抗坏血酸的催化动力学光度法测定

建立了一种测定抗坏血酸的方便、快速、高灵敏度的催化动力学光度法。对氨基苯磺酸与亚硝酸根进行重氮化反应生成重氮盐,抗坏血酸对重氮盐的分解有催化作用。利用加入8－羟基喹啉与该重氮盐反应生成偶氮染料来终止反应。在波长495nm处,用1cm比色皿以水作参比测定其吸光度,最佳测定酸度为pH9.0。吸光度与空白体系的差值△A与抗坏血酸的质量浓度呈线性关系。该法测定抗坏血酸的线性范围为0．16－6．3mg/L,检出限为0.005mg/L。利用该法测定了维生素C片剂及荔枝晶中的抗坏血酸含量,并与碘量法进行对照,结果基本吻合。     

Mechanistic aspects associated with the oxidation of -ascorbic acid at the 1,2-dichloroethane water interface

The biologically relevant oxidation of -ascorbic acid (AH₂) was studied at an externally polarised 1,2-dichloroethane water interface by a combination of electrochemical and spectroscopic techniques. In the presence of an electron acceptor (chloranil) in 1,2-dichloroethane, the basic features of the voltammetric signal are dependent on the concentration ratio of the redox species. In the presence of an excess of chloranil, a reversible signal is readily observed. A similar voltammetric response is developed when the semiquinone radical anion of chloranil (Q√⁻) is generated by homogeneous reduction in the presence of decamethylferrocene (DMFc) in the organic phase. These results suggest that Q√⁻ is formed homogeneously rather than by heterogeneous electron transfer from AH₂ to Q under these conditions. However, in the presence of an excess of ascorbate, an irreversible voltammetric response is the dominant feature. Replacing chloroanil by tetracyanoquinodimethane also provides irreversible features indicating that heterogeneous electron transfer can also take place. The occurrence of both homogeneous and heterogeneous electron transfer pathways is also suggested by potential modulated reflectance (PMR) spectroscopy.     

流动注射化学发光抑制法测定痕量抗坏血酸

研究发现在碱性介质下，抗坏血酸对 Luminol-K3Fe（CN）6体系发光反应具有强烈的抑制作用，建立了化学发光抑制快速测定痕量抗坏血酸的新方法。本法测定抗坏血酸的线性范围为4．0×10－8～1．0×10-6mol／L，D．L＝40×10－8mol／L，对1．0×10－7mol／L抗坏血酸连续11次测定的相对标准偏差为0．5％，应用于医用维生素C片剂、维生素针剂以及血样中抗坏血酸的测定，结果满意。     

单分子层γ-氨基丁酸共价修饰玻碳电极同时测定多巴胺、尿酸和抗坏血酸

采用电氧化法制备了一种新型γ-氨基丁酸(ABA)修饰的玻碳电极.X射线光电子能谱(XPS)和循环伏安法研究表明,ABA以单分子层状态以C—N键牢固地共价键合在电极表面.该修饰电极对多巴胺(DA)、尿酸(UA)和抗坏血酸(AA)都具有良好的电化学催化特性.在pH=7.0磷酸缓冲溶液中,DA,UA和AA分别于0.45,0.25和0.07V(vs.Ag/AgCl)有一个良好的、独立的阳极方波伏安峰,表明此修饰电极可用于这3种物质的同时测定.与DA,UA和AA的方波伏安峰电流呈线性关系的浓度范围分别为4.0～400,2.0～500和1.0～600μmol/L,检测限(3δ)分别为1.6,1.2和0.8μmol/L.该修饰电极具有良好的灵敏度、选择性和稳定性,并具有抗污染能力.     

Simultaneous determination of dopamine, ascorbic acid and uric acid at poly (Evans Blue) modified glassy carbon electrode

A sensitive and selective electrochemical method for the determination of dopamine using an Evans Blue polymer film modified on glassy carbon electrode was developed. The Evans blue polymer film modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solution (pH 4.5). The linear range of 1.0 x 10(-6)-3.0 x 10(-5) M and detection limit of 2.5 x 10(-7) M were observed in pH 4.5 phosphate buffer solutions. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid and uric acid. The separation of the oxidation peak potentials for dopamine-ascorbic acid and dopamine-uric acid were about 182 mV and 180 mV, respectively. The differences are large enough to determine AA, DA and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect dopamine in the presence of ascorbic acid and uric acid in physiological samples.     

抗坏血酸还原法制备金纳米花的机理

研究了以抗坏血酸和氯金酸为生长溶液制备金纳米花的反应机理. 结果表明, 通过改变生长溶液中抗坏血酸浓度可以调节小尺寸的初级金粒子在种子表面的聚集方式及金纳米花的熟化速度, 从而影响金纳米花的形貌和光学性质. 协同改变抗坏血酸浓度和pH值, 可实现对金纳米花形貌及光学性质的有效调控. 表面增强拉曼散射(SERS)性能评价结果表明, 抗坏血酸还原法制备的金纳米花表面较清洁, 对罗丹明6G有较好的拉曼增强效果.     

化学发光抑制法测定抗坏血酸

利用抗坏血酸对DTMC H2 O2 化学发光体系的抑制作用 ,研究了对抗坏血酸进行间接测定的可能性。试验发现 ,化学发光猝灭率 (R)与抗坏血酸浓度在 1 0× 10 - 7～ 8 0× 10 - 6 mol·L- 1 范围内呈线性关系 ,检出限达到 8 0× 10 - 8mol·L- 1 (S N =3)。对 1 0× 10 - 6 mol·L- 1 抗坏血酸进行 10次平行测定 ,其化学发光强度猝灭率相对标准偏差为 4 6 %。该猝灭体系不需要额外的掩蔽剂 ,方法简单、选择性好 ,可直接应用于一些食品中微量抗坏血酸的测定。     

Electrocatalytic Determination of Ascorbic Acid Using a Palladium Coated Nanoporous Gold Film Electrode

Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of ascorbic acid (AA) on palladium coated nanoporous gold film (PdNPGF) electrode. The deposition of palladium was done through oxidation of copper UPD layer by palladium ions. This low Pd‐loading electrode behaved as the nanostructured Pd for electrocatalytic reaction. The PdNPGF electrode exhibits excellent electrocatalytic behavior by enhancing the AA oxidation peak current due to synergistic influence of the Pd film and NPGF. The kinetic parameters such as electron transfer coefficient, α, was 0.47 and the voltammetric responses of the PdNPGF electrode were linear against concentration of AA in the ranges of 2.50–33.75 mM and 0.10–0.50 mM with CV and DPV respectively.     

L_(18)的一个案例及其研究

本文对正交设计Ｌ１８（６×３７）的一个案例及其分析方法重新进行了研究，阐述了正交试验设计中一些值得注意的问题     

New microdialysis-electrochemical device for simultaneous determination of ascorbic acid and 5-hydroxyindole-3-acetic acid in rat striatum

A new device combining microdialysis with electrochemical microsensor was developed. It can be applied to monitor the biomolecules in the brain for biological and pharmaceutical research. In this paper, the device was applied to simultaneously determine ascorbic acid (AA) and 5-hydroxyindole-3-acetic acid (5-HIAA) in rat striatum. The microsensor used for the device was poly (sulphosalicylic acid) microsensor, which exhibited a good electrocatalytic effect on oxidization of AA and 5-HIAA. The oxidation currents measured by differential pulse voltammetry (DPV) were linear for AA in the range of 0.02-1.0 mmol l⁻¹, and for 5-HIAA from 0.5 to 10.0 μmol l⁻¹ (r=0.9998 and 0.9991, respectively). The detection limits were calculated to be 0.01 mmol l⁻¹ for AA and 0.25 μmol l⁻¹for 5-HIAA (S/N=3). Studies also showed that co-existing substances in biological fluids did not interfere with AA and 5-HIAA determination when using this microsensor. Since, the substances in the microdialysate are easily oxidized by air, the microdialysate in this device was under the protection of N₂. It was found that the concentrations of AA and 5-HIAA in rat striatum were 215±5 and 6.21±0.61 μmol l⁻¹ (mean±S.E.M., n=7), respectively with this device under the protection of N₂. In addition, the effect of the nitric oxide donor, sodium nitroprusside (SNP), on 5-HIAA in the rat striatum was investigated. It was found that a high concentration of SNP (1.0 mmol l⁻¹) resulted in a 34% increase in 5-HIAA level.