Capillary Electrophoresis With Amperometric Detection Research Articles

Study on electrochemical profiles of Valeriana medicinal plants by capillary electrophoresis

The objective of this work was to develop a high-performance capillary electrophoresis with amperometric detection (CE-AD) method for the determination of pharmacologically active ingredients in extracts of Valeriana medicinal plants. The method was validated for linearity, repeatability, limits of detection (LODs) and limits of quantification (LOQs), etc. The LODs and LOQs of eight compounds were found to be in the range from 1.0 × 10−8 to 1.2 × 10−7 and 3.3 × 10−8 to 4.0 × 10−7 g/mL, respectively. The proposed method was successfully applied for the analyses and comparison of bioactive components in Valeriana samples after a relatively simple extraction procedure, and the resultant “electrochemical profiles” can intuitively demonstrate the content diversity of each electrochemically active ingredient in Valeriana samples from different places and plant parts. It was found the content of bioactive ingredients may vary by an order of magnitude depending on natural conditions, e.g. soil, climate, humidity etc.

On-line focusing of 5-hydroxy-tryptamine type 3 receptor antagonists via the combination of field-enhanced sample injection and dynamic pH junction in capillary electrophoresis with amperometric detection

In the present work, an on-line dual focusing technique based on field-enhance sample injection (FASI) and dynamic pH junction (DypH) was developed for the analysis of two 5-hydroxy-tryptamine type 3 receptor (5-HT3) antagonists ondansetron (Ond) and tropisetron (Tro) by capillary electrophoresis with amperometric detection (CE-AD) system. By preparing the sample in a lower conductivity (FASI condition) and lower pH value (DypH condition) matrix relative to the background electrolyte (BGE) solution, a simple and effective dual focusing approach, FASI–DypH was achieved. In this stacking mode, a large amount of analytes could be electrokinetically injected into the capillary and stacked at the boundary of the sample and the BGE zone as a result of deprotonation and decrease in the electric field. Effects of separation, detection and FASI–DypH focusing conditions were investigated in detail. Under the optimum conditions, good separation for Ond and Tro was achieved within 8min. In comparison with the conventional CE-AD analysis method, the present dual focusing technique enabled the enhancement factors in terms of peak heights to reach 357-fold and 345-fold for Ond and Tro, respectively. The limits of detection (LODs) (S/N=3) for Ond and Tro were 2nM and 5nM, respectively. The intraday and interday repeatabilities (RSDs) were less than 4.5% and 2.9% for peak height and migration time, respectively. The proposed method was successfully applied for the analysis of Ond and Tro in human urine sample.

Simultaneous determination of catecholamines and related metabolites by capillary electrophoresis with amperometric detection

An electrophoretic method was developed for the determination of several important catecholamine markers, namely norepinephrine, epinephrine, dopamine, metanephrine, vanillylmandelic acid and homovanillic acid in urine samples. Under the optimum conditions, the six marker compounds could be well separated with the major coexisting interference compound uric acid within 24 min at a separation voltage of 16 kV in a borate running buffer(80 mmol/L, pH=9.48). Highly linear response can be obtained over three orders of magnitude for the above markers with the low limits of detection ranging from 1.0 ng/mL to 5.0 ng/mL(S/N=3). The proposed capillary electrophoresis with amperometric detection(CE-AD) method has been used to simultaneously determine the six catecholamine markers in urine samples of healthy volunteers and patients suffering from different diseases avoiding redundant measurements and high assay cost; and the electrochemical profiles can suggest more diagnostic information of multiple diseases, which provides a promising and convenient entry into primary diagnoses of several clinical diseases.

Study on the Effect of Moderate Exercise on Lactic Acid Content in Breast Milk by Indirect CE with Amperometric Detection

An indirect high-performance capillary electrophoresis with amperometric detection (CE-AD) method has been developed for determination of lactic acid (LA) in body fluids of lactating postpartum women. Several important factors such as the running buffer additive and concentration, the working electrode potential, the pH value and concentration of the running buffer, the separation voltage and injection time were investigated. Under the optimum conditions, LA could be well separated with co-existing interferences including uric acid (UA) in real samples in a 90-cm-length capillary at separation voltage of 12 kV in 4.0 × 10−6 g mL−1 3,4-dihydroxybenzylamine (DHBA)/40 mmol L−1 H3BO3–Na2B4O7 buffer (pH 7.8). The linearity between peak current and concentration of LA was over three orders of magnitude with detection limit of 5.00 × 10−7 g mL−1 (S/N = 3). This proposed method has been successfully used to study the effects of moderate exercise on LA content in breast milk and urine samples of lactating postpartum women, and assay results showed that LA content in breast milk can return to normal level through 60 min rest without decreasing acceptance by breast-feeding infants, although the LA level did increase by 4–6 times in both breast milk and urine samples at 10 min after moderate exercise.

Analysis of polyphenols inValeriana wallichiiDC by capillary electrophoresis with amperometric detection

Summary High-performance capillary electrophoresis with amperometric detection (CE-AD) has been used for analysis of eight bioactive components of the leaves, stems, and roots of Valeriana wallichii DC, after a relatively simple extraction procedure with ethanol. Under the optimum conditions, the eight components can be well separated or (apigenin and luteolin) separated nearly to baseline within 23 min by use of 50 mM borax (pH 9.2) as running buffer and a separation potential of 16 kV. Linearity was excellent over two orders of magnitude of concentration and detection limits (S/N = 3) ranged from 1.7 × 10−7 to 1.8 × 10−8 g mL−1. This method was used for comparison of the concentrations of the bioactive compounds in different parts of the plant on the basis of their electropherograms or ‘characteristic electrochemical profiles’. Assay results were satisfactory.

A novel capillary electrophoretic method for determining methylglyoxal and glyoxal in urine and water samples

Two non-electroactive biomarkers methylglyoxal (MGo) and glyoxal (Go) in urine and environmental water samples were determined for the first time by capillary electrophoresis with amperometric detection (CE-AD) after derivatizing with an electroactive compound 2-thiobarbituric acid. Experimental conditions of derivatization and CE-AD detection were optimized. Highly linear response was obtained for these two biomarkers over three orders of magnitude with good correlation ( r 2 > 0.999). The limits of detection (LODs) and limits of quantitation (LOQs) of MGo and Go were 0.2 μg L −1 and 1.0 μg L −1, 0.5 μg L −1 and 2.0 μg L −1, respectively. The average recovery and relative standard deviation (RSD) were within the range of 90.9–101.3% and 0.7–2.2%, respectively. The proposed CE-AD method provides a reliable and sensitive quantitative evaluation of MGo and Go in real sample matrices by employing relatively simple and inexpensive instrument.

Study on Rhizoma Chuanxiong based on capillary electrophoresis with amperometric detection

A high-performance capillary electrophoresis with amperometric detection (CE-AD) method has been developed for the analysis of seven bioactive ingredients, namely ferulic acid (FA), vanillin, vanillic acid, p-hydroxybenzoic acid, caffeic acid, gallic acid and protocatechuic acid, in Rhizoma Chuanxiong. The effects of several factors such as the acidity and concentration of running buffer, the separation voltage, the applied potential to working electrode and the injection time were investigated. Under the optimum conditions, the seven analytes could be well separated within 21 min at the separation voltage of 16 kV in a 60 mmol/L borax running buffer (pH 8.7). A 300 μm diameter carbon disk electrode has a good response at potential of +950 mV ( vs. SCE) for all analytes. Good linear relationship was established over three orders of magnitude with detection limits (S/N = 3) ranged from 3.3 × 10 −7 to 6.7 × 10 −9 g/mL. This proposed method has been successfully applied for the determination and comparison of different batches of Rhizoma Chuanxiong samples based on their characteristic electrochemical profiles.

Determination of Effective Ingredients in Compound Sulfamethoxazole Tablets by Capillary Electrophoresis with Amperometric Detection

A high-performance capillary electrophoresis with amperometric detection (CE-AD) method has been used for the determination of three antibacterial sulfa components, sulfamethoxazole (SMZ), sulfadiazine (SD) and trimethoprim (TMP). The effects of several factors on CE-AD were investigated. Under the optimum conditions, the three components could be separated well within 14 min in a 70-cm length capillary at the separation voltage of 18 kV, injection time of 6 s in a 13-mM borax-18 mM potassium dihydrogen phosphate running buffer (pH 5.8). The above three analytes have good linear relationship between peak current and concentration of analytes in the range of 5 × 10 −4−5 × 10 −2 g l −1, 5 × 10 −4−1 × 10 −1 g l −1, and 5 × 10 −4−5 × 10 −2 g l −1, respectively, and the detection limits ( S/N = 3) ranged from 8.0 × 10 −5 to 5.1 × 10 −5 g l −1 for all analytes. This proposed method has been successfully applied for the determination of the main effective components in Compound Sulfamethoxazole Tablets.

Study on extraction efficiency of natural antioxidant in coffee by capillary electrophoresis with amperometric detection

Capillary electrophoresis with amperometric detection (CE-AD) has been used for the determination of catechin, rutin, ferulic acid, o-dihydroxybenzene, chlorogenic acid, caffeic acid, gallic acid, and protocatechuic acid in coffee. Comparison of extraction efficiency of antioxidants using different polar solvents was also conducted by this method. Effects of several important factors including the acidity and concentration of running buffer, separation voltage, and working electrode potential, were evaluated to obtain the optimum analysis conditions. The working electrode was a 300 um carbon disc electrode at an applied potential of +0.95 V (vs. saturated calomel reference electrode). Under the optimum conditions, the analytes can be well separated within 26 min in a 75 cm length fused-silica capillary (i.d. 2.5 × 10−5 m). The current response was linear over three orders of magnitude with detection limits (S/N = 3) ranging from 6.0 × 10−8 to 3.6 × 10−7 g/mL for all analytes.

Determination of Uric Acid in Human Saliva and Urine Using Miniaturized Capillary Electrophoresis with Amperometric Detection

An improved method based on a novel miniaturized capillary electrophoresis with amperometric detection (CE-AD) system was described to study the correlation between the trace amount of uric acid (UA) in human saliva and urine samples for patients suffering from gout disease. Under the optimum conditions, UA can been well separated from its co-existing potential interferences, namely xanthine, hypoxanthine, and ascorbic acid, within 170 s with estimated separation efficiency of 111,210 TP m−1. The proposed miniaturized CE-AD system has been successfully applied for the analysis of UA in less invasive biological samples, which could provide potential application in fast diagnosis of gout.

Electromigration Profiles of Cynomorium songaricum Based on Capillary Electrophoresis with Amperometric Detection

A high-performance capillary electrophoresis with amperometric detection (CE-AD) method has been developed for the simultaneous determination of the pharmacologically active ingredients in Cynomorium songaricum in this work. Under the optimum conditions, phloridzin, epicatechin, catechin, naringenin, rutin, luteolin, quercetin, gallic acid, and protocatechuic acid can be well separated or nearly baseline separated (epicatechin and catechin peaks) within 31 min at the separation voltage of 14 kV in a 50 mmol L(-1) Borax running buffer (pH 9.0). Detection limits (S/N=3) ranged from 5.7 x 10(-8) to 8.5 x 10(-9) g mL(-1) for all nine analytes. This procedure was successfully used for the analysis and comparison of the content difference of C. songaricum samples collected from different places based on their electrophorograms or "electromigration profiles".

Determination of the hydrolysis rate constants and activation energy of aesculin with capillary electrophoresis end-column amperometric detection

Aesculetin is the product of the hydrolysis reaction of aesculin. A high sensitivity and good repeatability method based on capillary electrophoresis with amperometric detection (CE-AD) was developed for simultaneous determination of aesculin and aesculetin in the hydrolysate of aesculin. Under the optimum condition: 10 mmol/L KH 2PO 4–5 mmol/L Na 2B 4O 7 (pH 6.0) buffer, separation at 18 kV and +900 mV (versus Ag/AgCl) as the detection potential, the hydrolysis rate constants of aesculin hydrolysis at 25, 30, 35, 40 and 45 °C in 0.1 mol/L KOH were obtained as 1.45 × 10 −2 min −1, 2.01 × 10 −2 min −1, 2.93 × 10 −2 min −1, 3.76 × 10 −2 min −1 and 5.05 × 10 −2 min −1, respectively. It was calculated that the activation energy for aesculin hydrolysis was 49.4 kJ/mol.

Fast determination of sugars in Coke and Diet Coke by miniaturized capillary electrophoresis with amperometric detection

The fast separation capability of a novel miniaturized capillary electrophoresis with amperometric detection (CE-AD) system was demonstrated by determining sugar contents in Coke and diet Coke with an estimated separation efficiency of 60,000 TP/m. Factors influencing the separation and detection processes were examined and optimized. The end-capillary 300 microm Cu wire amperometric detector offers favorable signal-to-noise characteristics at a relatively low potential (+0.50 V vs. Ag/AgCl) for detecting sugars. Three sugars (sucrose, glucose, and fructose) have been separated within 330 s in a 8.5 cm length capillary at a separation voltage of 1000 V using a 50 mM NaOH running buffer (pH 12.7). Highly linear response is obtained for the above compounds over the range of 5.0 to 2.0 x 10(2) microg/mL with low detection limit, down to 0.8 microg/mL for glucose (S/N = 3). The injection-to-injection repeatability for analytes in peak current (RSD < 3.6%) and for migration times (RSD < 1.4%) was excellent. The new miniaturized CE-AD system should find a wide range of analytical applications involving assays of carbohydrates as an alternative to conventional CE and micro-CE.