除锈剂对莲藕铁膜的去除效果研究

分别以采摘后的莲藕和水泥微池中种植的莲藕为材料,比较不同除锈剂对根状茎铁膜的去除效果,以期为莲藕根状茎铁膜的田间防除提供依据。在莲藕采后除铁膜实验中,抗坏血酸在较短时间内将莲藕根状茎上的铁膜完全去除干净,除锈效果好,其次是草酸和柠檬酸。抗坏血酸和柠檬酸混合除锈可提高除锈效率,0.000 87 mol/L柠檬酸和0.012 5 mol/L抗坏血酸共混合处理3 h、0.000 43 mol/L柠檬酸和0.012 5 mol/L抗坏血酸混合处理3 h,可提高除锈效率,减少除锈剂使用。可见将抗坏血酸和柠檬酸按一定比例混合施用对铁膜的去除效果更好,其成本较单独使用抗坏血酸或柠檬酸低。     

流动注射化学发光抑制法测定抗坏血酸

基于抗坏血酸对Ｌｕｍｉｎｏｌ－ＫＩＯ４－Ｈ２Ｏ２体系化学发光反应的抑制作用,建立了化学发光抑制快速测定抗坏血酸的新方法。该方法线性范围为１．０＊１０＾－７－１．０＊１０＾－５ｍｏｌ／Ｌ,检出限为６．０＊１０＾－８ｍｏｌ／Ｌ,对８．０＊１０＾－７ｍｏｌ／Ｌ抗坏血酸１１次平行测定的相对标准偏差为１．０％。用于维生素Ｃ片剂及注射液中抗坏血酸含量的测定,结果令人满意。     

Kinetic spectrophotometric determination of ascorbic acid by reduction of toluidine blue

A simple kinetic method is described for the determination of ascorbic acid. The procedure is based on the reduction of toluidine blue with ascorbic acid. The rate of reaction is followed by measuring the decrease in absorbance of toluidine blue (lambda(max) = 600 nm) as a result of its decolorization upon reduction by ascorbic acid. Ascorbic acid in the range of 3-35 microg/ml was determined using slope and fixed time methods of analysis, while the variable time method allowed the determination of 5-50 microg/ml of ascorbic acid. The percent relative standard deviation of the method varied from 0.78 to 1.32% depending on the kinetic method used. The high sensitivity of the method also allows determination of low levels of ascorbic acid in some fruits and vegetables such as dew melon, water melon, parsley and coriander.     

Biocompatible water-in-oil emulsion as a model to study ascorbic acid effect on lipid oxidation

A biocompatible water-in-oil (W/O) emulsion has been used as a model to study the effect of ascorbic acid (AA) on the oxidation of the oil (glycerol trioleate, GTO) continuous phase. The model system consisted of 3 wt % water dispersed in GTO containing 0.5 wt % sodium oleate (NaO)/oleic acid (OA) mixture (NaO/OA = 20/80 mol/mol %) as a stabilizer. To study the ascorbic acid effect on GTO light-promoted oxidation, we added aqueous solutions of ascorbic acid to GTO in place of distilled water. Results obtained as peroxide values show that ascorbic acid activity depends on its concentration and it is affected by the characteristics of the W/O interface. In the presence of ascorbyl palmitate (AP) or sorbitan trioleate (Span 85) in the continuous phase, ascorbic acid activity increases in the first few hours of oxidation. The effect of ascorbic acid has been related to emulsion structure by calculating characteristic parameters of the droplet size distributions by means of optical microscopy.     

Switch-on fluorescence sensor for ascorbic acid detection based on MoS2 quantum dots-MnO2 nanosheets system and its application in fruit samples

In this work,molybdenum disulfide quantum dots(MoS_2 QDs) were firstly prepared by hydrothermal method using sodium molybdate and glutathione as precursors,and applied in ascorbic acid detection.When joining MnO_2 nanosheets into MoS_2 QDs solution,they produced an obvious fluorescence quenching,which should be due to inner filter effect(IFE).Meanwhile,the fluorescent probe was formed,Interestingly,we found that this quenching phenomenon disappeared with the addition of ascorbic acid,In other words,the fluorescence gradually restored.This recovery phenomenon is mainly due to the reduction effect of ascorbic acid for MnO_2 nanosheets.Under the optimum conditions,the limit of detection(LOD) of 39 nmol/L for ascorbic acid was achieved with a linear range of 0.33-5.00 μmol/L.The repeatability was better than 5.0% for ascorbic acid in both standard and fruit samples(n = 3).Moreover,the as-fabricated fluorescent sensing system was successfully employed to detect the ascorbic acid levels in hawthorn and jujube with satisfactory results.     

光化学反应在流动注射分析中的应用研究 Ⅳ.亚甲基蓝光化学反应体系测定抗坏血酸

基于抗坏血酸光化学还原亚甲基蓝光化学反应,建立了流动注射光化学反应测定抗坏血酸的新方法。方法线性范围为0.12～5.60μg/ml,进样频率为55～60次/h。应用于医用维生素C片剂中抗坏血酸的测定,结果满意。     

Specific Differential Spectrophotdmetric Determination of Ascorbic Acid in Plants Using Ascorbate Oxidase

Abstract

A specific enzymic-differential spectrophatometric method is described and evaluated for the determination of ascorbic acid in vegetables and medicinal plants. It is based on the absorbance measurement at 593 nm of the complex of ferrous ion with 2,4,6-tris (pyridyl)-S-triazine, which is produced by reduction of ferric ion by ascorbic acid, versus a blank sample treated with ascorbate oxidase. The absorbance difference is linearly related to ascorbic acid from 10 to 100 ug/ml. A standard deviation of ±0.5 ug/ml (n=5) and a mean recovery of 101.47. (98.3–103.3%.) from spiked plant extracts, were found. The method was used to determine ascorbic acid in various plants of the Greek flora. Acacia cvanophvlla was found to be the richest source tested for ascorbic acid (89.6 mq/100 q of leaves). The method is very simple and can be used in routine analysis.     

Kinetic method for determination of ascorbic acid on flow injection system by using its catalytic effect on the complexation reaction of an ultra sensitive colorimetric reagent of porphyrin with Cu(II)

A kinetic method performed on a flow injection system is described for the determination of ascorbic acid by using its catalytic effect on the complexation reaction of Cu(II) with 5,10,15,20-tetrakis(4-N-trimethyl-aminophenyl)porphyrin. The characteristic spectrum of porphyrin (Soret band), which shows intense absorption around 400 nm (epsilon>2.0 x 10(5) cm(-1)M(-1)), was used first time for determining ascorbic acid. By incorporating the complexation reaction into a flow injection system, ascorbic acid could be determined either over a broad dynamic range of 0.1-1000 microg/ml or at a trace level below 5 ng/ml. Good repeatability was also achieved by testing a working standard of 0.1 microg/ml with 10 injections at a throughput of 35 h(-1), obtaining a relative standard deviation of 0.11%. Substances like amino acids, vitamins, sugars, organic acids and metal ions, showed no or little interference even present at high concentrations. The method was validated in the determination of ascorbic acid contents of some commercially available soft drinks by comparison with the official 2,6-dichloroindophenol method with reasonable agreement.     

Comparison between radioimmunoanalysis and Mancini methods for a case of ascorbic acid radioprotection on rats contaminated with tritiated water

The recovery of humoral immune response has been comparatively studied by a radioimmunoanalysis (RIA) method and by Mancini single immunoradial diffusion method in an experiment consisting in chronic contamination with low doses of tritiated water (HTO) and oral administration of high doses of ascorbic acid on rats as radioprotector. The radioprotective effect of ascorbic acid was found to be dependent both on the radiation dose and the amount of ascorbic acid administered.     

Kinetic-spectrophotometric determination of ascorbic acid by inhibition of the hydrochloric acid-bromate reaction

A new analytical method was developed for the determination of ascorbic acid in fruit juice and pharmaceuticals. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolourisation of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The linearity range of the calibration graph depends on bromate concentration. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.6 x 10(-6) M and calibration rang is 8 x 10(-6)-1.2 x 10(-3) M ascorbic acid. The relative standard deviation of seven replication determinations of 8 x 10(-6) and 2 x 10(-5) M ascorbic acid was 2.8 and 1.7%, respectively. The influence of potential interfering substance was studied. The method was successfully applied for the determination of ascorbic acid in pharmaceuticals.     

Determination of glutathione, glutathione disulphide, ascorbic acid and dehydroascorbic acid in tissues by reversed-phase liquid chromatography with electrochemical detection

Summary High-performance liquid chromatography with electrochemical detection was applied to the estimation of glutathione, glutathione disulphide, ascorbic acid and dehydroascorbic acid in various tissues of man, animal, and plant. The simultaneous determination of glutathione and ascorbic acid in tissues was done by a coulometric method. Separation of glutathione and ascorbic acid and unequivocal substance identifications were performed on a 100×4.6 mm RP-18 Spheri 5 column. As mobile phase 0.015 mol/l o-phosphoric acid, pH 2.3 was used. Retention time of ascorbic acid was 5.0 min and of glutathione 10.0 min. Dehydroascorbic acid was determined after reduction to ascorbic acid with dithiothreitol. Glutathione disulphide was reduced at pH 7.5 by -nicotinamide-dinucleotide phosphate and glutathione reductase, EC 1.6.4.2., to regenerate glutathione. To exclude interfering substances, several other compounds present in tissues and foods were investigated. This coulometric method is highly sensitive, specific and simple. Very low concentrations of ascorbic acid, glutathione, dehydroascorbic acid, and glutathione disulphide (<500 pg/injection) could be analysed using this HPLC-ECD method.(on leave to Mexico)     

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。     

Electrocatalytic oxidation and flow-injection determination of ascorbic acid at a graphite electrode modified with a polyaniline film containing electrodeposited palladium

A method for forming a composite film on the surface of a graphite electrode is proposed. Conditions for detecting the maximum catalytic current under batch and flow conditions are determined. A procedure for the electrocatalytic determination of ascorbic acid at the graphite electrode modified with a polyaniline film containing palladium particles is proposed. The catalytic effect of this electrode manifests itself by a ～300-mV decrease in the peak potential of ascorbic acid oxidation and by a multiple increase in the peak current of ascorbic acid oxidation as compared to the unmodified electrode. The linear dependence of the electrocatalytic response of the composite electrode on the concentration of ascorbic acid is observed down to 1 × 10^?8 M and 2.5 nmol of ascorbic acid under batch and flow-injection analysis conditions, respectively.     

非抑制型电导检测离子排斥色谱法分析有机酸

本文以对甲苯磺，酸加硼酸作为淋洗液，采用非抑制型电导检测，研究了离子排斥色谱法分离和检测苹果酸，抗坏血酸，乳酸，琥珀酸，甲酸，乙酸，丙酸等有机酸的色谱条件，并进行了实际样品的分析。     

Determination of ascorbic acid in human plasma with a view to stability using HPLC with UV detection

A method for the measurement of ascorbic acid using HPLC with UV detection and investigation into the protein precipitation techniques with regard to stability and recovery are described. The effectiveness of various protein precipitants was tested. Stability of ascorbic acid samples for analysis was investigated over 10 h. Ascorbic acid samples extracted with metaphosphoric acid were stable on a cooled autosampler (4 degrees C) for at least 10 h (with a decline of 1.8% for ascorbic acid solution and 2.8% for plasma). Perchloric acid as protein precipitant for ascorbic acid was unsuitable (with a decline of 36.0% for ascorbic acid solution and 7.3% for plasma). Analytical performance of this method is satisfactory. The intra- and interassay coefficients of variation were 2.1% (n = 10) and 5.8% (n = 12), respectively. The calibration curve was linear with the tested range of 2.0-250.0 micromol/L. The recovery was 96.1% with CV = 4.8% (n = 6) and the LOD was 3 micromol/L. The preliminary reference ranges of ascorbic acid in a group of blood donors are 50.8 +/- 22.4 micromol/L. This assay is a highly sensitive and reproducible HPLC method for the determination of ascorbic acid in human plasma.     

Selective spectrophotometric determination of ascorbic acid in drugs and foods

A new analytical method was developed for the determination of ascorbic acid. The method is based on the reaction of ascorbic acid with 4-chloro-7-nitrobenzofurazane (NBD-Cl) in the presence of 0.2M sodium hydroxide, where a bluish green colour (lambda(max) 582 nm) is developed after dilution with 50% (v/v) aqueous acetone solution. Beer's law was obeyed in a concentration range of 5-20 microg ascorbic acid/ml with a good correlation coefficient (r = 0.9990). The method was found to be highly specific for the determination of ascorbic acid in the presence of dehydro-ascorbic acid, all other vitamins and minerals possibly present in multivitamin preparations, rutin, salicylamide, acetyl salicylic acid, paracetamol, caffeine, phenylephrine hydrochloride and dipyrone. Moreover, the proposed procedure was also successfully applied for the determination of ascorbic acid in some canned and fresh fruit juices, some vegetables and infant milk products without interference from coloured and other substances present in the plant extracts.     

The use of stabilizers in the UV assay of ascorbic acid

Sodium thiosulphate (0.04%w/v) has been used to stabilize ascorbic acid in aqueous medium. The method has been used to assay ascorbic acid in commercial tablet preparations. It is very accurate, precise and reproducible. It compares favourably with official titrimetric method. The method is simple and can be adopted for the routine assay of ascorbic acid in single component tablet formulations.     

纳米金–壳聚糖修饰电极循环伏安法测定抗坏血酸

介绍纳米金–壳聚糖修饰电极的制备方法及其测定抗坏血酸的分析应用。采用电沉积方法,将氯金酸与壳聚糖的混合电解液直接共沉积,制备了壳聚糖–纳米金修饰玻碳电极的电化学传感器。利用循环伏安法研究了抗坏血酸浓度、p H值等对抗坏血酸在修饰电极上的电化学行为的影响。实验结果表明,修饰电极对抗坏血酸具有良好的电催化氧化作用,抗坏血酸浓度在5×10~(–5)~1×10~(–3) mol/L范围内线性良好,回归方程为I_p=0.433 8c+0.881 9,相关系数为0.998 71。该法可指导纳米金–壳聚糖修饰电极的制备及抗坏血酸含量的测定。     

Indirect determination of ascorbic acid by solid-phase spectrophotometry

Solid-phase spectrophotometry (SPS) technique, in the visible region, was used for the spectrophotometric determination of ascorbic acid based on the reducing effect on iron(III) ion, followed by formation of the iron(II)-ferrozine chelate. The chelate is easily sorbed on a dextran-type anion-exchange gel and the absorbance of the resin at 567 and 800 nm, packed in a 1 mm cell, is measured directly. The apparent molar absorptivity using 100 ml of sample was 2.1×10⁷ l mol⁻¹ cm⁻¹ and it allowed the determination of ascorbic acid in the range 5–90 ng ml⁻¹; the detection limit was 0.91 ng ml⁻¹ and the RSD 0.91% for a concentration of 50 ng ml⁻¹ of ascorbic acid (n=10). The proposed method permits a highly sensitive and selective determination of ascorbic acid without any preconcentration and it has been satisfactorily applied for its determination in fruit juices, pharmaceuticals, urine and conservative liquids.     

Measurement of ascorbic acid and dehydroascorbic acid in gastric juice by HPLC

New methods are presented for measuring total vitamin C and the ascorbic acid/dehydroascorbic acid ratio in gastric juice. Extracts are prepared from a gastric juice which are suitable for direct injection onto a Waters Nova-pak C18 Radial-pak cartridge for high performance liquid chromatography (HPLC) using ultraviolet absorbance at 270 nm for detection. Both enable removal of interfering mucus and mucopolysaccharide breakdown products in a novel way. The first uses mini-columns of Sephadex G-50, run in acidic conditions to remove large molecular weight material while maintaining the ascorbic acid/dehydroascorbic acid ratio as it was in the fresh sample. Addition of dithiothreitol converts the dehydroascorbic acid quantitatively to ascorbic acid, thus enabling measurement of both components. The second method converts all the dehydroascorbic acid to ascorbic acid at the outset. A perchloric acid extract is neutralized and passed through a Sep-Pak C18. A new internal standard, reductic acid, is introduced for ascorbic acid analysis which behaves identically on Sep-Pak C18. Samples are analysed by ion-pair chromatography using 0.02 M NH4H2PO4 buffer (pH 7.1): methanol (80:20 v/v) containing 0.62 g/L tetrapentylammonium bromide. The detection limit was 1 ng ascorbic acid, and chromatography was completed in 5 min. The values obtained by the two independent HPLC methods were in good agreement with each other and with those obtained by the 2,4-dinitrophenylhydrazine colorimetric method.