Capillary electrophoresis with amperometric detection of curcumin in Chinese herbal medicine pretreated by solid-phase extraction

In the present study, curcumin from Chinese herbal medicine turmeric was determined by capillary electrophoresis with amperometric detection (CE-AD) pretreated by a self-designed, simple, inexpensive solid-phase extraction (SPE) cartridge based on the material of tributyl phosphate resin. An average concentration factor of 9 with the recovery of >80% was achieved when applied to the analysis of curcumin in extracts of turmeric. Under the optimized CE-AD conditions: a running buffer composed of 15 mM phosphate buffer at a pH 9.7, separation voltage at 16 W, injection for 6 s at 9 W and detection at 1.20 V, CE-AD with SPE exhibited low detection limit as 3 - 10(-8) mol/l (SIN = 3), high efficiency of 1.0(.)10(5) N, linear range of 7(.)10(-4) -3(.)10(-6) mol/l (r = 0.9986) for curcumin extracted from light petroleum. The method developed resulted in enhancement of the detection sensitivity and reduction of interference from sample matrix in complicated samples and exhibited the potential application for routine analysis, especially in food, because a relatively complete process of sample treatment and analysis was described.

Determination of sulpiride by capillary electrophoresis with end-column electrogenerated chemiluminescence detection

Background: Capillary electrophoresis (CE) with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)]-electro-generated chemiluminescence (ECL) detection is a promising method for clinical analysis. In this study, a method combining CE with Ru(bpy)(3)(2+) ECL (CE-ECL) detection that can be applied to amine-containing clinical species was developed, and the performance of CE-ECL as a quantitative method for determination of sulpiride in human plasma or urine was evaluated. Methods: Sulpiride was separated by capillary zone electrophoresis in uncoated fused-silica capillaries [510 cm x 25 mum (i.d.)] filled with phosphate buffer (pH 8.0 and a driving voltage of +15 kV, with end-column Ru(bpy)(3)(2+) ECL detection. A platinum disc electrode was used as working electrode. Sulpiride in human plasma or urine samples (100 muL) was extracted by a double-step liquid-liquid extraction procedure, dried under nitrogen at 35 degreesC in a water bath, and reconstituted with 100 muL of filtered water. The extraction solvent was ethyl acetate-dichloromethane (5:1 by volume). Results: Under optimum conditions (pH 8.0 phosphate buffer, injection for 6 s at 10 kV, and +1.2 V as detection potential), separation of sulpiride was accomplished within 4 min. The calibration curve was linear over a concentration range of 0.05-25.0 mumol/L, and the limit of detection was 2.9 x 10(-8) mol/L for sulpiride. Intra- and interday CVs for ECL intensities were <6%. Extraction recoveries of sulpiride were 95.6-101% with CVs of 2.9-6.0%. The method was,clinically validated for patient plasma and urine samples. Conclusions: CE combined with Ru(bpy)(3)(2+) ECL is reproducible, precise, selective, and enables the analysis of sulpiride in human plasma and urine. It thus is of value for rapid and efficient analysis of amine-containing analytes of clinical interest.

A method to construct a third-generation horseradish peroxidase biosensor: Self-assembling gold nanoparticles to three-dimensional sol-gel network

A novel method for fabrication of horseradish peroxidase biosensor has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a hydrolyzed (3-mercaptopropyl)-trimethoxysilane (MPS) sol-gel solution to assemble three-dimensional silica gel, and then gold nanoparticles were chemisorbed onto the thiol groups of the sol-gel network. Finally, horseradish peroxidase (HRP) was adsorbed onto the surface of the gold nanoparticles. The distribution of gold nanoparticles and HRP was examined by atomic force microscopy (AFM). The immobilized horseradish peroxidase exhibited direct electrochemical behavior toward the reduction of hydrogen peroxide. The performance and factors influencing the performance of the resulting biosensor were studied in detail. The resulting biosensor exhibited fast amperometric response (2.5 s) to H2O2. The detection limit of the biosensor was 2.0 mumol L-1, and the linear range was from 5.0 mumol L-1 to 10.0 mmol L-1. Moreover, the studied biosensor exhibited high sensitivity, good reproducibility, and long-term stability.

Determination of ascorbic acid by flow injection chemiluminescence suppression method

chemiluminescence suppression method for the determination of ascorbic acid based on Luminol-KIO4-H2O2-ascorbic acid system was established. The linear range for ascorbic acid is 1.0 x 10(-7) similar to 1.0 x 10(-5) mol/L and the detection limit is 6.0 x 10(-8) mol/L. The relative standard deviation (n = 11) is 1.0% for 8.0 x 10(-7) mol/L ascorbic acid. The method has been used to determine the content of ascorbic acid in tablets and injections with satisfactory results.

Determination of three beta-blockers by capillary electrophoresis with end-column electrochemical detection

Three beta -blockers (propranolol, timolol, acebutolol) were separated by capillary electrophoresis (CE) and detected by end-column electrochemical detection (EC). In the present work, a carbon fiber (33 mum) electrode was used as the working electrode. The effect of the buffer concentration, buffer pH, detection potential and separation voltage on the separation of analytes and behavior of electrochemical detection was systematically investigated. The optimum conditions determined were as following: 40 cm length, 25 mum i.d. capillary; 17.5 kV separation voltage; 2 s injection at 15 kV; 70mM phosphate buffer, pH 3.5; detection potential + 1.2V (vs. Ag/AgCl). Under these conditions, the linear ranges of beta -blockers were over three orders of magnititude and the low detection limit of 10(-8)M was obtained. This method was also applied to detect the simulated urine sample.

Simultaneous determination of 2-aminothiazole, 2-aminobenzothiazole and 2-mercaptobenzothiazole by capillary electrophoresis with end-column amperometric detection

Capillary electrophoresis with amperometric detection is evaluated for the simultaneous determination of 2-aminothiazole (A), 2-amino-benzothiazole (AB), 2-mercaptobenzothiazole (AM). The cyclic voltammogram, hydrodynamic voltammogram, effect of pH, concentration of buffer and separation voltage on the separation and the detection were studied. The conditions were optimized as follows: 50 mM phosphate buffet; pH 6.0, 2s at 17.5 kV sample injection, separation at 17.5 kV, 1.2 V as detection potential. The method provided low detection limit as 0.5 mu M, 0.05 mu M and 0.01 mu M, wide linear range 2-200 mu M, 10-200 mu M and 0.025-100 mu M for A, AB, and AM, respectively. The variations in peak current and migration time for 15 consecutive injections of a standard containing 5 mu M each compound were 3.7, 2.1, and 3.9%, and 1.2, 0.8, and 1.2%, for A, AB and AM, respectively. This method was employed to analyze river water.

Determination of propranolol by capillary electrophoresis with end-column amperometric detection

A capillary electrophoresis-amperometric detection system was developed for the determination of propranolol (PRO) at a 33 mu m carbon fiber microdisk electrode (CFE). The cyclic voltammogram, the hydrodynamic voltammograms and the effect of pH were studied. Under the optimum conditions: separation Voltage 15 kV; injection 3 s at 15 kV; 10 mM pH 7.5 phosphate buffer, 1.15 V (vs. Ag/AgCl) detection potential, the detection limit (LOD) for PRO was 0.05 mu M (S/N = 3). The response for PRO was linear over two orders of magnitude with a linear correlation coefficient of 0.994. The feasibility of this method was demonstrated by the detection of PRO in urine sample.

Determination of barbituric acid and 2-thiobarbituric acid with end-column electrochemical detection by capillary electrophoresis

Capillary electrophoresis (CE) with end-column electrochemical detection (EC) of barbituric acid (BA) and 2-thiobarbituric acid (TA) has been described. Under optimum condition, BA and TA were separated satisfactorily, and a response of high sensitivity and stability was obtained at a detection potential of 1.25 V versus Ag/AgCl. Optimized end-column detection provides detection limit as low as 0.5 and 0.1 mu M for BA and TA, respectively. The calibration graph was linear over three orders of magnitude. The relative standard deviations (n = 10) of peak currents and migration times obtained for both BA and TA were 3.4, 3.7, and 1.7, 1.2%, respectively. The proposed method has been applied to analyze water sample with satisfactory results. (C) 2000 Elsevier Science B.V. All rights reserved.

Construction of a heteropolyanion-modified electrode by a two-step sol-gel method and its electro catalytic applications

The sol-gel technique was used here to construct heteropolyanion-containing modified electrodes. This involves two steps, i.e. the first forming a functionalized sol-gel thin film on the surface of the glassy carbon electrode and then immersing the electrode into a heteropolyanion solution to incorporate the heteropolyanion into the sol-gel film. Here a Dawson-type heteropolyanion, K6P2W18O62 (P2W18), was used as a representative to illuminate the behavior of the as-prepared composite film. The electrochemical performance of the P2W18-modified electrode was studied with respect to the pH effect and long-term stability. The modified electrode exhibited a high electrocatalytic response for the reduction of BrO3- and NO2-. Steady-state amperometry was applied to characterize the electrode as an amperometric sensor for the determination of NO2-. The sensor had a linear range from 0.02 to 34 mM and a detection limit of 5 x 10(-6) M. (C) 2001 Elsevier Science B.V. All rights reserved.

Determination of allopurinol and its active metabolite oxypurinol by capillary electrophoresis with end-column amperometric detection

A simple method was proposed for the separation of allopurinol (AP) and its active metabolite oxypurinol (OP) by capillary electrophoresis with end-column amperometric detection. A running buffer composed of 15 rum Na2HPO4/NaH2PO4 at a pH 9.55, electrokinetic injection 7 s at 5 kV, separation voltage at 15 kV and detection potential at 1.20 V were investigated to be the optimal condition for the separation. The method exhibited low detection Emit (S/N = 3) as 1 x 10(-8) mol/l for AP and OP, wide linearity range of 2 x 10(-7) to 1 x 10(-4) mol/l, 1 x 10(-7) to 1 x 10(-4) and high efficiency of 1.2 x 10(5) and 1.8 x 10(5) N/m for AP and OP, respectively. The potential application examined for the method was the determination of the spiked urine sample, which was proved to be sensitive and efficient. (C) 2001 Elsevier Science B.V. All rights reserved.

Determination of p-toluene sulfonic acid in phenol matrix by capillary zone electrophoresis with ultraviolet detection

The p-toluene sulfonic acid (MA) in phenol matrix was separated and determined by capillary electrophoresis with ultraviolet detector. the effect of the concentration and pH of the buffer on separation was investigated. Cinnamic acid has been chosen as the internal standard from four compounds, the calibration curves of PTSA in 50 mg/L phenol matrix were obtained with and without the internal standard. The linear range was from 1.25 to 12.5 mg/L and the correlation coefficient was 0.9999 for both curves. The limit of detection of PISA was 0.75 mg/L at 3 times of SIN. Finally, the concentration of PTSA in four synthesized samples was determined with method of standard additions, and the effect of matrix was discussed. The values of MA in these samples were 1.01, 0.94, 1.56 and 0.00 mg/L respectively.

New microsystem of capillary electrophoresis with amperometric detection

We have made a cheap microsystem of capillary electrophoresis with a new method, integrating the electrodes, injection channel, separation channel, buffer reservoirs and detection cell on a polymethylmethacrylate (PMMA) chip. Using an integrated micro carbon fiber disk electrode as the working electrode in three electrodes system, 1 x 10(-4) mol/L dopamine(DA) could be detected with end-column amperometric detection. The reproducibility was good. Peak current was 6.73 nA,theoretical plate number was 71300/m and height equivalent of one theoretical plate height was 14.0 mum for 1 x 10(-4) mol/L DA. The limit of detection was 3.6 x 10(-8) mol/L and the linear range was extended from 5 x 10(-7) mol/L to 1 x 10(-4) mol/L for DA. 1 x 10(-4) mol/L catechol (CA) and 5 x 10(-5) mol/L DA were also separated completely with R-s = 10.1.

End-column amperometric detection of aesculin and aesculetin by capillary electrophoresis

Determination of aesculin (AL) and aesculetin (AT) by capillary electrophoresis with end-column amperometric detection using a 33 mu m microdisk carbon fiber electrode is described. The HDVs, the effect of pH, buffer concentration, injection voltage, injection time and separation voltage on the peak current response (i(p)) of the analytes and the number of theoretical plates (N) were studied. The method has high sensitivity and good reproducibility. Under the optimum condition - 10 mM, pH 9.00 phosphate buffer, 4 s at 9 kV injection, separation at 15 kV and +1.0 V as the detection potential - low detection limits (S/N = 3) of 0.06 and 0.3 mu M were obtained for AL and AT, respectively. The calibration curve was linear over three orders of magnitude. The relative standard deviations (n = 15) of peak current and migration time were 3.9% and 4.6%, and 0.96% and 0.75% for 15 consecutive injections of 5 mu M AL and AT, respectively. The use of this method for the separation and detection of the two compounds present in the traditional Chinese medicine and human urine samples is also reported. (C) 1999 Elsevier Science B.V. All rights reserved.

End-column amperometric detection of 6-mercaptopurine by capillary zone electrophoresis

End-column amperometric detection of 6-mercaptopurine by capillary zone electrophoresis was described with high resolution and speed. The detection conditions were optimized and the electrochemical behavior was observed. Under the optimal conditions: detection potential of 1.2 V ( vs. Ag/AgCl), operating voltage of 15 kV, sample injection of 3 s at 15 kV and 10 mmol/l Na2HPO4 buffer, the detection limit for 6-MP was as low as 1 x 10(-7) mol/L and the linear range was from 5 x 10(-4) to 5 x 10(-6) mol/L with the relative coefficient of 0.995. The RSD of reproducibility for peak current and migration time was 2.5% and 1.2%, respectively. This method was utilized in assay real sample of human mine and bovine serum albumin containing 6-mercaptopurine.

End-column electrochemical detection for aromatic amines with high performance capillary electrophoresis

Electrochemical detection of five species of aromatic amines at a carbon fiber microdisk electrode after separation by capillary electrophoresis is described. Under the optimum conditions, the detection limit for 3,4-dihydroxybenzylamine, N,N-dimethylaniline, p-phenylenediamine, p-aminophenol and aniline sulfate was 0.9, 0.03, 0.075, 1.2 and 0.15 mu M (S/N = 3), respectively. The linear response range was 5-1000, 0.1-500, 0.5-500, 5-500 and 1-200 mu M, respectively The effect of the electrode position and buffer pH on the detection was also studied. This method is very simple, sensitive and stable for the detection of these compounds.