Determination of folic acid by capillary electrophoresis with chemiluminescence detection

A rapid and simple method is presented for the determination of folic acid (FA) by capillary electrophoresis (CE) with chemiluminescence (CL) detection. This method was based on enhance effect of FA on the CL reaction between luminol and BrO(-) in alkaline aqueous solution. Optimal separation and determination was obtained with an electrophoretic buffer of 35 mM sodium borate (pH 9.4) containing 0.8 mM luminol, and an oxidizer solution of 1.6 mM NaBrO in 100 mM NaCO(3) buffer solution (pH 12.0). Under the optimal conditions, the determination of FA was achieved in less than 20 min, and the detection limit was 2.0 x 10(-8) M (S/N=3). The relative standard deviations (RSDs) on peak area and migration time were in the 1.5 and 1.1%, respectively. The present CE-CL method was applied to the determination of FA in commercial pharmaceutical tablets, apple juices and human urine.     

Application of an external contactless conductivity detector for the analysis of beverages by microchip capillary electrophoresis

Quantitative total ionic analysis of alcoholic and nonalcoholic beverages was performed by microchip capillary electrophoresis with external contactless conductivity detection. An electrolyte solution consisting of 10.5 mM histidine, 50 mM acetic acid, and 2 mM 18-crown-6 at pH 4.1 was used for the determination of NH(4) (+), K(+), Ca(2+), Na(+), and Mg(2+). Fast analysis of Cl(-), NO(3) (-), and SO(4) (2-) was achieved in 20 mM 2-(N-morpholino)ethanesulfonic acid /histidine electrolyte solution at pH 6.0 and the simultaneous separation of up to 12 inorganic and organic anions was performed in a solution containing 10 mM His and 7 mM glutamic acid at pH 5.75. Limits of detection ranged from 90 to 250 mug/L for inorganic cations and anions, and from 200 to 2000 mug/L for organic anions and phosphate. Calibration curves showed linear dependencies over one to two orders of magnitude when the stacking effect was minimized by injecting standard solutions prepared in background electrolyte solutions. Total analysis times of 35 and 90 s were achieved for the determination of 5 inorganic cations and for the simultaneous determination of 12 inorganic and organic anions, respectively, which represents a considerable reduction of analysis time compared to conventional separation methods used in food analysis.     

Electrochemical Design of Ultrathin Palladium Coated Gold Nanoparticles as Nanostructured Catalyst for Amperometric Detection of Formaldehyde

An underpotential deposition (UPD) replacement tactic was employed to design a Pd overlayer on gold (Au) nanoparticles electrodeposited on a carbon ionic liquid electrode (CILE). Pd/Au/CILE was applied as an amperometric sensor for the determination of formaldehyde in aqueous solutions. The sensor displayed two linear ranges from 15 µM–1.4 mM and 1.4–56.7 mM of formaldehyde. The limit of detection was 3 µM of formaldehyde and the sensitivity of the sensor was 2.35 µA mM^?1, using the calibration graph in the lower range. The presence of 20 mM of formic acid and methanol and 10 mM ethanol did not interfere with the determination of formaldehyde solution.     

Flow-injection determination of 3-hydroxybutyrate in serum with an immobilized 3-hydroxybutyrate dehydrogenase reactor and fluorescence detection

A flow-injection system with an immobilized enzyme reactor is proposed for the determination of 3-hydroxybutyrate. 3-Hydroxybutyrate dehydrogenase is immobilized on aminated poly(vinyl alcohol) beads and packed into a stainless-steel column (4 cm x 4 mm I.D.). Serum is diluted and filtered. Sample solution (20 mul) is injected into the carrier stream [4mM NAD(+) in glycine buffer (pH 9.3)]. The NADH formed is detected at 465 nm (excitation at 340 nm). The calibration graph is linear for 0.7-500muM 3-hydroxybutyrate; the detection limit is 0.5muM.     

Determination of inorganic cations and anions by ion-exchange chromatography with evaporative light-scattering detection

Evaporative light-scattering detection (ELSD) was investigated for the direct determination of alkali and alkaline-earth cations by cation-exchange chromatography. Successful single run analysis of Na+, K+, Mg2+ and Ca2+ was achieved in 11 min on the Hamilton PRP-X200 column using an aqueous solution of ammonium formate as mobile phase under a salt concentration step gradient mode (20 mM and 100 mM). Surprisingly the use of ELSD reveals a weak retention of inorganic anions (Cl-, NO3-, SO4(2-)) onto the polymeric cation exchanger, which enables the simultaneous determination of inorganic anions (C1- and NO3-) associated with the cations analysed (Na+ and K+).     

Study of major flavonoids in crude Scutellariae Radix by micellar electrokinetic capillary chromatography

A method of micellar electrokinetic capillary electrophoresis for determining the six flavonoids in Scutellariae Radix (i.e., baicalin, baicalein, wogonin 7-O-glucuronide, wogonin, oroxylin A 7-O-glucuronide, and oroxylin A) has been developed. The buffer solution (pH 7.24) composed of 20 mM sodium dodecyl sulfate (SDS), 20 mM sodium dihydrogen phosphate, and 25 mM sodium borate was found to be the most suitable electrolyte for the separation. The contents of the six flavonoids in crude Scutellariae Radix could easily be determined within about 15 min. On-column UV (254 nm) monitoring allowed the quantitative determination of baicalin. The effects of pH, surfactant concentration, and applied voltage on the migration behavior of the solutes were studied.     

Spectrophotometric determination of phosphate anion based on the formation of molybdophosphate in ethylene glycol-water mixed solution

New appropriate reaction system was found for spectrophotometric determination of phosphate anion. This spectrophotometric method is based on the color development due to the formation of yellow molybdophosphate anion in acidic ethylene glycol-water (EG-W) mixed solution containing Mo(VI) species. The solution containing e.g. 20 mM Na(2)MoO(4), 0.1 M HCl, and 40% (v/v) EG is colorless, and becomes immediately yellow by addition of phosphate anion. Thus the method is simple, rapid, and easy to carry out. Although Si(IV) species is well known to interfere with the determination of phosphate anion in many cases, the EG-W Mo(VI) solution remains colorless after addition of silicate anion at 1 mM level, indicating that no yellow molybdosilicate anion was formed in the EG-W solution. Under an optimized condition, the absorbance at e.g. 400 nm of the EG-W P(V)-Mo(VI) solution was proportional to the concentration of phosphate anion with good reproducibility, and the detection limit was 1 μM. Also the present method is less interfered by high concentrations of potassium and ammonium cations and oxidative nitrite anion as well as silicate anion.     

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.     

Extracting kinetic parameters for homogeneous [Os(bpy)2ClPyCOOH]+ mediated enzyme reactions from cyclic voltammetry and simulations

The homogeneous reaction between glucose oxidase and osmium bipyridine-pyridine carboxylic acid in the presence of glucose has been studied in detail by cyclic voltammetry and digital simulation. Combination of the analytical equations that describe the dependence of the amperometric response on enzyme, substrate and co-substrate concentrations for the limiting cases with digital simulation of the coupled enzyme reaction diffusion problem allows us to extract kinetic parameters for the substrate-enzyme reaction: K(MS)=10.8 mM, k(cat)=254 s(-1) and for the redox mediator-enzyme reaction, k=2.2x10(5) M(-1) s(-1). The accurate determination of the kinetic parameters at low substrate concentrations (<7 mM) is limited by depletion of the substrate close to the electrode surface. At high substrate concentrations (>20 mM) inactivation of the reduced form of glucose oxidase in the bulk solution must be taken into account in the analysis of the results.     

Rapid and simple pretreatment of human body fluids using electromembrane extraction across supported liquid membrane for capillary electrophoretic determination of lithium

Electromembrane extraction was used for simultaneous sample cleanup and preconcentration of lithium from untreated human body fluids. The sample of a body fluid was diluted 100 times with 0.5 mM Tris solution and lithium was extracted by electromigration through a supported liquid membrane composed of 1-octanol into 100 mM acetic acid acceptor solution. Matrix compounds, such as proteins, red blood cells, and other high-molecular-weight compounds were efficiently retained on the supported liquid membrane. The liquid membrane was anchored in pores of a short segment of a polypropylene hollow fiber, which represented a low cost, single use, disposable extraction unit and was discarded after each use. Acceptor solutions were analyzed using capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4) D) and baseline separation of lithium was achieved in a background electrolyte solution consisting of 18 mM L-histidine and 40 mM acetic acid at pH 4.6. Repeatability of the electromembrane extraction-CE-C(4) D method was evaluated for the determination of lithium in standard solutions and real samples and was better than 0.6 and 8.2% for migration times and peak areas, respectively. The concentration limit of detection of 9 nM was achieved. The developed method was applied to the determination of lithium in urine, blood serum, blood plasma, and whole blood at both endogenous and therapeutic concentration levels.     

Quality evaluation of Guan‐Xin‐Ning injection based on fingerprint analysis and simultaneous separation and determination of seven bioactive constituents by capillary electrophoresis

The purpose of this study was to develop a comprehensive, rapid and practical capillary electrophoresis (CE) method for quality control (QC) of Guan‐Xin‐Ning (GXN) injection based on fingerprint analysis and simultaneous separation and determination of seven constituents. In fingerprint analysis, a capillary zone electrophoresis (CZE) method with a running buffer of 30 mM borate solution (pH 9.3) was established. Meanwhile, ten batches of samples were used to establish the fingerprint electropherogram and 34 common peaks were obtained within 20 min. The RSD of relative migration times (RMT) and relative peak areas (RPA) were less than 5%. In order to further evaluate the quality of GXN injection, a micellar electrokinetic chromatography (MEKC) method was developed for simultaneous separation and determination of bioactive constituents. Seven components reached baseline separation with a running buffer containing 35 mM SDS and 45 mM borate solution (pH 9.3). A good linearity was obtained with correlation coefficients from 0.9906 to 0.9997. The LOD and LOQ ranged from 0.12 to 1.50 μg/mL and from 0.40 to 4.90 μg/mL, respectively. The recoveries ranged between 99.0 and 104.4%. Therefore, it was concluded that the proposed method can be used for full‐scale quality analysis of GXN injection.     

Capillary electrophoresis determination of six bioactive constituents in San-huang-hsieh-hsin-tang

A capillary electrophoretic method for simultaneous determination of six bioactive ingredients (berberine, palmatine, baicalin, sennoside B, emodin, and sennoside A) in the Chinse herbal formula San-huang-hsieh-hsin-tang was established. A carrier composed of aqueous buffer solution (50 mM sodium cholate, 15 mM sodium dihydrogen phosphate, and 4.25 mM sodium borate)-acetonitrile (3:2) was found to be the most suitable electrolyte for this separation. Contents of these constituents in a non-pretreated methanol-water extract of San-huang-hsieh-hsin-tang sample could be easily determined within 20 min. The effects of borate, cholate, and organic modifier (acetonitrile) concentration of the carrier on the migration behavior of the solutes were also studied.     

Separation and Determination of Five Anthraquinones in Rheum and Rheum-Containing Preparations by Capillary Zone Electrophoresis

A capillary zone electrophoresis method modified by β-CD was, for the first time, developed for the simultaneous determination of five anthraquinones (physcion, chrysophanol, aloe-emodin, emodin and rhein) in rheum and rheum-containing preparations. The factors relevant to the run buffer media and their effects on the separation were studied. A buffer solution composed of 15 mM sodium borate, 30 mM β-CD, 20% acetonitrile and 1.0% ethanediol was found to be the most suitable electrolyte for separation, whereby the contents of the five anthraquinones in rheum and rheum-containing preparations could be easily determined in 20 min at 20 kV. The relative standard deviation for the determination of the five constituents in the samples varied form 0.16–5.47%, and the recovery ranged between 92.0 and 107.3%. Moreover the inclusion constants of the target compounds, except for rhein with β-CD, were also determined.     

Flow injection method for sulfide determination by the methylene blue method

Flow injection determination of sodium sulfide and hydrogen sulfide in solution through the methylene blue spectrophotometric procedure is described. The carrier streams are N,N-dimethylaniline sulfate (5.4 mM, HCl solution) and iron(m) ammonium sulfate (14.2 mM, HCl solution) and are merged before injection of sulfide (in 0.01 M NaOH). The sampling rate is 210 per hour. The effect of reagent concentrations and interferents on the determination has been investigated.     

Nonaqueous capillary electrophoresis method for the analysis of gleevec and its main metabolite in human urine

The viability of nonaqueous capillary electrophoresis (NACE) was investigated for determination of gleevec and its main metabolite in human urine using a fused-silica capillary. Baseline separation of the studied solutes was obtained using a nonaqueous solution composed of 12 mM ammonium acetate and 87.6 mM acetic acid in methanol-acetonitrile (ACN) (80:20, v:v) providing analysis time shorter than 3 min. Different aspects including stability of the solutions, linearity, accuracy and precision were studied in order to validate the method in the urine matrix. Detection limits of 24 microg L(-1) for gleevec and its metabolite were obtained. A robustness test of the method was carried out using the Plackett-Burman fractional factorial model with a matrix of 15 experiments. The developed method is simple, rapid and sensitive and has been used to determine gleveec and its metabolite at clinically relevant levels in human urine. Before NACE determination, a solid-phase extraction (SPE) procedure with a C18 cartridge was necessary. Real determination of these analytes in two patient urines were done.     

Simultaneous determination of nanomole amounts of sulphur dioxide and hydrogen sulphide by flow injection analysis with on-line preconcentration by means of capillary denuder tubes

A simple and rapid method for trace determination of SO2 and H2S in gaseous samples by using a flow injection system with on line preconcentration on capillary denuder is described. The gaseous samples are led through a 0.4 M sulphamic acid solution, retaining nitrogen dioxide, ammonia and hydrogen chloride. The sulphur dioxide is collected from the carrier gas stream (250 cm3 min-1) as sulphuric acid in a capillary denuder tube coated with a thin layer of 0.01-0.03 M hydrogen peroxide solution of 0.05 mM sulphuric acid; hydrogen sulphide passes into a second tube coated with 0.075 mM sodium sulphide solution of 0.1 M aqueous sodium hydroxide. The films containing the sulphuric acid and the sodium sulphide, respectively, are eluted with the corresponding circulating absorbent streams and pass through the detectors. Sulphuric acid is detected by conductimetry and sulphide is determined spectrophotometrically at 230 nm. If nanoequivalent amounts of H2S are present in the sample containing a large concentration of SO2 (SO2/H2S concentration ratio > 20), the sulphur dioxide is filtered out of the sample gas stream by solid sodium hydrogen carbonate. A limit of detection of 3.5 micrograms m-3 is obtained.     

Quantitation of caffeine by capillary zone electrophoresis with end-column amperometric detection at a carbon microdisk array electrode

Capillary zone electrophoresis is employed for the determination of caffeine using end-column amperometric detection with a carbon fiber microdisk array electrode at a constant potential of 1.45 V versus a saturated calomel electrode. The optimum conditions of separation and detection are 0.1 52mM NaH2PO4-0.648mM Na2HPO4 for the buffer solution, 20 kV for the separation voltage, 5 kV for the injection voltage, and 10s for the injection time. The limit of detection is 2.9 x 10(-4)mM or 1.2 fmol (signal-to-noise ratio = 2). The relative standard deviation is 0.68% for the migration time and 2.3% for the electrophoretic peak current. The method is applied to determining caffeine in human serum and a cola drink.     

Direct simultaneous determination of eight sweeteners in foods by capillary isotachophoresis

A method for isotachophoretic determination of sweeteners of different character in candies and chewing gums was developed. A capillary of 0.8 mm ID and 90 mm effective length made of fluorinated ethylene-propylene copolymer is filled with an electrolyte system consisting of 10 mM HCl + 14 mM Tris, pH 7.7 (leading electrolyte) and 5 mM L-histidine + 5 mM Tris, pH 8.3 (terminating electrolyte). The analysis is performed at a driving current of 200 microA and for detection current is decreased to 100 microA. Boric acid is added to the aqueous sample solution to form borate complexes with substances of polyhydroxyl nature and make them migrate isotachophoretically. Using conductivity detection, the calibration curves in the tested concentration range up to 2.5 mM were linear for all components of interest: acesulfame K, saccharine, aspartame, cyclamate, sorbitol, mannitol, lactitol, and xylitol. The concentration detection limits ranged between 0.024 and 0.081 mM. Good precision of the ITP method is evidenced by favorable RSD values ranging from 0.8 to 2.8% obtained at the analyte concentration of 1.0 mM (n = 6). The analysis time was about 20 min. Simplicity, accuracy, and low cost of analyses make ITP an alternative procedure to methods used so far for the determination of ionizable sweeteners.     

Determination of nonylphenol and nonylphenol ethoxylates in wastewater using MEKC

Nonylphenol ethoxylates (NPEO_x) are surfactants which are used worldwide and can be transformed in the environment by microorganisms to form nonylphenol (NP). Analysis of these compounds was carried out with micellar electrokinetic capillary chromatography (MEKC). Different parameters such as background electrolyte (BGE) solution, pH, type of surfactant, and sample stacking were optimized. The use of CHES (20 mM, pH 9.1) in combination with 50 mM sodium cholate as a surfactant as BGE solution, together with sample stacking using 50 mM NaCl in the sample and an injection time of 20 s, provided the best separation of the compounds studied. The method was applied to the determination of target analytes in two types of sludge water coming from two steps of a wastewater treatment plant. Liquid–liquid extraction was carried out using toluene as solvent, resulting in recoveries around 100% for all studied analytes. The presence of NPEO_x was observed in the first step of the sludge water treatment, based on migration time and UV spectra. Identification was confirmed using tandem MS. LOQs of the studied compounds were in the range of 12.7 to 30.8 ng/mL, which is satisfactory for the analysis of real wastewater samples.     

Quantitation of talinolol and other beta-blockers by capillary electrophoresis for in vitro drug absorption studies

A capillary zone electrophoresis method is described for the enantioseparation of talinolol using heptakis(2,3-diacetyl-6-sulfo)-beta-cyclodextrin (HDAS-beta-CD) as a chiral selector. After liquid-liquid extraction of talinolol from physiological solution, electrokinetic injection was employed to improve the sensitivity. The use of a coated capillary was necessary to achieve stable and reproducible enantioseparations. A baseline separation of the talinolol enantiomers was achieved in less than 10 min using 100 mM phosphate solution as background electrolyte and pH 3.5, at the presence of 3.0 mM HDAS-beta-CD and at 20 degrees C. In addition, this analytical condition proved to be useful for the enantioseparation of a number of other beta-blocking agents such as alprenolol, atenolol, bisoprolol, celiprolol, metipranolol, oxprenolol, and sotalol. For determining talinolol, the method could be validated in terms of precision, accuracy and linearity, and was found to be suitable in determination of talinolol enantiomers in highly diluted samples obtained from in vitro experiments.