Nucleophilic Addition of Thiaproline to Electrochemically Derived o‐Quinone,Application to the Sensitive Voltammetric Detection of Thiaproline

The mechanism of electrochemical behavior of catechol in the presence of thiaproline is investigated by cyclic voltammetry, controlled‐potential coulometry and spectrophotometric tracing of the reaction coordinate. The results indicate that thiaproline participate in with an ECEC mechanism in a nucleophilic (Michael) addition to o‐quinone. Effect of pH of buffer solution on reaction pathway is studied and showed that addition of thiaproline to the o‐quinone is performed only in solutions with pHs higher than 5. These results indicate that the addition of thiaproline is occurred first from amine functional group. In the second step, the addition of carboxylate group of thiaproline to C‐5 of catechol results the final product with a lactone ring in its structure. Observation of two isosbestic point in absorption spectrum during the progress of the electrolysis together with the FT‐IR results for final product can be presented as evidence for two step addition of thiaproline to catechol. Final product, due to the electron donor property of thiaproline, more easily oxidized respect to the former catechol and as a result, a new redox couple is obtained for this compound in lower potentials. The easier anodic oxidation of addition product (relative to catechol) caused to an increase in anodic current for catechol, which is proportional to the thiaproline concentration. The differential pulse voltammetry (DPV) is applied as a sensitive voltammetric method for the detection of thiaproline. A linear range from 5×10^?8 to 5×10^?6 M with a detection limit of 1×10^?8 M is resulted for thiaproline. With respect to the reversibility of the electrochemical reactions in the mechanism, and also more facile oxidation of the addition products, the square‐wave voltammetry is presented as a method with considerably more sensitivity for the detection of sub‐micromolar amounts of thiaproline. The advantageous properties of the voltammetric method for thiaproline detection lie in its excellent catalytic activity, sensitivity and simplicity.     

大黄素的吸附溶出伏安研究

研究了大黄素在甲醇、二氧六环和水的混合溶剂中以１％硼砂为支持电解质在静汞电极上的吸附伏安行为。建立了用微分脉冲吸附溶出伏安法测定其含量的新方法。在－０３０Ｖ（ｖｓＡｇ／ＡｇＣｌ）电位下吸附富集，可得一灵敏的还原溶出峰，峰电位－０７５Ｖ，浓度在５×１０－８～５×１０－９ｍｏｌ／Ｌ范围内与峰电流具有良好的线性关系，最低检出限为１×１０－９ｍｏｌ／Ｌ。该法用于含有大黄素体系的测定简便、快速、可靠。     

Pulse radiolysis of one-electron oxidation of rare tricyclic nucleoside derivative

~~Pulse radiolysis of one-electron oxidation of rare tricyclic nucleoside derivative@赵红卫$Shanghai Institute of Nuclear Research, Chinese Academy of Sciences! Shanghai 201800,China @江致勤$Department of Chemistry, Tongji Unviersity!Shanghai 200092,China @窦大营$Shanghai Institute of Nuclear Research, Chinese Academy of Sciences! Shanghai 201800,China @吴铁一$Shanghai Institute of Nuclear Research, Chinese Academy of Sciences! Shanghai 201800,China @王文锋$Shanghai…     

Selenium speciation in foods: Preliminary results on potatoes

The present paper deals with the speciation of selenium in potatoes (enriched or not in selenium). The study was carried out by using differential pulse cathodic stripping voltammetry (DPCSV) for quantifying selenium. Results obtained provide evidence that the selenium content in the protein fraction is rather independent from the selenium added to the plants during their growth. On the contrary, the amount of Se in the non-protein fraction (water and starch) in Se-enriched sample is significantly higher than in non-enriched one, suggesting that it is the main selenium-storing site. In this fraction the Se(VI)/Se(IV) ratio seems independent from selenium application but it may be related to the redox conditions. The accumulation of selenium in the non-protein fraction is tentatively ascribed to the “Se–starch interaction” that should be able to modulate both the Se absorption into proteins and, possibly, its toxic effect for the plant itself.     

Voltammetric behaviour and determination of moxifloxacin in pharmaceutical products and human plasma

The oxidative behaviour of moxifloxacin was studied at a glassy carbon electrode in different buffer systems using cyclic, differential pulse, and Osteryoung square-wave voltammetry. The oxidation process was shown to be irreversible over the entire pH range studied (2.0–10.0) and was diffusion-controlled. The methods were performed in Britton–Robinson buffer and the corresponding calibration graphs were constructed and statistical data were evaluated. When the proposed methods were applied at pH 6.0 linearity was achieved from 4.4×10^–7 to 1.0×10^–5 mol L^–1. Applicability to tablets and human plasma analysis was illustrated. Furthermore, a high-performance liquid chromatographic method with diode-array detection was developed. A calibration graph was established from 4.0×10^–6 to 5.0×10^–5 mol L^–1 moxifloxacin. The described methods were successfully employed with high precision and accuracy for estimation of the total drug content of human plasma and for pharmaceutical dosage forms of moxifloxacin.     

二阶导数差示脉冲极谱法用于醋酸氟氢可的松的定量研究

用二阶导数差示脉冲极谱法对醋酸氟氢可的松进行了定量分析。在０．００１ｍｏｌ／Ｌ硫酸＋乙醇＋水（１＋２５＋２４）的底液中，醋酸氟氢可的松于－０．３４０Ｖ（ｖｓＡｇ／ＡｇＣｌ）处出现一良好的二阶导数差示脉冲极谱峰，在５～１４０μｇ／ｍＬ范围内，醋酸氟氢可的松的浓度与其二阶导数差示脉冲极谱峰幅值呈线性关系，检测限为０．４ｎｇ／ｍＬ。本法操作简便、快速、灵敏、结果准确。     

Voltammetry in Undiluted Acetic Acid. In Situ Determination of Water

Water present in undiluted acetic acid can be monitored in situ with Pt and Au microelectrodes using differential pulse and square‐wave voltammetries. Both reduction and oxidation peaks can be obtained. The best quantitative analytical results were obtained for the anodic peak, the Pt microelectrode, and differential pulse voltammetry. The anodic water peak is located at +1.55 V vs. the quasi reference Pt electrode. The voltammetric peak obtained at Pt electrode is apparently not a diffusional one, however, the calibration plot obtained by employing this peak is linear over a wide concentration range, up to 4 mol dm^?3. The detection limit has been estimated as 2.3 mM or 0.0043 v/v%. The developed method may be particularly useful, since the Karl Fischer method can not be used to determine water in glacial acetic acid due to the estrification reaction of acetic acid with methanol. A voltammetric wave of undiluted acetic acid could not be obtained in the positive and negative ranges of potential.     

Electrochemical machining of metals: Fundamentals of electrochemical shaping

Basic problems of metal electrochemical shaping theory are considered. Exact and approxi1mate (quasi-steady-state, locally one-dimensional) methods for solving direct and inverse problems are analyzed. Experimental methods for improving the electrochemical shaping accuracy are considered.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1438–1480.Original Russian Text Copyright © 2004 by Davydov, Volgin, Lyubimov.     

Differential pulse polarographic determination of salicylaldehyde as its Girard-P derivative

A method for the determination of salicylaldehyde (2 × 10^–6–10^–4 M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10^–5 M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid.     

Simultaneous Determination of Aluminum and Iron in High Salt Content Matrices by Adsorptive Stripping Voltammetry. Application to Dialysis Fluids

A new analytical procedure for the simultaneous determination of aluminum(III) and iron(II) in two kinds of dialysis fluids (peritoneal and hemodialysis fluids) by differential pulse adsorptive stripping voltammetry (DPAdSV) is described. The voltammetric measurements were performed using, as working electrode, a stationary mercury electrode, and a platinum electrode and a Ag|AgCl|KCl_(sat.) electrode as auxiliary and reference electrodes, respectively, employing acetate buffer solutions at different pH as supporting electrolyte. As complexing agents, Solochrome Violet RS, Palatine Chrome Black 6BN, Chromazurol S and Eriochrome Black T were employed. For both elements, the accuracy, expressed as relative recovery R%, was very satisfactory being in the range 94–105%, the precision as repeatability, expressed as relative standard deviation s_r%, was lower than 6%, while the limits of detection were of the order of a few units of μg/L. The analytical voltammetric procedure has been validated by comparison with spectroscopic (graphite furnace atomic absorption spectroscopy, GFAAS) measurements.