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In this work, an on-line preconcentration method of field-enhanced sample injection (FESI) was implemented in the determination of four β2-agoinsts terbutaline (TER), procaterol (PRO), formoterol (FOR) and bambuterol (BAM) by capillary electrophoresis coupled with capacitively coupled contactless conductivity detection (CE-C4D). Under optimized conditions the background electrolyte (BGE) was 5mM Tris(hydroxymethyl)aminomethane (Tris) and 10mM citric acid (Cit) at a pH of 3.2 while the sample dilution solution was obtained by methanol. The detection limits (defined as S/N=3) of this method were 0.02mg/L for TER, PRO, FOR, BAM, which were much lower than that of the conventional CE-C4D method without preconcentration procedure, the enhancement factors were greatly improved to be 30-40-fold. The linearity ranges of four β2-agoinsts were 0.1-15mg/L, with good linear correlation coefficients (r2>0.9900). In order to evaluate the application potential of the developed method, real sample from pig feed was analyzed with recoveries of 91.4-106.2%.

Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis–chemiluminescence (CE-CL) detection method for phenols using a hemin–luminol–hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br− and F− could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE-CL detection system because of the self-polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin–luminol afforded a stable CE-CL baseline. The indirect CE-CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10−8 mol/L (o-sec-butylphenol), 4.9 × 10−8 mol/L (o-cresol), 5.4 × 10−8 mol/L (m-cresol), 5.3 × 10−8 mol/L (2,4-dichlorophenol) and 7.1 × 10−8 mol/L (phenol). Copyright © 2013 John Wiley & Sons, Ltd.

Little is known about human polyol metabolism, but recent studies indicate that abnormal polyol concentrations in body fluids are related to several diseases. In this study, a rapid and sensitive method for the determination of seven major polyols in urine including two groups of polyol isomers, C5-polyols (Rib+Arb+Xyl) and C6-polyols (Sor+Gal+Man), was developed using capillary zone electrophoresis coupled with amperometric detection (CZE-AD). The effects of the working electrode potential, pH, running buffer components and concentrations, separation voltage and injection times were investigated. Under the optimised conditions, seven types of polyols could be perfectly separated via the formation of anionic polyol-borate complexes in a borate buffer solution. Highly linear current responses to the polyol concentrations were obtained with good correlation (0.9984

A quantitative determination of six neuroactive amino acids (NAAs) was performed by capillary zone electrophoresis with amperometric detection (CZE-AD). This CZE-AD method utilized two electrolytes: the borate solution flowing in a capillary has the NAAs-separation effects, and the sodium hydroxide (NaOH) solution filled in the detection reservoir for the amperometric analysis of NAAs. The following experimental parameters were optimized: the working electrode potential, the pH value, the component, and the concentration of running buffer, the separation voltage, and the injection time on CZE-AD. Then, under the optimum conditions, the six NAAs could be completely separated in 30 min and had well-shaped AD responses at 0.75 V (versus SCE) on a copper electrode. The linear calibration range of NAAs was from 5 × 10−4 to 5 × 10−6 mol L−1 with the limits of detection (LODs) ranging from 10−6 to 10−7 mol L−1 (signal-to-noise ratio = 3), and the relative standard deviations (RSDs) of the migration time and peak area were 0.45–0.55 and 3.8–6.3 %, respectively. Moreover, this method has succeeded in human serum analysis, and the determined contents of the six NAAs in human serum were in an average recovery range of 85.3–117.9 %, which confirmed the validity and practicability of this method.

Analysis of the neutral sugars of Asparagus officinalis Linn. polysaccharide by different methods has yielded inconsistent results. In the work discussed in this paper, capillary zone electrophoresis with amperometric detection (CZE–AD) was used for analysis of neutral sugars in A. officinalis Linn. polysaccharide. The configuration of the wall-jet and the diameter of the copper disk electrode were investigated to achieve optimized detection sensitivity. The separation electrolyte, separation voltage, and injection time were studied for their effects on CZE separation. Under the optimum CZE–AD conditions, seven monosaccharides were separated to baseline by using 120 mM NaOH as separation electrolyte. Linear response was excellent and repeatability was satisfactory. It was found that Asparagus polysaccharide was composed of fucose, galactose, glucose, rhamnose, arabinose, fructose, and xylose at a mole ratio of 0.2:16.2:5.0:1.0:15.5:0.6:18.8. Compared with other methods, analysis of the composition of Asparagus polysaccharide by CZE–AD had the merits of rapidness, accuracy, and lower sampling volume.

A simple and effective capillary electrophoresis–chemiluminescence (CE–CL) detection system was developed based on an ultra-fast bis(2,4,6-trichlorophenyl)oxalate (TCPO) chemiluminescence (CL) reaction (0.6 s duration) that avoided overlapping peaks and peak tailing. Through a series of static injection experiments, this unusually rapid CL reaction was ascribed to the catalytic effect of imidazole in the tetrahydrofuran solvent, which has been rarely utilized in such investigations. A possible mechanism is given to explain the results. Under the optimized conditions, rhodamine 6 G (R6G) and its hydrolysis product (R6G-COOH) could be efficiently separated through electrophoresis in 7 min, with sensitive CL detection in the proposed CE–CL system. In this way, the alkaline hydrolysis of R6G was monitored, followed by estimation of relative rate constants and activation energy. This finding and application should be helpful in further study for the TCPO CL reaction, and revealed an attractive opportunity for simplifying the CE–CL system, such as in a microchip device. Copyright © 2011 John Wiley & Sons, Ltd.

The composition of laminarin was firstly determined by analyzing its hydrolysis monosaccharides with capillary zone electrophoresis-amperometric detection (CZE-AD). Under the selected optimum conditions, fucose, galactose, glucose, mannose and xylose, which are hydrolysis products of laminarin, could be perfectly separated within 20 min and showed significant current responses at copper electrodes. The linear ranges of fucose, galactose and glucose were from 1.0 ± 10–6 to 2.0 ± 10–4 mol ± L−1, those of mannose and xylose were from 5.0 ± 10–6 to 2.0 ± 10–4 mol ± L−1, and their detection limits were at 10–7mol ± L−1 level (S/N = 3). The molar ratio of fucose, galactose, glucose, mannose and xylose in laminarin was 10.5: 2.8:1.0:7.3: 3.4 and the purity of this polysaccharide leached by the introduced leaching method was 95.7%. Compared to usual UV-vis and other spectrometric methods, analyzing polysaccharide by this method has some merits of quickness, low-volume sampling, simple instrumentation, high sensitivity and high reproducibility.

A composite electrode was fabricated from Cu2O powder, carboxyl-functionalized multi-wall carbon nanotubes (MWCNT-COOH), and paraffin oil in the proportions 51:17:32 (w/w). This composite electrode was used for amperometric detection (CZE–AD) in simultaneous capillary zone electrophoretic analysis of chlorogenic acid, rutin, sucrose, glucose, mannose, and fructose in tobacco samples. Under the optimum conditions, the six analytes could be separated in 100 mmol L−1 NaOH buffer within 30 min. Good linearity was achieved in the range 1 × 10−7–1 × 10−4 mol L−1 for the two polyphenols and 5 × 10−6–1 × 10−3 mol L−1 for the four sugars. The detection limits (S/N = 3) for the polyphenols and sugars were as low as 10−8 mol L−1 and 10−6 mol L−1, respectively.

In the paper, a new kind of vitamin B 12 (acquo-cobalamine) chemically modified electrode was fabricated and applied in capillary zone electrophoresis coupled with amperometric detection (CZE-AD) for simultaneous determination of six antioxidants in fruits and vegetables. The catalytic electrochemical properties of the chemically modified electrode could obviously enhance oxidation peak heights responses by about five times to glutathione, ascorbic acid, vanillic acid, chlorogenic acid, salicylic acid, and caffeic acid compared with common carbon disk electrode. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Under the optimum conditions, the six analytes could be completely separated and detected in a borate–phosphate buffer (pH 8.4) within 15 min. Their linear ranges were from 2.5 × 10 −7 to 1.0 × 10 −4 mol L −1 and the detection limits were as low as 10 −8 mol L −1 magnitude ( S / N = 3). The proposed method has been successfully employed to monitor the six analytes in practical samples with recoveries in the range 96.0–106.0% and RSDs less than 5.0%. Above results demonstrate that capillary zone electrophoresis coupled with electrochemical detection using vitamin B 12 modified electrode as detector is of convenient preparation, high sensitivity, good repeatability, and could be used in the rapid determination of practical samples.

Kaempferol, apigenin, rutin, quercetin, luteolin and ferulic acid are separated and detected in Chinese herbal tea using capillary zone electrophoresis coupled to amperometric detection. The phosphate running buffer also contains s-cyclodextrin (s-CD), which assists in separation and gives excellent separations within 20 min and detection limits as low as 10 ng mL−1 (S/N = 3). The effects of working electrode potential, pH and concentration of running buffer, concentration of s-CD, separation voltage and injection time were investigated. The method was applied to analyze tea samples with recoveries in the range of 90.0 to 107.0%. The method offers high separation efficiency, short analysis time, small sample consumption, and good repeatability.

In general capillary zone electrophoresis (CZE) separation models, o-, m-, and p-phenylenediamine isomers can be separated in a weak acidic running buffer for their pK(a) values being 4.52, 5.64, 6.04, respectively, while o-, m-, and p-dihydroxybenzene isomers can be separated in a weak basic buffer for their pK(a) values being 9.40, 9.40 and 10.04, respectively. So, it is hard to find a suitable running buffer at a fixed pH in normal CZE for simultaneous separation of these two groups of positional isomers. In this paper, a novel method based on alternately running two different pH buffers in CZE coupled with amperometric detection (CZE-AD) was designed to simultaneously determine these two groups of positional isomers. It is found that when two different pH running buffers were employed alternately under appropriate order and time, the six analytes could be separated perfectly in less than 20 min and the detection limits were as low as 10(-7) mol/L. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Experimental results demonstrated that the introduced method was practical to simultaneously determine two groups of positional isomers with different pK(a) and had some advantages of high sensitivity, good repeatability and small sample requirement.

An effective method for selective immobilization of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+ ) onto one target electrode surface based on the electrodeposition of RuDS NPs (Ru(bpy) 3 2+ doped silica nanoparticles)/chitosan composite film is presented in this paper. Ru(bpy) 3 2+ was selectively deposited onto four individual electrodes in an Au electrode array. The results demonstrate the possibility of selective immobilization of Ru(bpy) 3 2+ onto array electrodes and selective immobilization of different ECL composite. Therefore have potential applications in bioanalysis, capillary electrophoresis and drug screening. RuDS NPs and the resulting composite film were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM) and Field emission-scanning electron microscope (FE-SEM). The electrochemiluminescence (ECL) sensor based on the composite film modified electrode exhibited excellent reproducibility, stability and sensitivity for the detection of tri-n-propylamine (TPA). The linear range was from 1 × 10 −10 to 1 × 10 −6 M ( R 2 = 0.9954) with the detection limit of 5 × 10 −11 M.

The major bioactive components in a Chinese herb named Polygonum perfoliatum L. including ferulic acid, vanillic acid, quercetin, caffeic acid and protocatechuic acid were simultaneously determined by capillary electrophoresis with electrochemical detection (CE-ED) in this paper. The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CE-ED were investigated. Under the optimum conditions, the five analytes could be separated within 17 min at a separation voltage of 18 kV in 10 mmol· L−1 phosphate buffer (pH 9.2). A 300 µm diameter carbon disk electrode generated good responses at +0.95 V (vs. SCE) to the five analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 7.1×10−8 to 9.3×10−8 g·mL−1 for the analytes. This proposed method could be successfully applied to the analysis of the real samples with relatively simple extraction procedures and satisfactory results.

A carbon paste electrode modified with multiwall carbon nanotubes and copper(I) oxide (MWCNT–Cu2O CPME) was fabricated, and the electrochemical behaviors of 19 kinds of natural amino acids at this modified electrode were studied. The experimental results showed that the various kinds of amino acids without any derivatization displayed obvious oxidation current responses at the modified electrode. It was also found that the current response values of amino acids were dependent mainly on pH values of buffer solutions. The phenomenon could be explained by the fact that the amino acids suffered complexation or electrocatalytic oxidation processes under different pH values. Six kinds of amino acids (arginine, tryptophan, histidine, threonine, serine, and tyrosine), which performed high-oxidation current responses in alkaline buffers, were selected to be detected simultaneously by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). These amino acids could be perfectly separated within 20 min, and their detection limits were as low as 10−7 or 10−8 mol L−1 magnitude (signal/noise ratio = 3). The above results demonstrated that MWCNT–Cu2O CPME could be successfully employed as an electrochemical sensor for amino acids with some advantages of convenient preparation, high sensitivity, and good repeatability.

Despite the separation efficiency of capillary electrophoresis (CE) is much higher than other chromatographic methods, it is sometimes difficult to perfectly separate the complex ingredients in biological samples. One possible and simple way to develop the separation effect in CE is to add some modifiers in the running buffer. In this paper, the suitable running buffer modifiers were explored to simultaneously separate and detect six typical flavonoids (apigenin, luteolin, kaempferol, quercetin, (+)-catechin and (-)-epicatechin) which are the main active ingredients in chrysanthemum by capillary zone electrophoresis with amperometric detection (CZE-AD). It was found that when beta-cyclodextrin (beta-CD) and the mixture of methanol and ethanol were used as running buffer modifiers, a baseline separation of the six analytes could be accomplished in less than 20 min and the detection limits were as low as 10(-7) or 10(-8)gm l(-1). Other factors affecting the CZE separation, such as working potential, pH value and ionic strength of running buffer, separation voltage and sample injection time were extensively investigated. Under the optimum conditions, a successful practical application on the determination of chrysanthemum samples confirmed the validity and practicability of this method.

In this paper, four trace ingredients (rutin, gallic acid, quercetin, chlorogenic acid) in green tea were simultaneously determined by capillary electrophoresis coupled with amperometric detection (CE-AD). Effects of several important factors such as the pH and concentration of running buffer, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. Under the optimum conditions, the analytes could be separated within 20 min at a separation voltage of 18 kV in a 60 mmol/L borate buffer (pH 8.7). A 300 µm diameter carbon disk electrode generated good responses at 950 mV (vs. SCE) for all analytes. The relationship between the peak currents and concentrations of the analytes was linear over about three orders of magnitude with detection limits (S/N=3) ranging from 1.0×10−7 to 1.0×10−4 g·mL−1 for all the analytes. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations less than 3% for both migration time and peak current (n=7), which could be successfully used for the determination of the analytes in green tea with satisfactory assay results.

In this paper, a nano-NiO modified carbon paste electrode in capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the determination of carbohydrates. Effects of several important factors such as detection potential, the concentration of running buffer, separation voltage and injection time were investigated to acquire the optimum conditions. Under the selected optimum conditions, three carbohydrates: glucose, sucrose and fructose could be perfectly separated within 20 min. The relationships between peak current and concentration of three carbohydrates were linear over about 3 orders of magnitude with detection limits (S/N = 3) ranging from 3.0 × 10 −7 to 6.0 × 10 −7 mol L −1 . The electrode was stable, and can be used for at least one week. The proposed method has been successfully applied to monitor carbohydrates in the real samples with satisfactory assay results.

In this paper, a polyamide-modified carbon paste electrode in capillary zone electrophoresis with amperometric detection (CZE–AD) was firstly applied to the determination of four carbamate pesticides: fenobucarb, isoprocarb, metolcarb and carbaryl. The four carbamates were hydrolyzed in alkalescent aqueous solutions, resulting in the formation of 2-sec-butylphenol, 2-isopropylphenol, m-cresol and α-naphthol, which could be determined by amperometry after capillary electrophoretic separation. Under the selected optimum conditions, the four analytes could be perfectly separated within 23 min. The linear ranges of 2-sec-butylphenol, 2-isopropylphenol and m-cresol were from 1.0 × 10 −7 to 2.0 × 10 −5 mol L −1 and that of α-naphthol was from 2.0 × 10 −7 to 2.0 × 10 −5 mol L −1 and their detection limits were 3.0 × 10 −8 , 3.0 × 10 −8 , 3.0 × 10 −8 and 6.0 × 10 −8 mol L −1 , respectively ( S / N = 3). Fenobucarb, isoprocarb, metolcarb and carbaryl can be indirectly determined by this CZE–AD method with recovery of 105, 104, 110 and 98% and R.S.D. of 4, 3, 4 and 3%, respectively. Above results demonstrated that this method was of high sensitivity, good repeatability and could be used in the rapid determination of the pesticide residues.

A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, emodin, syringic acid, vanillic acid, rhein, and protocatechuic acid in Spatholobus suberectus dunn and its medicinal preparations for the first time. The effects of a working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CE‐ED were investigated. Under the optimum conditions, the analytes could be separated in a 60 mmol L−1 borate buffer (pH 9.0) within 26 min. A 300 µm diameter carbon disk electrode has a good response at +0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 5×10−8 g mL−1 to 2×10−7 g mL−1 for the analytes. The method has been successfully applied to the analysis of a real sample, with satisfactory results.

A method based on capillary electrophoresis with electrochemical detection (CE‐ED) has been developed for the first time for the separation and determination of isovanillic acid, vanillic acid, quercetin, rosmarinic acid, caffeic acid, and protocatechuic acid in Origanum vulgare L. and its medicinal preparations. The effects of working electrode potential, pH level, concentration of running buffer, separation voltage, and injection time on CE‐ED were investigated. Under the optimum conditions, the analytes could be separated in a 50 mmol L−1 borate buffer (pH 8.7) within 21 min. A 300‐µm diameter carbon disk electrode has a good response at +0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 4×10−8 g mL−1 to 2×10−7 g mL−1 for the analytes. The method has been successfully applied to the analysis of real sample, with satisfactory results.

A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, kaempferol, chlorogenic acid, 4-hydroxybenzoic acid, quercetin and protocatechuic acid in hawthorn for the first time. The effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CE-ED were investigated. Under the optimum conditions, the analytes could be separated in a 60 mmol·L−1 borate buffer (pH 8.7) within 21 min. A 300 μm diameter carbon disk electrode has a good response at +0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 3×10−8 to 2×10−7 g·mL−1 for the analytes. The method has been successfully applied to the analysis of real sample, with satisfactory results.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), has been developed for simultaneous determination of four active ingredients in Vc Yinqiao tablets including paracetamol, vitamin C, caffeic acid and chlorogenic acid. A carbon-disk electrode was used as working electrode and 0.95 V (versus SCE) was selected as detection potential. The optimal conditions of CZE experiment were 30 mmol·L−1 borate solution (pH 9.5) as running buffer, 14 kV as separation voltage and 8 s (14 kV) as electro-kinetic sampling time. Under the selected optimum conditions, paracetamol, vitamin C, caffeic acid and chlorogenic acid could be perfectly separated within 22 min, and their detection limits (S/N=3) ranged from 5×10−7 to1×10−6 mol·L−1. This proposed method demonstrated good reproducibility with relative standard deviations of less than 3% for both migration time and peak current (n=7). The utility of this method was demonstrated by monitoring a kind of compound medicine named Vc Yinqiao tablets and the assay results were satisfactory.

A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, isovanillic acid, vanillic acid and myricetin in Dioscorea bulbifera L. and its medicinal preparations. The effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time were investigated. Under optimum conditions, the analytes could be separated in a 40 mmol L−1 borate buffer (pH 8.7) within 15 min. A 300 μm diameter carbon disk electrode has a good response at + 0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N = 3) ranging from 3.0 × 10−8 g mL−1 to 1.0 × 10−7 g mL−1. The method has been successfully applied to the analysis of real samples.

In this paper, capillary zone electrophoresis with amperometric detection (CZE–AD) was firstly applied to the simultaneous separation and determination of nitroaniline positional isomers. The three analytes could be perfectly analyzed by using the buffer of extreme pH. The effects of several important factors were investigated to find optimum conditions. A carbon-disk electrode was used as working electrode. The optimal conditions were 40 mmol/L tartaric acid–sodium tartrate (pH 1.2) as running buffer, 17 kV as separation voltage and 1.10 V (versus saturated calomel reference electrode, SCE) as detection potential. Under the optimum conditions, o-, m- and p-nitroaniline were separated successfully and good linearity, reproducibility and recovery results were obtained. The detection limit for m-nitroaniline was as low as at 9.06 × 10−9 mol/L. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 1.8% for migration time and 1.1% for peak areas. The utility of this method was demonstrated by monitoring dyestuff wastewater and the assay results were satisfactory.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), was developed for simultaneous determination of 3-amino-3-azabicyclo[3,3,0]octane (aminoheterocycle) and 3-azabicyclo[3,3,0]octane (azabicycle) in gliclazide bulk drug. The optimal conditions of CZE-AD were 50 mM borate solution (pH 9.0) as running buffer, 14 kV as separation voltage and 0.95 V (versus SCE) as detection potential. Under the selected optimum conditions, the two analytes could be perfectly separated within 9 min. The linearity range of aminoheterocycle was from 1.0 × 10 −6 to 1.0 × 10 −3 M and that of azabicycle was from 2.0 × 10 −6 to 1.0 × 10 −3 M. Their detection limits were 5.0 × 10 −7 and 1.0 × 10 −6 M, respectively, (S/N = 3). This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 2% for both migration time and peak current. It has been successively used for the determination of these two analytes in gliclazide bulk drug, and the assay results were satisfactory.

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE-AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L(-1) phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L(-1)) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4 x 10(-2) to 2.2 microg mL(-1) for LDME, 2.9 x 10(-1) to 49.5 microg mL(-1) for L-DOPA, and 1.4 x 10(-2) to 1.5 microg mL(-1) for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL(-1), respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.

A novel method, capillary electrophoresis with amperometric detection, has been established for rapid and effective measurement of levodopa (L-dopa), and benserazide (BS) and its impurity (R,S)-2-amino-3-hydroxypropanohydrazide (Ro-04-1419) in co-beneldopa pharmaceutical formulations. Suitable separation and amperometric detection conditions were investigated and optimized. The optimum conditions of CZE detection were 40 mm phosphate solution at pH 5.3 as running buffer, 17 kV separation voltage, carbon-disk working electrode, 0.95 V (relative to Ag/AgCl) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 1.25 to 50 μg mL−1 for L-dopa, 1.2 × 10−1 to 25.5 μg mL−1 for BS, and 1.0 × 10−2 to 4.4 × 10−1 μg mL−1 for Ro-04-1419, with correlation coefficients of 0.9994, 0.9951, and 0.9933, respectively. The detection limits for L-dopa, BS, and Ro-04-1419 were 0.38, 0.02, and 0.004 μg mL−1, respectively. Average recoveries were 100.2% for L-dopa, 102.4% for BS, and 90.8% for Ro-04-1419. This method was successfully applied to co-beneldopa granules and tablets.

A simple, reliable and reproducible method was developed for determination of psoralen and isopsoralen in several traditional Chinese medicines, such as Shouwu Pian, Gubenkechuan Pian, was described in this paper. It was based on capillary zone electrophoresis with amperometric detection (CZE-AD). A carbon-disc electrode was used as working electrode. The optimal conditions of separation and detection were pH7.6 phosphate buffer (20 mM), 20 kV for the separation voltage and 1.00V (vs. Ag/AgCl) for the detection potential. The linear ranges were 6.90 × 10-5~1.30 × 10-7 mol L-1for psoralen and 5.0 × 10-5~1.80 × 10-7 mol·L-1 for isopsoralen with the correlation coefficient of 0.9984 and 0.9994, respectively. The detection limits for psoralen and isopsoralen were 4.2 × 10-8 mol·L-1 and 6.0 × 10-8 mol·L-1 based on the signal to noise ratio of 3. The method built in this paper was directly applied to the determination of several traditional Chinese medicines with some simple pretreatment. The assay result was satisfactory.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), has been developed for simultaneous determination of five active ingredients in complicated traditional Chinese medicines including chlorogenic acid, caffeic acid, aloe-emodin, emodin and rhein. A carbon-disk electrode was used as working electrode. The optimal conditions of CZE detection were 30 mM borate solution (pH 9.5) as running buffer, 18 kV as separation voltage and 1.00 V (versus Ag/AgCl) as detection potential. There was excellent linearity between current response and analyte concentration over two orders of magnitude, while the limits of detection were 1.1 x 10(-7), 3.0 x 10(-7), 1.5 x 10(-7), 2.9 x 10(-7), 1.4 x 10(-6) mol/l for aloe-emodin, emodin, rhein, chlorogenic acid and caffeic acid, respectively (S/N = 3). The utility of this method was demonstrated by monitoring a kind of complicated Chinese medicine named Huangdan Yinchen Keli. Two samples manufactured by different companies were monitored with satisfactory results.

A method based on capillary electrophoresis (CE) with electrochemical detection (ED) was developed for the determination of taurine in Lycium Barbarum L., LIPOVIYAN beverage and milk powder. The effects of some important factors such as the acidity of the running buffer, separation voltage, injection time, and applied potential to working electrode were investigated. Operated in a wall-jet configuration, a 300 μm diameter carbon-disk electrode was used as the working electrode, which exhibits good responses at +1.05 V (vs. SCE) for taurine. Excellent linearity was obtained in the concentration range from 5.0×10−4 mol/L to 5.0×10−6 mol/L. The detection limit (S/N=3) was 1.0×10−7 mol/L. This proposed method has been successfully applied to analyze the actual samples with satisfactory assay results.

Besides the running buffer, pH of buffer, separation voltage and sampling time, the diluting agent was studied in this paper as one of the important factors influencing the sensitivity in capillary electrophoresis (CE) with amperometric detection (AD) when electrokinectic sampling was used. Clonidine hydrochloride, hydrochlorothiazide and rutin, which are positively charged, neutral and negatively charged, respectively, in aqueous solutions, could be perfectly separated by CE with 25 mmol x L(-1) Na(2)B(4)O(7) - 50 mmol x L(-1) NaH(2)PO(4) as running buffer and detected by measuring their current responses with AD. Before CE running, some kinds of diluents including water, methanol, formamide, running buffer, hydrochloric acid and sodium hydroxide were, respectively, applied to dilute the stock solutions of above three analytes and their effects on the sensitivity of CE-AD were investigated. The results showed that for electrokinetic injection, the current responses of these three analytes were greatly affected in different ways when different diluting agents were used. This method was applied to simultaneously determine the active ingredients in one Chinese compound hypotensor named Zhen Ju Jiang Ya Pian, in which the contents of clonidine hydrochloride, hydrochlorothiazide and rutin is very different as 0.03 mg : 5 mg : 20 mg per tablet, and satisfactory results were obtained by adjusting their sensitivity by selecting the suitable diluting agent.

Although daunorubicin, pharmorubicin and idarubicin are important drugs in medical and in pharmaceutical research, the dissociation constants ( K a ) of these substances are frequently not known. A method based on a non-linear model enabling the efficient determination of the K a of the three drugs by capillary zone electrophoresis with amperometric detection (CZE-AD) has been demonstrated. The p K a values obtained through the method were in agreement with the values by typical spectrophotometric method.

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the simultaneous determination of rutin (RT) and hydrochlorothiazide (HCT) in compound Chinese herb medicines and human urine samples. The two analytes could be perfectly analyzed within 12 min and showed significant current responses at carbon electrode under the optimum conditions. It was found that the linear range of HCT was from 2.0 x 10(-6) to 1.0 x 10(-4) mol l(-1) and that of RT was from 1.0 x 10(-6) to 1.0 x 10(-4) mol l(-1). Their sensitivity was determined by linear regression and calculated as 7.02 x 10(4) and 2.17 x 10(5) nA l mol(-1), respectively, and their detection limits were 5.0 x 10(-7) and 2.0 x 10(-7) mol l(-1), respectively (S/N=3). Above results demonstrated that this method was of high sensitivity, good repeatability, high selectivity and could be used in metabolic kinetics studies of medicines. Satisfactory results were obtained when this method was used to simultaneously analyze the amounts of RT and HCT in one general compound Chinese herb medicine-Zhen Ju jiang Ya Pian and human urine samples.

A high-performance capillary electrophoretic (CE) method with electrochemical detection (ED) has been developed for determination of the pharmacologically active flavonoids in Ginkgo biloba L. and phytopharmaceuticals containing its extract. Epicatechin, catechin, rutin, apigenin, luteolin, and quercetin are important flavonoids in this plant. Operated in a wall-jet configuration, a 300 micro m diameter carbon-disk electrode was used as working electrode with good response to the six analytes at +1000 mV (relative to the SCE). Under the optimum conditions, the analytes were separated within 22 min in a borax buffer (pH 9.0). Excellent linearity was obtained over two orders of magnitude and detection limits (S/N=3) ranged from 1.4 x 10(-7) to 5.0 x 10(-7) g mL(-1) for all six analytes. The method was successfully used for assay of Ginkgo biloba L. and its phytopharmaceuticals after a relatively simple extraction procedure; the results obtained were satisfactory.

A simple, reliable and reproducible method, based on capillary electrophoresis (CE) with electrochemical detection (ED), for the determination of three active ingredients of both Apocynum Venetum compound tablets and medicinal herbs was described. The active ingredients mainly consist of rutin, d-catechin and quercetin. Operated in a wall-jet configuration, a 300 μm diameter carbon-disk electrode was used as the working electrode, which exhibits good responses at + 950 mV (vs. SCE) for the three analytes. Under the optimum conditions, the analytes were base-line separated within 19 min, and excellent linearity was obtained in the concentration range from 1.0 × 10−4 g/ml to 1.0 × 10−6 g/ml. The detection limit (S/N = 3) was 3.0 × 10−7 g/ml, 5.0 × 10−7 g/ml, and 4.0 × 10−7 g/ml for d-catechin, rutin and quercetin, respectively. This work provides a useful method for the analysis of traditional Chinese medicines.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection, for separation and determination of β-agonists, namely adrenaline, salbutamol and salmeterol in serum was described in this paper. A carbon-disk electrode was used as working electrode. The optimal conditions of separation and detection were pH 6.6 phosphate buffer solution (0.06 mol/l), 12 kV for the separation voltage and 0.85 V (versus Ag/AgCl) for the detection potential. The linear ranges were from 1.0×10 −7 to 1.0×10 −5 mol/l for adrenaline, 3.0×10 −7 to 5.0×10 −5 mol/l for salbutamol, and 5.0×10 −7 to 8.0×10 −5 mol/l for salmeterol with the correlation coefficient of 0.998, 0.998 and 0.992, respectively. The detection limits for adrenaline, salbutamol, and salmeterol were 5.0×10 −8 , 2.0×10 −7 and 2.0×10 −7 mol/l (based on the signal to noise ratio of 3). The method built in this paper was directly applied to the determination of β-agonists in the spiked serum without any other sample pre-treatment except filtration, and the assay results were satisfactory.

A simple, reliable and reproducible method for separation and determination of levodopa and carbidopa based on capillary electrophoresis with amperometric detection is described in this paper. A potential of 900 mV (versus Ag/AgCl 3 mol/l KCl) was applied to the carbon disk electrode, which was used as working electrode in this system. Under the optimum conditions, two analytes were separated completely within 12 min, with linear ranges of 1.2–100.0 and 1.2–150.0 μg/ml, and detection limits of 0.6 and 0.3 μg/ml for levodopa and carbidopa, respectively. The mean recoveries of levodopa and carbidopa were 97.4 and 102.3%. The method was applied successfully to the determination in the real pharmaceutical samples.

A simple, rapid and specific capillary electrophoresis (CE) method has been developed for the separation and determination of pseudoephedrine hydrochloride (PSED), paracetamol (PRCT) and dextromethorphan hydrochloride (DEMP) with UV detection. The CE was performed in 20 mmol/l sodium phosphate buffer solution (pH 7.0). The three ingredients were completely separated within 5 min, and quantified with an UV-detector at 200 nm. Relative standard deviations of 0.85% for PSED, 3.90% for PRCT and 0.84% for DEMP were achieved for seven injections of the sample containing about PSED of 30 μg/ml, PRCT of 325 μg/ml and DEMP of 15 μg/ml. The excellent linearity was obtained in the concentration range 300.0–2.5 μg/ml for PSED, 500.0–5.0 μg/m for PRCT and 500.0–10.0 μg/m for DEMP. The detection limits for PSED, PRCT and DEMP were 0.75, 1.20 and 2.50 μg/ml, respectively. The proposed method has been applied to the monitoring of commercial composite pseudoethedrine tablets and biological sample (urine). The analytical results were satisfactory.

The amperometric detection (AD) employing a carbon disk electrode as a working electrode to determine the thiol compounds, including cysteine (CYS), glutathione (GSH), 6-thiopurine (TP), and methimazole (MMI), following their separation by capillary zone electrophoresis (CZE) is described in this paper. The detection potential was chosen at +1100 mV and all analytes exhibit good response at this potential on the carbon disk electrode. The reproducibility, linearity, and recovery were evaluated under the optimum conditions. The four analytes can be baseline resolved within 20 min and the detection limits reached about 10(-6) mol/l of magnitude. The method was applied to the separation and determination of the actual thiol samples and the analytical results were satisfactory.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection, for the determination of daunorubicin in human urine is described in this paper. A carbon disk electrode used as working electrode. The optimal conditions of separation and detection were pH 7.8 phosphate buffer (0.15 mol/l), 8 kV for the separation voltage and 0.95 V (versus Ag/AgCl, 3 mol/l KCl) for the detection potential. The linear range was from 2×10 −6 to 2×10 −4 mol/l with the regression coefficient of 0.9995, and the detection limit was 8×10 −7 mol/l. The method built in this paper was directly applied to the determination of daunorubicin in the imitation human urine without any other sample pre-treatment except filtration, and the assay result was satisfactory.

Co-electroosmotic capillary electrophoresis with amperometric detection at a Cobalt phthalocyanine (CoPC) modified carbon paste electrode was evaluated for the determination of oxalic acid in urine. The running buffer consisted of 10 mM phosphate (pH=5.70) and 0.25 mM Cetyltrimethylammonium bromide. Under the optimum conditions, a detection limit of 0.12 μM was achieved for oxalic acid. The response was linear between 0.5 and 1000 μM with a correlation coefficient of 0.9995. Applications of the method to real urine samples were described.

A co-electroosmotic capillary electrophoretic (CE) system with amperometric detection (AD) was used for the simultaneous determination of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP). The optimum electrolyte consisted of 0.02 M phosphate adjusted to pH 5.40 and 0.15 mM cetyltrimethylammonium bromide (CTAB). Baseline separation was obtained within 21 min. Using a carbon fiber disc electrode at a potential of +1.20 V (vs. Ag/AgCl), a good linear relation between peak current and concentration for each analyte was obtained in the range of 5 ∼ 150 μg/ml. For the studied system, the precisions of migration time and peak current (in terms of relative standard deviation, n = 5) were in the range of 1.5 ∼ 1.8% and 2.0 ∼ 3.1%, respectively. The method was demonstrated by analyzing ATP, ADP and AMP in real medicinal tablets.

The amperometric detection of chloramphenicol and its hydrolytic product, 2-amino-1-(4-nitrophenyl)-propane-1,3-diol, following their separation by capillary zone electrophoresis is described in this paper. A carbon disk electrode used as working electrode for two analytes exhibits good response at +1175 mV (vs. Ag/AgCl). The method was validated, and reproducibility, linearity, and recovery for both components was assessed. Under the optimum conditions, the two analytes were baseline resolved within approximately 11 min. The limits of detection were 0.5 and 0.2 μg/ml for chloramphenicol and its hydrolysate, respectively. The method was successfully applied to analyze the stability of four batches of chloramphenicol ophthalmic solutions stored at room temperature. The suggested procedure was found to have a high accuracy and was less time-consuming.

A graphite electrode modified with a thin film of mixed-valent ruthenium-iron cyanide was prepared and evaluated as an amperometric sensor for nonelectroactive cations in capillary electrophoresis. This electrode was very stable and showed a selective and sensitive response to Cs+. Based on three times signal-to-noise ratio, a detection limit of 2×10−8 M for Cs+ was obtained under the optimized conditions. The applicability of this method was demonstrated for the analysis of synthetically constituted and real samples.

A simple, reliable and reproducible method, based on capillary electrophoresis with amperometric detection, for separation and determination of the active ingredients in tablets of the composite sulphonamides is described in this paper. A carbon-disc electrode used as working electrode for three analytes exhibits good responses at +1275 mV (vs. Ag/AgCl). Under the optimum conditions, three analytes were base-line separated, and excellent linearity was obtained in the concentration range from 3.0×10 −6 to 5.0×10 −4 mol/l. The detection limit was 1.0×10 −6 , 1.0×10 −6 , and 8.0×10 −7 mol/l for sulphadiazine, sulphamethazine and trimethoprim, respectively. This method was successfully used in the analysis of actual pharmaceutical samples, and the assay results were satisfactory.

The simultaneous determination of four active ingredients in Nao Xue Shuan Tablets, including ferulic acid, protocatechuic aldehyde, caffeic acid and protocatechuic acid was performed by capillary zone electrophoresis with amperometric detection (CZE-AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Under the optimum conditions, the four analytes could be perfectly separated within 18 min. A 300 μm diameter carbon-disc electrode had a good response at +0.95 V (vs. SCE) for the four analytes. The response was linear over three orders of magnitude with detection limits (S/N = 3) as low as 10 −8 or 10 −9 g/mL for the analytes. The assay results were satisfactory with recoveries in the range of 85.2–93.0% and RSDs less than 3.3%.

A novel approach to the simultaneous determination of sugars and organic acids by co-electroosmotic capillary electrophoresis with amperometric detection at a disk-shaped electrode was developed. The addition of cetryltrimetylammonium bromide (CTAB) to the carrier electrolyte not only established the co-electroosmotic conditions but also increased the detection sensitivity of the analytes studied. In the optimum carrier electrolyte system composed of 0.05 M NaOH and 0.20 mM CTAB, the simultaneous determination of tartaric acid, ascorbic acid, fructose, glucose, and sucrose can be accomplished within 14 min with precisions (RSD) less than 5% for peak height and 1.5% for migration time at the concentration level of 5×10−4 M. The present method was successfully applied to the analysis of grape samples with recoveries in the range 95.0–103.0%.

The enantiomers of two amine derivatives were directly separated by capillary electrophoresis (CE), employing β-cyclodxtrin (β-CD) as a chiral additive in strongly alkaline solutions. The analytes were detected by electrochemistry, using a copper disk electrode at +675 mV vs Ag/AgCl reference electrode. Both the free enantiomers and the enantiomer-cyclodxtrin inclusion complexes could be detected using this approach, although the complexed forms gave lower oxidation currents than the free forms. Factors affecting the chiral CE separation of the analytes, such as working potential, concentration of running buffer and β-CD, and applied voltage, were extensively investigated. Under the optimum conditions, baseline separation of the enantiomers could be accomplished in less than 18 min. In addition, a successful application of the method to the enantiomeric purity determination confirmed its validity and practicability.

A simple method allowing the efficient separation and determination of cyclodextrins (CDs) by capillary electrophoresis (CE) with amperometric detection was demonstrated. Three native CDs, α-, β- and γ-CD, were baseline separated within 22 min and their detection limits were determined to be 2.0, 1.6 and 1.0 μM, respectively, under the optimum conditions. Mono-2-O-hydroxypropyl-β-CD and β-CD, which could not be baseline separated under the conditions used to separate the native CDs, were completely separated when sodium toluene-p-sulfonate was added into the running buffer.

Capillary electrophoresis was first employed for the determination of pKa values of 6 aldohexose isomers based on their differential migrations within the capillary tubing. The pKa values obtained were found to be independent of the separation voltages. The quantitative basis of pKa determination was also discussed.