also optimized. An ITP–CZE method with UV detection at 270 nm was developed for separation of nine phenolic acids (protocatechuic, syringic, vanillic, cinnamic, ferulic, caffeic, ρ-coumaric, chlorogenic, and gentisic acids) in a model mixture and used for assay of some of these acids in a methanolic extract of herba epilobi. Application of ITP–CZE resulted in 100-fold better sensitivity than conventional CZE; limits of detection ranged between 10 and 60 ng mL⁻¹. When MES–TRIS–borate-based buffer, pH 8.3, was used in the CZE separation step the linearity of the ITP–CZE response was satisfactory (correlation coefficients were from 0.9937 to 0.9777). Repeatability was also satisfactory (RSD values ranged between 0.77% and 1.28% for migration times and between 1.65% and 13.69% for peak area). Revised: 23 March and 27 April 2006     

Separation of naturally occurring triterpenoidal saponins by capillary zone electrophoresis.

A high-performance capillary electrophoresis (HPCE) was successfully applied to the separation and quantitation of naturally occurring oleanene triterpenoidal saponins. The HPCE adapted to the separation of two pairs of disteriomeric saponins (1-2) or (3-4), obtained from Trifolium alexandrinum seeds, was based on capillary zone electrophoresis (CZE) in borate buffer with UV detection at 195 nm. An usual technique for isolation and group separation of saponins was developed as an appropriate purification step prior to determination of individual saponins by CZE. The separation parameters such as borate concentration, pH and applied voltage were varied in order to find the best compromise that complied with demands for high separation, short duration and sufficiently high detector response. The optimum running conditions were found to be 60 mM borate buffer, pH 10 and 12 kV. Under the alkaline borate electrolyte, no resolution was achieved for the saponins (1 and 3) or (2 and 4) in a single mixture, except when 20 mM beta-cyclodextrin was added to the running electrolyte. With the combined techniques of group separation, purification and CZE, a rapid and efficient method for the determination of naturally occurring diasteriomeric saponins is now available.     

Simultaneous determination, by capillary zone electrophoresis, of multiple components of different industrial products

Summary Four parabens (esters of 4-hydroxybenzoic acid), effective preservatives against the growth of bacteria, yeast, and mold in numerous industrial products, have been used in this work as model compounds to demonstrate the resolving power of capillary electrophoresis (CE). The simultaneous determination of methyl-(MP), ethyl-(EP), propyl-(PP), and butylparaben (BP) was achieved by capillary zone electrophoresis (CZE) with UV diode-array detection at 294 nm. When run voltage, temperature, and electrolyte concentration and pH were optimized the most effective separation was achieved within 7 min by use of 50 cm (effective length) fused silica capillary tubing and operation at 25kV and 20°C. Background electrolyte comprising 35 mM tetraborate buffer adjusted to pH 10.0 gave the best results. The limits of detection of the optimized method ranged from 0.65 μg mL⁻¹ for BP to 0.81 μg mL⁻¹ for MP; the relative standard deviation was between 0.35 and 0.50%. These results showed that the method enables the determination of the four parabens in commerially available cosmetic and pharmaceutical preparations containing some of the parabens and in an unidentified canned berry fruit juice.     

Trace ion analysis of sea water by capillary electrophoresis: determination of strontium and lithium pre-concentrated by transient isotachophoresis

The applicability of capillary zone electrophoresis (CZE) to ions having relatively low natural occurrences in sea water is limited by method's relatively poor concentration detection sensitivity. A combination of CZE with indirect UV detection and transient isotachophoresis (tITP) pre-concentration was developed to evolve the CZE practical utility towards the quantitative determination of the minor sea water cationic components, strontium and lithium. The ITP stacking criterion at the initial stage of a CZE separation was met by taking a highly mobile sodium, the principle matrix cation, to perform the role of a leading ion, whereas the moderately mobile sample macrocomponents, Ca2+ and Mg2+, acted as the terminating ion. The carrier electrolyte, consisting of 10 mM 4-methylbenzylamine and 1.5 mM citric acid at pH 4.8, was found to be optimal to accommodate both analyte cations in the ITP range and then separate them in the CZE mode, with relative standard deviations for migration times from 0.06-0.15% and for peak areas from 4-8%. The limits of detection were 1.3 mg l(-1) Sr2+ and 0.12 mg l(-1) Li+. The developed method was applied to the analysis of a surface sea water sample and a sea water reference material. The results were in good agreement with those obtained by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and electrothermal atomic absorption spectrometry (ET-AAS).     

Capillary electrophoresis analysis of fosfomycin in biological fluids for clinical pharmacokinetic studies

A feasible capillary zone electrophoresis (CZE) method with indirect UV and contactless conductivity detection was developed for the determination of fosfomycin, an antibiotic, in human plasma and microdialysis samples. Samples were collected from test persons during a clinical trial. The background electrolytes used consisted of 25 mM benzoic acid and 0.5 mM hexadecyltrimethylammonium bromide, adjusted with tris(hydroxymethyl)aminomethane solution to pH 6.95 for plasma, and to pH 8.05 for microdialysis samples. CZE separations of the anionic analyte were carried out with reversed electroosmotic flow directed towards the anode. The limit of detection was between 0.6 and 2 microg/mL, depending on the matrix and the detection method. No sample preparation was needed for microdialysis samples; for plasma samples, proteins were precipitated with methanol (1+2, v+v), and the supernatant was analyzed. The yield determined with spiked samples was about 100%, the reproducibility of the entire method, expressed by the RSD% of three independent determinations of fosfomycin in triplicate after spiking Ringer's solutions and plasma samples, respectively, was better than 8%. The method is thus well-suited for clinical studies for the determination of the antibiotic in biological fluids.     

Simultaneous determination of inorganic anions, carboxylic and aromatic carboxylic acids by capillary zone electrophoresis with direct UV detection

Co-electroosmotic capillary zone electrophoresis (CZE) with direct UV detection was developed for simultaneous determination of inorganic anions, carboxylic and aromatic carboxylic acids. These solutes were separated using a 30 mM phosphate buffer containing 1.0 mM tetradecyltrimethylammonium bromide (TTAB) and 20% (v/v) acetonitrile at pH of 6.5 and directly detected by UV at 190 nm. Calibration curves were linear in the range 0.01-2.0 mM, depending of the solutes. The detection limits ranged from 1.0 to 8.0 microM and the relative standards deviations (n=5) in range from 1.9 to 3.6% for the peak area. The proposed method was used to determine inorganic anions and carboxylic and aromatic acids in soil and plant tissue extracts.     

Separation and Determination of D-Gluconic Acid Produced During Fermentation by Capillary Zone Electrophoresis

Abstract

A novel method was developed for separation and determination of D-gluconic acid produced during fermentation by capillary zone electrophoresis (CZE) with direct UV detection at 214 nm, using selected carrier electrolyte composed of 6 mM potassium biphthalate, 50 mM disodium hydrogen phosphate and 15% (v/v) acetonitrile. The effects of concentration of phthalate, phosphate and organic modifier (acetonitrile), as well as temperature for the separation were investigated. The method is simple, inexpensive and will make it very useful in the gluconic acid industry.     

Determination of purines and pyrimidines in beer samples by capillary zone electrophoresis

Ten purine and pyrimidine bases were separated using capillary zone electrophoresis (CZE) with direct UV detection at 254 nm as well as mass spectrometric (MS) detection using an electrospray ionization (ESI) interface. For this purpose a carrier electrolyte composition compatible with both methods of detection containing 300 mM diethylamine (DEA) was selected. Limits of detection were in the range between 0.1 and 0.3 mg l⁻¹ and calibration plots were found to be linear over at least two orders of magnitude. The applicability of the developed method for the analysis of real samples was demonstrated for some beer samples. A series of “Lager” beer samples from different breweries in Europe as well as a number of completely different types of beers were investigated with respect to their content in the selected purine and pyrimidine bases using the developed CE method with UV detection at 254 nm.     

Isotopic separation of lithium ions by capillary zone electrophoresis

Separation of ⁶Li and ⁷Li isotopes by CZE was demonstrated. The BGE contained 5 mM 4‐aminopyridine, 0.9 mM oxalic acid, 0.25 mM CTAB, and 0.25% w/v Tween 20 (рН = 9.2). The running conditions were +25 kV at 30°C with indirect photometric detection at 261 nm. Under optimal experimental conditions, the analysis time was less than 21 min. Separation of Li preparations with mole fraction of ⁶Li ranging from 3.44 up to 90.38% was demonstrated.     

Determination of ethyl glucuronide in human serum by hyphenation of capillary isotachophoresis and zone electrophoresis

The determination of ethyl glucuronide (EtG), a marker of recent alcohol consumption, in human serum by hyphenation of capillary ITP (CITP) and CZE is reported. For CITP step, 1 x 10(-2) M hydrochloric acid adjusted with epsilon-aminocaproic acid (EACA) to pH 4.4 was used as the leading electrolyte, and 1 x 10(-2) M nicotinic acid with EACA, pH 4.4, was used as the terminating electrolyte (TE). All electrolytes contained 0.2% hydroxypropylcellulose to suppress electroosmosis. In CITP, EtG was separated from fast serum macrocomponents chloride, phosphate, lactate, and acetate. Zones of microcomponents including EtG that migrated between acetate and nicotinate were forwarded to the second capillary filled with a BGE identical with the TE. Conductivity detection was used in the CITP step. Sensitive detection in the CZE step was performed using indirect spectrophotometric detection at 254 nm. The assay is based on a 1:5 dilution of serum with deionized water and has a concentration LOD for EtG in diluted sample of 9.8 x 10(-9) M. The method was used for the determination of EtG in sera of volunteers consuming alcohol.     

Determination of sugars using ligand-exchange capillary electrophoresis

The capabilities of the ligand-exchange capillary electrophoresis mode (working electrolyte, 1 mM copper(II) and 175 mM NH3; 30 mbar, 10 s; +25 kV; 245 nm; 20°C) for the determination of sugars (glucose, fructose, and sucrose) in real samples (fruit juices, wines, and drug preparations) were studied. With the use of glucose as an example, the detection limits for direct (as sugar—copper(II) complexes; 245 nm) and indirect (working electrolyte, 5 mM tryptophan and 50 mM NaOH; 30 mbar, 10 s; +10 kV; 280 nm; 20°C) UV detection were compared: ≈21 and ≈8 mg/L (for direct and indirect detection, respectively).