Determination of Ascorbic Acid Vitamin C

Ascorbic acid is oxidized with the consumption of oxygen in the reaction of ascorbic acid oxidase (EC 1.10.3.3)  

Detected substance Sample volume (pi) Linear up to (mmol/1) Stability CV (%) Correlation with optical methods y = ax + b r References 

The enzyme consists of two identical subunits, each having a molecular weight of 72 000. The Km values are 1.09 mmol/1 for ascorbic acid and 0.59 mmol/1 for oxygen. The pH optimum is at pH 6.0. 

Posadaka and Macholan (1979) and Matsumoto et al. (1981) combined glutaraldehyde-crosslinked ascorbate oxidase with O2 electrodes. The obtained sensors were applied to the determination of vitamin C in food samples. The only compounds interfering were L-iso-ascorbic acid and triosereductone. 

Wasa et al. (1984a) developed a chemically modified enzyme electrode for ascorbic acid. The enzyme was attached to impregnated highly porous carbon together with BSA by glutaraldehyde. In intensively stirred solution the response time of the sensor was only 3 s. The sensitivity dropped to 80% within 3 months. 

---

USE Analytical reagent in the determination of ascorbic acid (vitamin C) which reduces the dye to a colorless hydroxy compd. 

The amount of ascorbic acid (vitamin C CgHgOe) in tablets is determined by reaction with bromine and then titration of the hydrobromic acid with standard base ... 

Enhanced Response to Catechols. An important problem in bio-electroanalytical chemistry is the determination of catechol compounds in the presence of ascorbic acid (vitamin C) ( ). The development of carbon fiber ultramicroelectrodes has allowed for the monitoring of these compounds iji vivo ( ). Because the oxidation potential of ascorbate is very similar to those of catechol compounds, because the concentration of ascorbate is at least an order of magnitude higher than that of the catechol species present in the brain (27), and because ascorbate may become involved in an electrocatalytic reaction sequence with oxidized catechol species leading to loss in voltammetric resolution (29,30), the ability to detect catechols in the presence of ascorbate is a non-trivial problem. 

A 0.930-g sample of ascorbic acid (vitamin C) was dissolved in 95.0 g of water. The concentration of ascorbic acid, as determined by freezing-point depression, was 0.0555 m. What is the molecular weight of ascorbic acid ... 

Practice Problem A The combustionof a 28.1-g sample of ascorbic acid (vitamin C) produces 42.1 g CO2 and 11.5 g H O. Determine the empirical and molecular formulas of ascorbic acid. The molar mass of ascorbic acid is approximately 176 g/mol. 

Earlier, in Sample Problem 7.10, we determined that the empirical formula of ascorbic acid (vitamin C) was C3H4O3. If the molar mass for ascorbic acid is 176.12 g, we can calculate its molecular formula as follows ... 

A 0.552 g sample of ascorbic acid (vitamin C) was dissolved in water to a total volume of 20.0 mL and titrated with 0.1103 M KOH. The equivalence point occurred at 28.42 mL. The pH of the solution at 10.0 mL of added base was 3.72. From this data, determine the molar mass and for vitamin C. 

Two techniques for sorption-spectroscopic determination of ascorbic acid have been proposed. The first one is the recovery by silica modified with tetradecyl ammonium nitrate of blue form of molibdophosphoric HPA in the presence of vitamin C. And the second one is the interaction between the ascorbic acid in solution and immobilized on silica ion associate of molibdophosphoric acid with lucigenine. The detection limits of vitamin C are 0.07 and 2.6 mg respectively. The techniques were successfully applied to the determination of ascorbic acid in fmit juices. 

Ascorbic acid commonly known as vitamin C, is one of the most important water soluble vitamins. Ascorbic acid is involved in many biological processes and it is an essential compound in the human diet [1]. The determination of ascorbic acid has gained increase significance in pharmaceutic, clinical, and food applications. So far, different methods have been developed for determination of ascorbic acid [2, 3]. 

PMMA and Topas microchips with EC detection can be used for determination of vitamins such as L-ascorbic acid (vitamin C) and other compounds such as p-aminophenol and hydrogen peroxide. 

A method of determining airborne iodine has also been reported.241 Here, iodine is absorbed into 5% aqueous KI and spectrophotometrically determined at 590 nm in the form of its complex with starch. This method is selective with respect to bromine and chlorine, and the sensitivity of this method is 0.25 mg of I2 per m3 of air. The concentration of the, 31I isotope in water can be determined by a method involving isotope exchange in the starch-iodine complex.242 Flow-injection determination of ascorbic acid (0.1-40 mg/mL) has been proposed.243 Iodine is generated in the flow system as I3- ions, which are in turn exposed to starch to produce a steady signal at 350 and 580 nm. Ascorbic acid provides inversed maxima which are measured. This method is recommended for analysis of ascorbic acid in fruit juice, jam, and vitamin-C preparations. Use of the blue complex has also been reported for determination of sodium dichloro-isocyanurate in air.244 Obviously the blue reaction is applicable in the determination of amylose, amylopectin, and starch,245-252 as well as modified starches.245,253-255... 

Ascorbic acid (1) is most commonly used for testing the performance of electrodes in redox systems. Thus, a Ag-Ag ascorbate selective electrode was constructed with view to use it for vitamin C determination. Its reproducibility and stability was satisfactory and ascorbate ion concentration could be determined in neutral, alkaline and alcoholic media" . A voltametric study was carried out for the evaluation of graphite-epoxy composite (GEC) electrodes for use in the determination of ascorbic acid and hydroquinone. They were compared with mercury and CPE in similar operating conditions of pH and supporting electrolytes. Like all redox electrodes, also GEC electrodes deteriorate on exposure to air or after repeated usage, and the surface had to be renewed for activation. GEC electrodes were found to be adequate for redox system analyses"". The electrocatalytic oxidation of 1 is an amplification method for determination of specific miRNA strands using the An biosensor described in Table 1 . 

The determination of ascorbic acid in foods is based, in part, on its ability to be oxidized or to act as a reducing agent. The most common method for determination of vitamin C in foods is the visual titration of the reduced form with 2,6-dichloroindophenol (DCIP) (4-7). Variations in this procedure include the use of a potentiometric titration (6), or a photometric adaptation (S) to reduce the diflSculty of visually determining the endpoint in a colored extract. The major criticisms of this technique are that only the reduced vitamin, and not the total vitamin C content of the food, is measured, and that there can be interference from other reducing agents, such as sulfhydryl compounds, reductones, and reduced metals (Fe, Sn, Cu), often present in foods. The DCIP assay can be modified to minimize the effects of the interfering basic substances, but the measurement is still only of the reduced form. Egberg et al. (9) adapted the photometric DCIP assay to an automated procedure for continuous analysis of vitamin C in food extracts. 

The literature contains numerous references to the use of bromine for the estimation of olefinic unsaturation in fats, oils, and petroleum products. A method for the determination of ascorbic acid in vitamin C tablets is given in Section 371-3. 

Ascorbic acid (vitamin C) cures scurvy and may help prevent the common cold. It is composed of 40.92 percent carbon (C), 4.58 percent hydrogen (H), and 54.50 percent oxygen (O) by mass. Determine its empirical formula. 

---