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fragmentation characteristics in the mass spectrometer [ 9 ]. To date, several methods have been proposed for the determination of CAs in various biological samples [ 10–13 ]. Among them, chromatography and capillary electrophoresis (CE) are important due to its

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Abstract  

The study of the chemical behavior of uranium in biological medium is still of great interest. By the use of capillary electrophoresis (CE) and time-resolved laser-induced fluorescence (TRLIF), it is possible to characterize the different complexes of uranium. Hence, CE, using the isoelectric focusing mode (CIEF), allows for the separation of the different complexes as a function of their isoelectric points (pI) and TRLIF as a speciation method leads to the identification at very low level of different uranyl complexes by temporal resolution and spectral deconvolution. Results obtained on various inorganic chemical systems (phosphate, bicarbonate) together with biological systems (citrate, transferrin) will be presented and discussed. The complexation between uranium and human transferrin has been pointed out through CIEF.

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The capillary electrophoresis method has been applied to the speciation study of uranium(VI) at room temperature, in 0.02M citrate buffer solutions, at pH values between 2.5 and 5.5 and at citrate/U ratios between 20 and 40. No negatively charged species have been pointed out at pH values lower than 3. For a pH value higher than 5, the electropherograms are ill-defined and the signals cannot be analyzed simply (owing to a high and rough baseline). In the pH range 3–5, up to 4 peaks can be attributed to U(VI) species. Two of them are likely due to the expected monomer [(UO2)(Cit)]and dimer [(UO2)2(Cit)2]2− complex species and these species are shown to be in quasi-equilibrium with two other species possessing slightly lower migration velocities, [(UO2)H(Cit)(OH)] and [(UO2)2H2(Cit)2(OH)2]2−, respectively. Speciation diagrams calculated by an exact analytical approach are proposed in order to explain the experimental results. A complete agreement between theoretical and experimental results needs to take into account kinetic and hydrolysis effects.

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Abstract  

Capillary electrophoresis (CE) is a useful method for rapid separations of metal cations. Under ideal conditions, CE can provide complete separation of the trivalent lanthanides in less than 10 min. Simple organic ligands must be included in the electrolyte matrix to achieve good resolution between the cations. In this paper, we demonstrate how to use complexation constants from the literature to design separation protocols for the trivalent f-elements.

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Abstract  

The capillary electrophoresis method with direct UV detection is proposed for the determination of nitrite and nitrate in high-salt perchlorate solutions issued from uranium carbide dissolution. The isotachophoretic sample stacking was used to compensate for the perchlorate matrix interference. Simple electrolyte composed of 120 mM formiate buffer, pH 3.8 enabled the nitrate and nitrite determination in the presence of up to 1000-fold excess of perchlorate with 2 µM and 4 µM detection limits for nitrate and nitrite, respectively. The proposed method was applied to the determination of nitrate and nitrite in high-salt non-irradiated uranium carbide dissolution samples.

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A simple and rapid capillary zone electrophoretic method is proposed for the analysis of antioxidants and preservatives in food. The important factors affecting separation and detection, for example pH, and concentration of the buffer electrolyte and organic modifier, were investigated in detail. Separation of five antioxidants (propyl gallate, gallic acid isoamyl ester, gallic acid n-octyl ester, nordihydroguaiaretic acid, and trihydroxybutyrophenone) and one preservative (benzoic acid) was achieved in a 50.5 cm (effective length) × 75 μm i.d fused-silica capillary, with 15 mmol L–1 borate buffer, pH 9.18, containing 25% (v/v) acetonitrile as separation buffer. UV detection was at 219 nm and the applied potential was 25 kV. Regression analysis revealed linear relationships between peak area and amount of each additive from 10 to 1000 μg mL–1 (R = 0.9992–1.0000). RSD of retention time and peak area were 0.44–0.74% and 1.25–4.31%, respectively. The method was successfully used for simultaneous analysis of the six compounds in food with the recoveries from 89.3 to 115.8%.

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The conditions for the synthesis of rhenium compounds (pH, reaction time, concentration of reducing agent) have been determined previously by thin-layer chromatography. A Britton-Robinson buffer solution has been selected as a carrier electrolyte due to its possible use in a wide interval of pH, mainly at optimal pH for the formation of the complexes studied. The same electrolyte has been previously applied also in case of the study of rhenium and technetium complexes by polarography. The electrophoretic experiments have been carried out under both standard and reverse polarities with direct UV detection at the wavelength 214 nm and 20 °C. The signal of perrhenate has been observed at the reverse polarity (outlet+, inlet–), of reduced rhenium [probably Re(IV)] under normal polarity. The formation of rhenium complexes with EDTA has been shown by lowering of the cationic rhenium signal due to the addition of the ligand. The rhenium complexes with EDTA are observable at reverse mode of CE. The formation of rhenium complexes with HEDP (hydroxyethylidenediphosphonic acid) has been studied in two different carrier electrolytes — 40 mM Britton-Robinson buffer solution and 50 mM phosphate buffer with 20 mM HEDP. The mechanism of perrhenate reduction by stannous chloride and of the formation of rhenium complexes with EDTA has been determined. The necessity of the presence of ascorbic acid as an antioxidant in the reaction mixture at different pH values has been described as well.

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different wavelengths and the best sensitivity was obtained at 200 nm, Fig. 5 . Fig. 5. Capillary electrophoresis (CE) electropherogram of 10 μg mL −1 standard PSE (MT = 3

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Summary

Capillary electrophoresis with fluorescence detection has been investigated for simple, sensitive, and selective analysis of morphine and 6-acetylmorphine (6-AM) in human urine. The method is based on the reaction of morphine and 6-AM with the freshly prepared diazonium salt of aniline at 0°C. The method is selective in the presence of codeine. Conditions that affect derivatization (diazonium concentration and reaction time) and separation (electrolyte concentration, pH, β-cyclodextrin concentration, organic additives, and separation potential) were studied. When fluorescence detection was used with an excitation wavelength of 350 nm and an emission cutoff filter of 500 nm, good linearity was obtained in the range of 50–2000 ng mL–1 with limits of detection and quantification below 1.0 and 3.3 ng mL–1, respectively. The method was applied to human urine and validated by comparison with previously established capillary electrophoretic methods. Accuracy, repeatability, and intermediate precision of results were comparable. The method is suitable for application in forensic cases for initial screening, and in clinical analysis to prevent overdose-induced toxicity.

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Formaldehyde in aquatic products was determined by micellar electrokinetic capillary chromatography (MEKC) after derivatization with 2,4-dinitrophenylhydrazine. Separation was carried out at 25 °C and 25 kV, using a fused silica capillary (75 µ internal diameter; 50.5 cm effective length) and an ultraviolet detector set at 360 nm. The optimal background electrolyte was 20 mM sodium tetraborate and 20 mM sodium dodecyl sulfate at pH 9.0 with 3 s hydrodynamic injection at 30 mbar. Electrophoretic analysis took approximately 6.5 min. The correlation coefficient of the calibration curve was 0.999 over the concentration range 2.0–100.0 mg L−1, and the LOD and LOQ values were 0.57 and 1.89 µg mL−1, respectively. The recoveries were from 83.7% to 97.2% with steam distillation as the sample pretreatment method.

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