Indirect Determination of Ascorbic Acid with Ammonium Sulfate and Isopropyl Alcohol by Extraction-flotation of Copper

A new method of indirect determination of ascorbic acid(Vc) with ammonium sulfateand isopropyl alcohol by extraction-flotation of copper is studied in this paper. It shows that asmall amount of Cu( II ) can be reduced to Cu( I ) by Vc, then Cu( I ) reacted with the SCN-,which precipitated on the interface of isopropyl alcohol and H2O. A good linear relationshin is observed between the flotation yield(E) of Cu( II ) and the amount of Vc. The detection limi(forVc is 1.76 μg/mL. The method is simple, rapid (5 rain), but suffers from little interference of common anions and cations. It has been successfully applied for the determination of Vc in fruits.     

Indirect Determination of Sulfide by Extraction Flotation Spectrophotometry of Copper(II) with Ammonium Sulfate‐Ethanol‐Water System

A new extraction flotation spectrum method for indirect determination of trace amounts of sulfide by ammonium sulfate‐ethanol‐water system was developed. It showed that Cu(II) could combine with S^2? into precipitate (CuS) which was floated in the surface of ethanol and water in the presence of ammonium sulfate. The sulfide can be indirectly determined by determining the flotation yield of Cu(II). The linear range from 2.4 × 10^?8to 3.2 × 10^?6g/mL and the detect limit of 2.0 × 10^?8g/mL was achieved. The results showed the determination of S^2? was not affected by Pb(II), Zn(II), Cd(II), Fe(II), Co(II),Ni(II), Mn(II) and Cl^?, Br^?, I^?, etc. In the paper, the method was successfully applied to the determination of a trace amount of sulfide in polluted water samples with the advantages of simplicity of equipment, rapidity, low cost, etc.     

The Study of Indirect Determination of Tiopronin by Extraction Flotation Copper(II) with an Ammonium Sulfate‐Water‐n‐Propyl Alcohol System

A novel method for indirect determination of tiopronin by extraction flotation of copper(II) with an ammonium sulfate‐water‐n‐propyl alcohol system was developed. The effects of different parameters, such as acidity, the amount of NH₄SCN and various salts on the flotation yield of Cu(II), have been studied to optimize the experimental conditions. Under the optimum conditions, Cu(II) is reduced to Cu(I) by tiopronin, and the resulting Cu(I) can react with SCN^? to form a white emulsion precipitate CuSCN. In the presence of (NH₄)₂SO₄, the mixture consisting of n‐propyl alcohol and water can be separated into an n‐propyl alcohol phase and a water phase. In the process of phase separation of n‐propyl alcohol from water, the precipitated CuSCN is extracted and stays in the interface of n‐propyl alcohol and water. The amount of tiopronin can be determined by measuring the flotation yield of Cu(II). The detection limit is 0.32 mg L^?1 and the linear range is maintained in the range of 0.40±13.0 mg L^?1 with a correlation coefficient of 0.9991. This proposed method has been successfully applied to the determination of tiopronin in tablets, urine and human plasma with satisfactory results.     

磷钼钨三元杂多酸光度法测定药物中的抗坏血酸

研究了抗坏血酸与磷钼钨三元杂多酸的显色反应,提出了借磷钼钨杂多蓝测定抗坏血酸的分光光度法.最大吸收波长为730nm,抗坏血酸在0.08～10mg/L范围内线性良好.回归方程为A=1.05×10⁴C+0.017,线性相关系数γ=0.9995,表观摩尔吸光系数ξ₇₃₀=1.05×10⁴L·mol^-1·cm^-1,方法检出限为0.04mg/L,回收率为94～102%,相对标准偏差≤1.5%(n=8).本方法由于钨钼的混合配位增强了氧化能力,较之二元杂多酸的方法,省去了水浴加热等操作,只需在室温下反应30min,吸光值至少可稳定6h.过量的黄色杂多酸可加入适量的氢氧化钠溶液分解,从而获得色泽纯正的高灵敏度显色体系.     

磷钼钨三元杂多酸光度法测定药物中的抗坏血酸

研究了抗坏血酸与磷钼钨三元杂多酸的显色反应，提出了借磷钼钨杂多蓝测定抗坏血酸的分光光度法。最大吸收波长为７３０ｎｍ，抗坏血酸在０．０８～１０ｍｇ／Ｌ范围内线性良好。回归方程为Ａ＝１．０５×１０４Ｃ＋０．０１７，线性相关系数γ＝０．９９９５，表观摩尔吸光系数ξ７３０＝１．０５×１０４Ｌ·ｍｏｌ－１·ｃｍ－１，方法检出限为０．０４ｍｇ／Ｌ，回收率为９４～１０２％，相对标准偏差≤１．５％（ｎ＝８）。本方法由于钨钼的混合配位增强了氧化能力，较之二元杂多酸的方法，省去了水浴加热等操作，只需在室温下反应３０ｍｉｎ，吸光值至少可稳定６ｈ。过量的黄色杂多酸可加入适量的氢氧化钠溶液分解，从而获得色泽纯正的高灵敏度显色体系。     

测定抗坏血酸的亚甲蓝褪色光度法

确定了亚甲蓝与抗坏血酸褪色反应的最佳条件,在 pH=2的缓冲溶液和对氨基苯磺酸存在的条件下,抗坏血酸能够很快还原亚甲蓝并使之褪色,褪色反应的体系具有很好的稳定性。该反应的摩尔吸光系数为 2.0× 103 L· mol－ 1· cm－ 1,线性范围 0.4～ 40.0 mg/L。该法具有优良的选择性,常见的能够与抗坏血酸共存的阴、阳离子和还原剂、表面活性剂不干扰测定,应用于药品、饮料、蔬菜中抗坏血酸的测定,获得满意结果。     

Flow Injection Analysis Determination of Ascorbic Acid with Spectrofluorimetric Detection

Abstract

A flow injection system for the fluorescence determination of low level of ascorbic acid is proposed. The method is based on the rapid oxidation of ascorbic acid by thallium(I). The fluorescence signal at 419 nm is proportional to the amount of ascorbic acid in the range of (1.4–28.0) × 10^?7 mole. The relative standard deviations for ten replicate measurements of 1.4 × 10^?6 mole of ascorbic acid was 1.3%. The sample rate of 45 ± 5 sample per hour was achieved. The usefulness of the method was tested in the determination of ascorbic acid in fruit juices and vitamin C tablets.     

溶剂浮选-间接光度法测定抗坏血酸

于pH 7.0的磷酸盐缓冲介质中,CTMAB＋及I3-离子间借静电引力形成离子缔合物,可将其浮选入5.0 mL苯中,此缔合物在溶剂中,于365 nm处有吸收峰,较简单的I3^-离子在相同条件下的吸收峰（350 nm）红移了15 nm。在此溶液体系中存在抗坏血酸时使离子缔合物产生褪色反应,且在抗坏血酸浓度在25μg/50 mL以内时与吸光度的降低值（ΔA）间呈线性关系。在抗坏血酸浓度为6.0μg/50 mL时连续测定6次,所得结果的RSD为1.2%,回收率在96%-101%之间。     

A Spectrophotometric Determination of Ascorbic Acid

A new, simple and sensitive method for the spectrophotometric indirect determination of ascorbic acid in fruits, beverages, and pharmaceuticals is described. In this method, the ascorbic acid reduces Cu²⁺ to Cu⁺ and reacts with 2,9‐dimethyl‐1,10‐phenanothroline (neucoproine) to form Cu (neucoproine)⁺ complex, and it was extracted with N‐phenylbenzimidoylthiourea (PBITU) in chloroform. The apparent value of molar absorptivity of the complex in terms of ascorbic acid is (3.52) × 10⁴ L mole^?1 cm^?1 at λ_max, 460. The detection limit of ascorbic acid is 40 μg L^?1 and the method obeys Beer's law over the concentration range of 0.1–4.0 μg mL^?1. The proposed method was successfully applied for the determination of ascorbic acid in various samples. The validity of the present method was checked by the flow injection analysis (FIA) method.     

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。     

抗坏血酸和尿酸在胶束体系中的电化学行为及选择性测定的应用

以玻碳电极为工作电极,在PBS中用循环伏安法研究了抗坏血酸(AA)和尿酸(UA)在胶束体系中的电化学行为。在溴化十六烷基吡啶(CPB)胶束体系中,AA和UA的氧化峰电流增加,峰电位负移;在十二烷基苯磺酸钠(SDBS)胶束体系中,AA和UA的氧化峰电流减小,峰电位正移。在CPB中,AA和UA的氧化峰电位相差约270 mV,以此建立了AA和UA的同时测定方法。用微分脉冲伏安法测定AA和UA的氧化峰电流分别在1.0×10-6~1.0×10-2mol/L和5.0×10-7~1.0×10-3mol/L的范围内与各自的浓度范围呈良好的线性关系。在200倍AA共存时UA的检出限为5.0×10-6mol/L。此方法可应用于人体尿样中UA的测定,结果令人满意。     

Spectrophotometric Determination of Trace Amounts of Ascorbic Acid

Abstract

Colourless silver-gelatin complex is quantitatively reduced by ascorbic acid to yellow silver sol in water within the pH range 7.5–10.0 at room temperature. The determination of 1–10μg/ml of ascorbic acid is possible at 415 nm in the presence of glycine, alanine, fructose, sucrose, citric, tartaric, oxalic, malic, succinic acids and also in the presence of various reducing agents. The molar absorptivity of ascorbic acid at the δ_max is found to be 21500 lit mol^?1 cm^?1 and the Sandell sensitivity of the sol is 8.18x10^?3 μg ascorbic acid cm^?2 for 0.001 absorbance. The relative standard deviation is ±0.22% and the confidence limit (20 determinations, 95%) being 8.806±0.0093%.     

Determination of Ascorbic Acid by a Composite-Modified Platinum Electrode

Thin composite layers of poly(3,4-ethylenedioxythiophene) and poly(4-lithium styrene sulfonic acid) were formed on a platinum surface. The modified electrode platinum/polyethylenedioxythiophene:poly(4-lithium styrene sulfonic acid) was characterized by cyclic voltammetry, chronocoulometry, and electrochemical impedance spectroscopy. The results showed that the electrode may be used as a working electrode for electroanalytical methods. This electrode was used for the determination of ascorbic acid. The effect of composite layer thickness on the functionality of the electrode was characterized for ascorbic acid determination. Another investigated aspect was the process of ascorbic acid oxidation in solutions of various pH values. The results showed that the modified electrode was suitable for the determination of ascorbic acid in various electrolytes from pH 2 to 7.6 in the presence and absence of buffer solutions. The linear dynamic range of ascorbic acid concentrations corresponded to its concentrations in physiological fluids.     

A New Fluorimetric Method for the Determination of Ascorbic Acid

Abstract

The fluorescent reaction between ascorbic acid(AA) and 2-cyanoacetamide was studied. The experimental results showed that AA can react with 2-cyanoacetamide at pH 12.9–13.3, and form a fluorescent product, which emitted strong fluorescence. The fluorescence intensity was measured at excitation and emission wavelengths of 329 and 380nm, respectively. A linear relationship was obtained between the fluorescence intensity and AA concentration in the range of 0.1–50μg/ml, the regression coefficient is 0.9994, and the detection limit of AA is 0.03μg/ml. (signal-to-noise=3).     

掺铁氰根聚吡咯修饰电极测定抗坏血酸的研究

本文对掺铁氰根聚吡咯电极的聚合、伏安行为、电催化效应及其在抗坏血酸测定中的应用进行了研究。该膜电极性能稳定，对抗坏血酸催化效果好，抗坏血酸浓度在５×１０－６～６×１０－３ｍｏｌ／Ｌ范围内有很好的线性关系，用于测定果汁饮料中抗坏血酸获得满意结果。     

Simultaneous Determination of Uric Acid and Ascorbic Acid Using Edge Plane Pyrolytic Graphite Electrodes

Edge plane pyrolytic graphite electrodes have been applied for the determination of uric acid and ascorbic acid. The separate determination of uric acid was found to produce three linear ranges from 100 nM to 3400 μM with a detection limit of 30 nM found to be possible. Uric acid detection was also explored in the presence of 200 μM ascorbic acid where a detection limit of 52 nM was found to be possible. The detection of ascorbic acid in the presence of uric acid was also explored over three linear ranges of ascorbic acid with a limit of detection of 80 nM. Last the simultaneous determination of both uric acid and ascorbic acid is investigated over the range 100 nM to 1000 μM where detection limits of 50 nM and 120 nM were obtained respectively. Analysis of uric acid in a growth tissue medium was found to be successful, confirming the applicability of the methodology to real matrices. This protocol is shown to provide low detection limits, easy handling (no electrode modification), good voltammetric peak separation of uric acid and ascorbic acid and a wide linear dynamic range.     

The Influence of Gold Nanoparticles on Simultaneous Determination of Uric Acid and Ascorbic Acid

A three-dimensional L-cysteine (L-cys) monolayer assembled on gold nanoparticles (GNP) providing simultaneous detection of uric acid (UA) and ascorbic acid (AA) was studied in this work. The cyclic voltammetry demonstrated that, at a bare glassy carbon electrode (GCE) or planar gold electrode, the mixture of UA and AA showed one overlapped oxidation peak; whereas when the electrode was modified with GNP, the oxidation peaks for UA and AA were separated. While a GNP modified electrode was further modified with L-cys monolayer (L-cys/GNP/GCE), namely, three-dimensional L-cys monolayer, a better separation for UA and AA response was obtained. Interestingly, the L-cys monolayer-modified planar gold electrode presented a block effect on the oxidation of AA, which was facilitated by the three-dimensional L-cys monolayer attributed to its distinct structure. The pH of solution presented a noticeable effect on the separation of UA and AA at GNP modified electrodes with or without L-cys monolayer. Wide concentration ranges from 2 × 10^?6?1 × 10^?3 M to UA and 2 × 10^?6?8 × 10^?4 M to AA could be obtained at L-cys/GNP/GCE.     

抗坏血酸和尿酸在甘氨酸-壳聚糖修饰玻碳电极上的电化学行为及测定

制备了甘氨酸-壳聚糖复合膜修饰玻碳电极(Gly-CTS/GCE),研究了抗坏血酸(AA)和尿酸(UA)在该修饰电极上的电化学行为。结果表明在pH=5.59的磷酸盐缓冲溶液中,AA、UA在Gly-CTS/GCE上均产生灵敏的不可逆氧化峰,其峰电流与浓度在一定范围内呈良好的线性关系。对AA和UA混合溶液平行测定7次,相对标准偏差分别为4.6%、2.9%,表明该电极重现性和稳定性良好。AA、UA在Gly-CTS/GCE电极上的氧化峰峰电位相差340mV,据此可实现对二者的同时检测,并可应用于实际样品测定。     

Electrochemical Behaviors of Ascorbic Acid and Uric Acid in Ionic Liquid

Cyclic voltammetric measurements at platinum electrode have been carried out to investigate the electrochemical oxidation of ascorbic acid and uric acid in ionic liquid, [bmim][BF₄]. It is important that a typical redox couple of ascorbic acid was obtained and it is oxidized to dehydroascorbic acid in [bmim][BF₄]. However, there is no electron-transfer for uric acid and no electrochemical oxidation carried out in the same ionic liquid. It provides a new way to eliminate the interfering between ascorbic acid and uric acid in the study of the electrochemical behaviors for them.