聚萘胺化学修饰电极对抗坏血酸的电催化研究(Ⅰ)

有关苯胺、苯酚类修饰电极前人做了大量工作,而对萘胺类物质的研究则相对较少.本文研究了萘胺聚合膜与过渡金属离子络合特性及其在碱性溶液中的电催化行为,发现聚萘胺薄膜经过渡金属离子处理后对某些氨基酸及抗坏血酸等有机酸的电氧化有催化作用,抗坏血酸浓度1×10~(-6)～1×10~(-4)mol/L范围内与催化电流值呈良好的线性关系.     

Electrogenerated Chemiluminescence Determination of Dopamine and Epinephrine in the Presence of Ascorbic Acid at Carbon Nanotube/Nafion‐Ru(bpy)$\rm{ {_{3}^{2+}}}$ Composite Film Modified Glassy Carbon Electrode

Based on the inhibition effect of dopamine and epinephrine on Ru(bpy) ‐tripropylamine electrogenerated chemiluminescence system, the excellent properties of carbon nanotube, and the cation permselectivity of Nafion film, an electrogenerated chemiluminescence inhibition method for determination of dopamine and epinephrine in the presence of ascorbic acid at carbon nanotube/Nafion‐Ru(bpy) composite film modified glassy carbon electrode was described. The results showed that the proposed method was sensitive and selective for the determination of dopamine and epinephine. The linear calibration range was from 1.6×10^?9 M to 3.2×10^?5 M and 5×10^?8 M to 6×10^?5 M for dopamine and epinephrine, respectively. 200‐fold excess of ascorbic acid did not interfere with the determination of 1 μM dopamine and epinephrine.     

The spectrophotometric multicomponent analysis of a ternary mixture of ascorbic acid, acetylsalicylic acid and paracetamol by the double divisor-ratio spectra derivative and ratio spectra-zero crossing methods

The double divisor–ratio spectra derivative and ratio spectra–zero crossing methods were applied to the analysis of an effervescent tablet containing the title compounds without using a chemical separation procedure. In the use of both methods, the calibration graphs were linear in the range of 8–28 μg ml⁻¹ for three compounds. Comparison of the results obtained by the two methods indicates that both methods gives the best results.     

光化学反应在分析化学中的应用研究 光激活产生碘测定食品中的抗坏血酸

本文探讨了酸性介质中于紫外光的照射下,利用光激活产生碘的光化学动力学法测定抗坏血酸的可能性。结果表明,在0.25mol/L的硫酸介质中,在过量碘化钾的存在下,抗坏血酸的含量与到达滴定终点的时间在较宽的浓度范围内呈良好的线性关系。用于蜂蜜,黄瓜、蕃茄及Vc药片等样品分析,其相对标准偏差均在1％以下,准确度令人满意。     

Repetitive determination of ascorbic acid using iron(III)-1.10-phenanthroline-peroxodisulfate system in a circulatory flow injection method

Ascorbic acid (AA) could be determined in large quantities of a co-existing oxidant. The incorporation of an on-line reagent regeneration step based on redox reaction eliminates the baseline drift in the procedure. This makes it possible to adopt a circulatory flow injection method (cyclic FIA) and to determine AA repetitively. The method is based on the reduction of iron(III) to iron(II) by the analyte, the reaction of the produced iron(II) with 1,10-phenanthroline (phen) in a weak acidic medium to form a colored complex, and the subsequent oxidation reaction of iron(II) to iron(III) by the co-existing peroxodisulfate. A solution (50 ml) of 3.0×10⁻⁴ mol l⁻¹ ferric chloride, 9.0×10⁻⁴ mol l⁻¹ phen and 5.0×10⁻² mol l⁻¹ ammonium peroxodisulfate in acetate buffer (0.2 mol l⁻¹, pH 4.5) is continuously circulated at a constant flow rate of 1.0 ml min⁻¹. Into this stream, an aliquot (20 μl) of the sample solution containing AA is quickly injected by means of a six-way valve. The complex formed is monitored spectrophotometrically (at 510 nm) in the flow system. The stream then returns to the reservoir after passing through a time-delay coil (50 m). The iron(II)–(phen)₃ complex is oxidized to iron(III)–(phen)₃ complex by peroxodisulfate which exists excessively in the circulating reagent solution. The proposed method allows as many as 300 repetitive determinations of 15 mg l⁻¹ AA with only 50 ml reservoir solution. The contents of AA in commercial pharmaceutical products were analyzed to demonstrate the capability of the developed system.     

Application of heated electrodes operating in a non-isothermal mode for interference elimination with amperometric biosensors

Heated electrodes were applied for the non-isothermal operation of amperometric glucose biosensors based on glucose oxidase immobilised on the electrode surface by entrapment within a polymer layer. The localised deposition of the polymer film under simultaneous entrapment of the enzyme was achieved by an electrochemically induced pH-modulation in the diffusion zone in front of the electrode, thus altering the solubility of the polymer chains. This non-manual sensor preparation protocol could be successfully used for the modification of a novel indirectly heated electrode. The non-isothermal operating mode allows working at the optimum temperature of the enzyme sensors without any thermal distortion of the bulk solution. Increased surface temperature of the sensor thus accelerates transport as well as kinetic processes, resulting in an enhanced amperometric signal.In the presence of interfering compounds such as ascorbic acid, the proposed technique allows use of the diverging thermal impact on the sensing process, for different electrochemically active compounds, for a deconvolution of the amperometric signal at different electrode temperatures. A calculation method for determination of glucose in the presence of one interfering compound is presented as a basis for a calculative interference elimination.     

Citric Acid Determination by Dual Wavelength Spectrophotometry

In this study, a dual wavelength spectrophotometric method was presented on the basis of Cu²⁺‐NH₃ complex decomposition by the citrate ion and the formation of Cu²⁺‐citrate complex. Sum of the absorbance decreasing at 600 nm (λ_max for Cu²⁺‐NH₃ complex) and the absorbance increasing at 750 nm (λ_max for Cu²⁺‐citrate complex) was used in quantification. This method is very selective, fast and inexpensive but relatively less sensitive. The calibration curve is linear in the range of 0.4–8 mmol/L with a detection limit of 0.13 mmol/L. The relative standard deviation (RSD%) for the six repeated determinations (2 mmol/L) is 1.75%. Interference studies of more than twenty common compounds, which are present in the studied samples, were carried out. Only oxalic and ascorbic acids are serious interferes and which interferences were eliminated by simple procedures. Finally, the proposed method was successfully applied in the determination of citric acid content in ORS powder and some fruit juices.     

碘离子选择电极检测催化动力学分析法测定抗坏血酸

在稀硫酸介质中，痕量去氢抗坏血酸对Ｖ（Ｖ）－ＢｒＯ３＾－－Ｉ＾－反应有强烈的催化作用，体系中Ｉ＾－浓度的变化可供碘离子选择电极跟踪检测。据此，本文建立了测定６×１０＾－７￣２×１０＾－５ｍｏｌ／Ｌ抗坏血酸的催化动力新分析法，用于实际样品分析获得较好结果。     

灿烂甲酚蓝褪色光度法测定抗坏血酸

在pH2的HCl缓冲溶液和增敏剂对氨基苯磺酸存在下，抗坏血酸还原灿烂甲酚蓝并使之褪色，褪色反应的体系具有很好的稳定性。在最佳的反应条件下，建立了测定抗坏血酸的新方法，该方法的检出限为0．28mg/L，对0．40mg/L的抗坏血酸测定的RSD为1．2％(n＝11)，线性范围为0．24-32mg/L，方法可应用于药品、合成样品中抗坏血酸的测定。