Simultaneous determination of dihydroxybenzene positional isomers by capillary electrochromatography using gold nanoparticles as stationary phase.

The paper describes the enhanced separation of o-, m-, p-dihydroxybenzene by capillary electrochromatography (CEC) using gold nanoparticles (AuNPs) as stationary phase. The effect of the AuNPs concentration upon separation was investigated. The experimental parameters, including separation voltage, pH, and concentration of running buffer, were optimized. Under the optimum conditions, a good resolution of three dihydroxybenzene isomers was obtained within 15 min in a 50 cm effective length capillary modified with 0.02 nmol/L AuNPs at a separation voltage of 16 kV in a 50 mmol/L acetate buffer (pH 5.0). The linear ranges were from 10(-6) to 10(-4) mol/L and the detection limits were as low as 10(-7) mol/L. This method was successfully used to analysis two kinds of hair coloring agent sample with recoveries in the range of 90-105% and relative standard deviations (RSD) less than 5.0%.

Determination of fumaric and maleic acids with stacking analytes by transient moving chemical reaction boundary method in capillary electrophoresis.

The paper presents an on-line transient moving chemical reaction boundary (MCRB) method for simply but efficiently stacking analytes in capillary electrophoresis (CE). The CE technique was developed for a rapid determination of fumaric and maleic acid. Based on the theory of MCRB, Effects of several important factors such as the pH and concentration of running buffer and the conditions of stacking analytes were investigated to acquire the optimum conditions. The optimized separations were carried out in a 20 mmol/L sulphate neutralized with ethylenediamine to pH 6.0 electrolytes using a capillary coated with poly (diallyldimethylammonium chloride) and direct UV detection at 214 nm. The optimized preconcentrations were carried out in 50 mmol/L borax (pH 9.0). The calibration curves were linear in the concentration range of 1.0×10⁻7-1.0×10⁻4 mol/L and 5.0×10⁻7-1.0×10⁻4 mol/L for fumaric and maleic acid with correlation coefficients higher than 0.9991. The detection limits were 5.34×10⁻8 mol/L for fumaric acid and 1.92×10⁻7 mol/L for maleic acid. This method was applied for determination of fumaric acid in apple juice and of fumaric and maleic acid in dl-malic, the recovery tests established for real samples were within the range 95-105%. This work provided a valid and simple approach to detect fumaric and maleic acid.

[Study on solid phase extraction and spectrophotometric determination of uranium in water with 2-(2-quinolylazo)-5-dimthylaminophenol].

A new chromogenic reagent 2-(2-quinolylazo)-5-Dimthylaminophenol (QADMAP) was synthesized, and its structure was verified by elemental analysis, infrared spectrum, 1H nuclear magnetic resonance spectrum, mass spectrumand UV-spectrum. The color reaction of QADMAP with uranium was studied. In the presence of pH 7.8 buffer solution, when fluorin ion and TritonX-100 medium exist, QADMAP can react with uranium and fluorin to form a stable 1 : 1 : 1 stable complex [F- :QADMAP : U(VI)]. The molar absorptivity is 1.05 x 10(5) L x mol(-1) x cm(-1) at 590 nm. Beer's law is obeyed in range of 0-20 microg/10 mL. The uranium in samples can be enriched and separated by solid phase extraction with TBP resin cartridge. This method is applied to the determination of uranium in water sample. The relative standard deviations are 2.2%-3.6%, and the recoveries are 94%-105%.

Comparative study on the chiral separation of phenyl alcohols by capillary electrophoresis and liquid chromatography.

Structurally related phenyl alcohols were separated by capillary electrophoresis and liquid chromatography. A statistical experimental design was used in order to optimize the main electrophoretic parameters such as pH, concentration of selector and separation voltage in capillary electrophoresis (CE). Response surfaces were derived using the mathematical model and used for a selection of the optimal experimental conditions. Concentration of the chiral selector, the distance between the aromatic group and asymmetric center of the analytes, were identified as the factors influencing the complexation, selectivity and resolution. Experiments were also performed by high-performance liquid chromatography (HPLC) and the results of CE and HPLC were compared.

[Electrochemical behavior of dopamine at the poly (isonicotinic acid) modified glassy carbon electrode].

AIM: To study the determination of dopamine (DA) in the presence of ascorbic acid (AA) using poly (isonicotinic acid) film modified electrode. METHODS: The cyclic voltammetry and differential pulse voltammetry were used to study the electrochemical behavior of DA at the poly (isonicotinic acid) film modified electrode. RESULTS: The poly (isonicotinic acid) film modified electrode showed an electrocatalytic effect on DA, and shifted the oxidation of AA to negative potential. The difference between the oxidation potentials of DA and AA was 204 mV, thus, AA did not interfere with the determination of DA. The linear range between the anodic currents and DA concentration was: 1.0 x 10(-7)-2.0 x 10(-5) and 2.0 x 10(-5)-1.0 x 10(-4) mol.L-1. The detection limit was 8.0 x 10(-9) mol.L-1. CONCLUSION: The useful life period of the modified electrode is three weeks at least. The modified electrode can be used to the determination of DA in the sample.

[Determination of six effective components in Rheum by cyclodextrin modified micellar electrokinetic chromatography].

AIM: To determine six effective components (aloe-emodin, rhein, emodin, rhaponticin, physcion and chrysophanol) in Rheum. METHODS: Using buffer solution containing 20 mmol.L-1 borax, 20 mmol.L-1 sodium deoxycholate (SDC), 20 mmol.L-1 sodium taurocholate (STC), 15 mmol.L-1 beta-cyclodextrin (beta-CD) and O-phthalic acid as the internal standard, the six components were determined by cyclodextrin modified micellar electrokinetic chromatography. RESULTS: In less than 25 min, aloe-emodin, rhein, emodin, rhaponticin, physion and chrysophanol were separated. The separation conditions were optimized by adjusting buffer pH, concentrations of SDC, STC and beta-CD. The linearity ranges of aloe-emodin, rhein, emodin, rhaponticin, physcion and chrysophanol were 4-34, 5-40, 4-60, 5-80, 6-90 and 5-85 micrograms.mL-1 respectively. Relative standard deviation (RSD) of the method was less than 2.2%. The recoveries of aloe-emodin, rhein, emodin, rhaponticin, physcion and chrysophanol were 100.0%, 98.3%, 100.4%, 94.6%. 95.2% and 93.8% respectively. Raw Rheum, Mongolian Rheum and Rheum tanguticum samples were analyzed. CONCLUSION: This method can be an effective one for identification of Rhubarb.

[Analysis of carbaryl and other pesticides by capillary electrophoresis].

Five pesticides, i.e. carbaryl, simazine, atrazine, arnetryne and prometryn were separated by capillary electrophoresis technique. The effects of experimental parameters including pH, the concentration of surfactant and organic modifier on the separation were investigated. From the experiments, we found the optimum electrophoretic conditions were as follows: 20 mmol/L borate-50 mmol/L sodium dodecyl sulfate-10% methanol (volume fraction) as the running buffer (pH 9.2), applied voltage of 25 kV, detection wavelength of 225 nm. Under the optimum conditions, baseline-separation of each component has been obtained using anionic surfactant for micellar electrokinetic chromatography. The results indicated that the calibration curve of carbaryl was linear in the range of concentrations 30 mg/L-200 mg/L. This method has been applied to the determination of real sample with satisfactory results obtained, and the recovery of carbaryl was 93.4%-101.3%, and the relative standard deviation of peak area was 2.59%.