A simple and selective sensor for the determination of ascorbic Acid in vitamin C tablets based on paptode.

A method for the determination of ascorbic acid in vitamin C tablets based on a very simple paptode design on TLC strips is described. This procedure is based on the reduction of iron(III) with ascorbic acid and the formation of a colorful red complex with immobilized 2,2'-dipyridyl (dipy) on TLC strips. The linear range of the system was 20-200 ppm with a detection limit of 1 ppm and a relative standard deviation of 1.5% (n = 28). The parameters, such as pH, concentration of iron(III), concentration of dipy and the volume of dipy per 1 cm(2) of TLC strips, were optimized. The proposed sensor was successfully applied for the determination of ascorbic acid in vitamin C tablets.     

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.     

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。     

Rapid-flow analysis using differential pulse polarography with automatic sampling

Differential pulse polarography is used in a rapid-flow analysis system for automated determination of lead, zinc and ascorbic acid in acetate-buffered sample solutions, without the need for sample deaeration. By use of a nitrogen-segmented buffer stream at high flow-rates, high-speed sampling at up to 180 samples/hr can be obtained at a flow-rate of 22.8 ml/min through a polarographic flow-cell fitted to the dropping mercury electrode. A linear calibration range of approx. 0.1 x 10(-4)-1.0 x 10(-3)M is found for lead, zinc and ascorbic acid, with respective detection limits of 4.0, 0.8 and 0.2 x 10(-6)M, limited by the high base-line current and high noise-level. Vitamin C tablets can be routinely analysed without prior separation steps, provided the sample and wash solutions are matched in electrolyte composition. A precision of better than 1% RSD is obtained at a sampling rate of 120/hr.     

溴酚蓝修饰玻碳电极测维生素C中抗坏血酸含量

使用溴酚蓝修饰的玻碳电极,以快速循环伏安法测定维生素C片剂中抗坏血酸含量并优化实验条件.结果表明,溴酚蓝(BPB)修饰玻碳电极用于抗坏血酸含量的分析,有良好的稳定性和抗干扰能力.在0.0050~0.1500 g.L-1浓度范围内,峰电流与浓度呈良好的线性关系,R=-0.9991,检出限为0.0010 g.L-1,结果令人满意.     

Routine analysis of ascorbic acid in citrus juice using capillary electrophoresis.

A procedure to monitor citrus juice samples was established to quantitate vitamin C by capillary electrophoresis using a previously developed method. Dilution and filtration were the only preparation requirements and separation was achieved with an uncoated capillary using a 35mM sodium borate buffer (pH 9.3) containing 5% (v/v) acetonitrile at 21 kV and 23 degrees C. Detection was performed by high speed scanning between 200 and 360 nm. From the multiwave length scan, the electropherogram at 270 nm was extracted and used to quantitate ascorbic acid. The ascorbic acid concentration was calculated with an internal standard method, with ferulic acid as internal standard. The level of ascorbic acid during analysis was stabilized with ethylenediaminetetraacetic acid and dithiothreitol was used to reduce dehydroascorbic acid to ascorbic acid to estimate the total vitamin C level. Results were similar to those obtained by liquid chromatography and the method is now used to determine routinely the level of ascorbic acid in citrus juices.     

Determination of pantothenic acid in foods by optical biosensor immunoassay

An optical biosensor inhibition immunoassay was developed using a specific pantothenic acid-binding protein for the quantitation of free pantothenic acid (vitamin B5) in foodstuffs. Samples were prepared by a simple extraction procedure in buffer, and vitamin content was estimated against authentic calibrants in the same buffer. Performance parameters included a working range of 10-5000 ng/mL, a limit of detection of 4.4 ng/mL, precision relative standard deviation of 5.4-7.1% over a range of concentrations, and recoveries > 95% in the matrixes tested. A wide range of foodstuffs, including National Institute of Standards and Technology reference samples, were tested in 3 independent laboratories and the results were compared with microbiological assay and liquid chromatography/mass spectrometry (LC/MS) methods. The results indicate that the biosensor technique is appropriate for the estimation of pantothenic acid in a wide range of foodstuffs.     

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.     

Sequential injection redox or acid-base titration for determination of ascorbic acid or acetic acid

Two sequential injection titration systems with spectrophotometric detection have been developed. The first system for determination of ascorbic acid was based on redox reaction between ascorbic acid and permanganate in an acidic medium and lead to a decrease in color intensity of permanganate, monitored at 525 nm. A linear dependence of peak area obtained with ascorbic acid concentration up to 1200 mg l⁻¹ was achieved. The relative standard deviation for 11 replicate determinations of 400 mg l⁻¹ ascorbic acid was 2.9%. The second system, for acetic acid determination, was based on acid–base titration of acetic acid with sodium hydroxide using phenolphthalein as an indicator. The decrease in color intensity of the indicator was proportional to the acid content. A linear calibration graph in the range of 2–8% w v⁻¹ of acetic acid with a relative standard deviation of 4.8% (5.0% w v⁻¹ acetic acid, n=11) was obtained. Sample throughputs of 60 h⁻¹ were achieved for both systems. The systems were successfully applied for the assays of ascorbic acid in vitamin C tablets and acetic acid content in vinegars, respectively.     

Determination of total vitamin C in fruit juices and related products by liquid chromatography: interlaboratory study

A interlaboratory study was conducted to evaluate a liquid chromatographic (LC) procedure for the determination of total vitamin C in foods at levels of 5-60 mg/100 g. Emphasis was placed on fruit juices, although selected foods were also included in the study. Following dissolution of sample in water, endogenous dehydroascorbic acid was converted to ascorbic acid by precolumn reduction with dithiothreitol at neutral pH. Total ascorbate was determined by C18 reversed-phase LC with a phosphate eluent at pH 2.5, incorporating dithiothreitol to maintain vitamin C in the reduced form, and UV detection at 254 nm. Seven types of fruit juices and foods were tested by 19 collaborators in 7 countries. Three duplicate juices and foods met the criteria for Youden pairs and yielded repeatability relative standard deviation of 5.80-14.66%. Reproducibility relative standard deviation ranged from 6.36 to 35.54% (n = 10) with HORRAT values of 0.82-4.04. The LC method is suitable for routine use in fruit products and foods containing > 5 mg/100 g vitamin C and is recommended for further validation by AOAC INTERNATIONAL and International Fruit Juice Union.     

Spectrophotometric flow-injection determination of ascorbic acid by generation of triiodide

A method is proposed for the flow-injection determination of ascorbic acid (0.1–40 μg ml^?1). Iodine is generated in the flow system as triiodide ion or the triiodide/starch complex giving a steady spectrophotometric signal at 350 or 580 nm, respectively; inverse peaks caused by ascorbic acid samples are measured. The method is applied to the determination of ascorbic acid in a fruit juice, jam and vitamin C preparation.     

Fabrication of multiwalled carbon nanotubes/polyaniline modified Au electrode for ascorbic acid determination

An ascorbate oxidase (AsOx) (E.C.1.10.3.3) purified from Lagenaria siceraria fruit was immobilized covalently onto a carboxylated multiwalled carbon nanotubes and polyaniline (c-MWCNT/PANI) layer electrochemically deposited on the surface of an Au electrode. The diffusion coefficient of ascorbic acid was determined as 3.05 × 10(-4) cm(2) s(-1). The behavior of different electrolytes on electro-deposition was also studied. An ascorbate biosensor was fabricated using a AsOx/c-MWCNT/PANI/Au electrode as a working electrode, Ag/AgCl (3 M/saturated KCl) as standard and Pt wire as an auxiliary electrode connected through a potentiostat. Linear range, response time and detection limit were 2-206 μM, 2 s and 0.9 μM respectively. The biosensor showed optimum response at pH 5.8 and in a broader temperature range (30-45 °C), when polarized at +0.6 V. The biosensor was employed for determination of ascorbic acid level in sera, fruit juices and vitamin C tablets. The sensor was evaluated with 91% recovery of added ascorbic acid in sera and 6.5% and 11.4% within and between batch coefficients of variation respectively for five serum samples. There was a good correlation (r = 0.98) between fruit juice ascorbic acid values by the standard 2,6-dichlorophenolindophenol (DCPIP) method and the present method. The enzyme electrode was used 200 times over a period of two months, when stored at 4 °C. The biosensor has advantages over earlier enzyme sensors in that it has no leakage of enzyme, due to the covalent coupling of enzyme with the support, lower response time, wider working range, higher storage stability and no interference by serum substances.     

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。     

Flow-injection determination of ascorbic acid and cysteine simultaneously with spectrofluorometric detection.

A simple and sensitive spectrofluorometric method was developed for the simultaneous determination of ascorbic acid and cysteine by a flow-injection system. This method is based on the reduction of Tl(III) with ascorbic acid or cysteine in acidic media, producing fluorescence reagent, TlCl3(2-) (lambdaex = 227 nm, lambdaem = 419 nm). The injected sample solution was divided into two separate streams. The first stream was treated with Tl(III) at pH 3.0 and then passed through a 270 cm reaction coil to the flow cell of the spectrofluorometer, where the fluorescence intensity was measured. This signal is related to ascorbic acid and cysteine concentration. The second part of the injected sample solution was treated with Tl(III) in HCl solution and then passed through a 50 cm reaction coil to the flow cell and the fluorescence intensity was measured. This signal is related only to cysteine. Thus, the ascorbic acid content was determined directly by the difference according to the calibration curve. Ascorbic acid and cysteine can be determined in the range of 1 x 10(-6) to 5.0 x 10(-5) M, at a rate of 16 samples per hour. The limits of detection (S/N = 3) were 8 x 10(-7) M for ascorbic acid and 7 x 10(-7) M for cysteine. The influence of potential interfering substances was studied. The proposed method was successfully applied to the simultaneous determination of both analytes in real samples.     

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.     

Carbon paste electrode modified with copper(II) phosphate immobilized in a polyester resin for voltammetric determination of <Emphasis Type="SmallCaps"> l </Emphasis>-ascorbic acid in pharmaceutical formulations

A carbon paste electrode modified with copper(II) phosphate immobilized in a polyester resin (CuP-Poly) is proposed for voltammetric determination of L-ascorbic acid in pharmaceutical formulations. The modified electrode allows the detection of L-ascorbic acid at lower anodic potentials than observed at unmodified electrodes. Several parameters that can influence the voltammetric response of the proposed electrode such as carbon paste composition, pH, scan rate, and possible interference were investigated. The peak current was proportional to the concentration of ascorbic acid in the range 2.0 x 10(-5) to 3.2 x 10(-3) mol L(-1) with a detection limit of 1.0 x 10(-5) mol L(-1). The stability and repeatability of the electrode for the determination of L-ascorbic acid are also discussed. Amperometric response was also recorded for electrocatalytic oxidation of the L-ascorbic acid. Concentrations of the vitamin C in pharmaceutical formulations (tablets) measured using the modified electrode and a titrimetric method are in agreement at the 95% confidence level and within an acceptable range of error.     

Flow injection analysis of trace amounts of NADH with inhibited chemiluminescent detection

The analysis of the ascorbic acid (vitamin C; A.A.) contained in some foodstuff and pharmaceutical samples was performed by a new microcalorimetric method. It uses the oxidation of the vitamin C catalysed by the enzyme ascorbate oxidase (A.O.), which gets the specificity of the reaction. The calibration curve was built under the following operative conditions: 25.00 degrees C, pH 5.6, [A.O.]=11 IU ml(-1), the linearity range is: 3相似文献   

A selective catalytic voltammetric determination of vitamin C in pharmaceutical preparations and complex matrices of fresh fruit juices

A simple, selective and precise voltammetric method for the determination of ascorbic acid in pharmaceutical preparations and fresh fruit juices-complex matrices containing various reducing compounds-is described. The method is based on the electrocatalytic oxidation of ascorbic acid in homogeneous solution using electrogenerated ferriciniumcarboxylic acid as mediator. The pH and mediator concentration affecting the performance of the electrocatalytic oxidation of the analyte were optimized. The method was applied to determine vitamin C in deeply coloured, viscous and turbid fruit juice samples with ascorbic acid contents ranging from 15-45 mg per 100 ml, without further dilution, concentration or other pre-treatment of the samples. The amount of mediator used varied depending on the ascorbic acid concentration in the samples. The method was also used for pharmaceutical analysis using a calibration graph. For fruit juice samples the standard addition technique was adopted to prevent the matrix affecting the accuracy of the determination. The relative standard deviation for the analysis of vitamin C in fruit juices ranged from 1.5-5%. The reliability of the method was established by parallel determination against the official methods.