Pingang He

Simultaneous determination of flavonoids in chrysanthemum by capillary zone electrophoresis with running buffer modifiers

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.

Voltammetric determination of sequence-specific DNA by electroactive intercalator on graphite electrode

Abstract A synthesized 24-mer single-stranded deoxyribonucleic acid (ssDNA) was covalently immobilized onto a chemically-modified graphite electrode with surface-bound primary amino groups, using water-soluble 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC). The immobilized ssDNA was hybridized with various concentrations of complementary DNA (cDNA) in hybridization buffer solution containing ethidium bromide (EB). The dsDNA/EB system was formed on the electrode surface. The anodic waves of the EB bound to the double-stranded DNA (dsDNA) in cyclic voltammetry were used for the determination of cDNA. The anodic peak currents (ipa) of EB were linearly related to the concentrations of cDNA between 1 × 10−4mg ml−1 and 1 × 10−6mg ml−1. The detection limit was about 2 × 10−7mg ml−1.

Determination of four kinds of carbamate pesticides by capillary zone electrophoresis with amperometric detection at a polyamide-modified carbon paste electrode

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 alpha-naphthol, which could be determined by amperometry after capillary electrophoretic separation. Under the selected optimum conditions, the four analytes could be perfectly separated within 23min. The linear ranges of 2-sec-butylphenol, 2-isopropylphenol and m-cresol were from 1.0x10(-7) to 2.0x10(-5)molL(-1) and that of alpha-naphthol was from 2.0x10(-7) to 2.0x10(-5)molL(-1) and their detection limits were 3.0x10(-8), 3.0x10(-8), 3.0x10(-8) and 6.0x10(-8)molL(-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.

Determination of hydroxyl radical by capillary zone electrophoresis with amperometric detection.

Hydroxyl radical (OH*) can cause severe damage to cells and tissues. However, its analysis is very difficult for its high reactivity and very short half-life. In this paper, a simple and highly sensitive method, capillary zone electrophoresis with amperometric detection (CZE-AD) was introduced indirectly to determine OH* by determining its reaction products with salicylic acid (SAL), 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA). The optimum conditions of CZE-AD for the determination of 2,3-DHBA and 2,5-DHBA were explored. Under the optimum conditions, SAL, 2,3-DHBA and 2,5-DHBA could be perfectly separated within 15 min, and the linearity ranges of 2,3-DHBA and 2,5-DHBA were between 1.0 x 10(-7) and 1.0 x 10(-4) mol l(-1). Their detection limits were as low as 2 x 10(-8) mol l(-1), which were much lower than that in CE-UV method. The method was also applied to study the free OH* scavenging activity of angelica polysaccharide. The experimental results showed that this CZE-AD method was very sensitive and practical in both the determination of free OH* and the evaluation of free OH* scavenging activities of antioxidants.

Simultaneous determination of food-related biogenic amines and precursor amino acids by micellar electrokinetic capillary chromatography with electrochemical detection

Abstract A simple and reproducible method, based on micellar electrokinetic capillary chromatography (MECC) with amperometric detection (AD), for the separation and determination of the biogenic amines and their precursor amino acids was studied in this paper. The optimal conditions of separation and detection of typtamine, tyramine, tryptophan and tyrosine were 0.020 mol l −1 borate–NaOH (pH 10.35) containing 0.03 mol l −1 sodium dodecylsulphate (SDS) as running buffer, 20 kV as separation voltage, and +800 mV (vs. SCE) as detection potential. Under the optimum conditions, the four analytes were separated completely within 15 minutes, and good linearity, reproducibility and recovery results were obtained. Based on three times standard deviation of a low level sample, the detection limits for the four analytes were as low as at 10 −7 mol l −1 level. This method was also successfully used in the analysis of actual rice spirit, and satisfactory assay results were obtained.

Separation and determination of nitroaniline isomers by capillary zone electrophoresis with amperometric detection

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, 17kV as separation voltage and 1.10V (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 x 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.

Determination of four polyphenolic active ingredients from a pharmaceutical preparation by capillary zone electrophoresis with amperometric detection

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 microm 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%.

Four-potential-step differential amperometry in a dual-potential sequence mode

Abstract An amperometric waveform was designed for the resolution of overlapped peaks in voltammetry. The waveform is formed by superimposing a small-amplitude square-wave sequence on a dual-amplitude double-pulse sequence. Similar to the principle of dual-wavelength spectrophotometry, cadmium and indium can be determined in the presence of each other.