Method For Determination Of Ascorbic Acid Research Articles

Fluorometric turn-on detection of ascorbic acid based on controlled release of polyallylamine-capped gold nanoclusters from MnO2 nanosheets.

A fluorometric turn-on assay is described for ascorbic acid (AA). It is based on the controlled release of polyallylamine-stabilized gold nanoclusters (polyallylamine-AuNCs) from MnO2 nanosheets. In an aqueous solution of near-neutral pH value, the positively charged capped AuNCs are adsorbed on the surface of the negatively charged MnO2 nanosheets. The adsorption leads to the quenching of the fluorescence of the AuNCs. However, in the presence of AA, MnO2 is reduced to Mn2+. This causes the destruction of the MnO2 nanosheets. As a result, the fluorescence of the polyallylamine-AuNCs at 615nm is recovered. This method for determination of AA is inexpensive, sensitive, and selective. It works in the 0.01 to 200μM concentration range and has a 3.2nM detection limit (for S/N = 3). Graphical abstract Gold nanoclusters (AuNCs) and polyallylamine can form polyallylamine-AuNCs to enhance the orangefluorescence of AuNCs. MnO2 nanosheets can absorb polyallylamine-AuNCs, and this results in fluorescence quenching of polyallylamine-AuNCs. Ascorbic acid (AA) can reduce MnO2 nanosheets, in this results in the fluorescence recovery of polyallylamine-AuNCs.

A comparative study: Methods for the determination of ascorbic acid in small and middle sized food analytic laboratories

Although vitamin C is essential as an antioxidant and as a cofactor in a series of enzymatic reactions, the ability for ascorbate biosynthesis was lost in humans. Thus, horticultural products and derived fruit drinks or commercial vitamin C products are considered to be important sources for the ascorbic acid intake in the human diet. These facts underline the importance of analytical methods for ascorbic acid determination in different food products. In our study two spectrophotometric and a fluorometric ascorbic acid determination methods have been compared with each other and with the so-called etalon HPLC method to find the best for small or middle sized food analytic laboratories with a sample number of up to several hundreds. As a result of our experiments we could establish that the OPDA-fluorometric method can be suggested for the determination of samples containing ascorbate at low concentrations. Unfortunately, the analytical properties of the OPDA method with spectrophotometric detection have b...

Direct chronopotentiometric method for ascorbic acid determination in fermented milk products

The conditions of electrochemical oxidation of ascorbic acid using glassy carbon electrode were studied leading to the development of a chronopotentiometric method that was used in the analysis of fermented milk products. The effects of the most important experimental parameters of chronopotentiometry including the type and concentration of the supporting electrolyte, initial potential and oxidation current were investigated and optimised in respect to electro-oxidation of ascorbic acid. The use of 0.15mol/dm3 HCl as a supporting electrolyte yielded a well-defined analytical signal of ascorbic acid at ∼0.97V (versus Ag/AgCl, KCl 3.5mol/dm3). The linear response of transition time on ascorbic acid content was obtained in the concentration range of 0.5–80mg/dm3 with achieved limit of detection of 0.021mg/dm3 and limit of quantification of 0.069mg/dm3. Defined chronopotentiometric method was applied in ascorbic acid quantification in milk products fermented with kombucha culture. The reliability of the proposed chronopotentiometric method was verified by comparison with HPLC and by recovery assays. Statistical comparison showed that there was no significant difference between the results of the proposed and HPLC methods (t=0.4747<t0.05=1.950). In the analysis of real samples, method showed to be simple (no sample pre-treatment), rapid (1–5s), sensitive and reproducible, being suitable for routine analysis of ascorbic acid in fermented milk products. Furthermore, chronopotentiometric method allows analysis of foodstuffs under moderate price, avoiding time-consuming sample preparation steps.

Determination of Ascorbic Acid with Wells-Dawson Type Molybdophosphate in Sequential Injection System

Two-electron reduced heteropolyblue is formed very fast at pH 3.75–4.75 in the reaction between Dawson-type molybdophosphate HPA and ascorbic acid (AsA) (ϵ814 = 1.15 × 104 L · mol−1 cm−1). Simple, fast, and direct SIA method for AsA determination was developed. Under found optimal conditions, linear calibration curve was obtained over the range 3 × 10−6–3.5 × 10−4 mol L−1 AsA, and detection limit (3 s) was 1 × 10−6 mol L−1. The proposed SIA method has high sample throughput of 60 h−1 and small reagent consumption. The procedure was applied to the analysis of pharmaceuticals and juices.

Attenuation of Oxidative Stress After Varicocelectomy in Subfertile Patients With Varicocele

We examined changes due to oxidative damage to spermatozoa and alterations in antioxidant capacity in subfertile patients with varicocele before and after varicocelectomy in a prospective study. A total of 30 young subfertile male patients with varicocele were recruited in this study. Varicocele was diagnosed by physical examination and Doppler ultrasound. Semen analysis was performed in the 30 patients before and 6 months after varicocelectomy using a computer assisted semen analyzer. The parameters for evaluating oxidative stress changes were 4977 bp deletion of mitochondrial DNA in sperm, as detected by polymerase chain reaction, the 8-OHdG (8-hydroxy-2'-deoxyguanosine) content in spermatozoa DNA, as measured by a high performance liquid chromatography electrochemical method, and seminal plasma protein thiols and ascorbic acid, as measured by spectrophotometric methods. Semen quality, including motility, morphology and sperm density, was improved in 22 patients (73.3%) after varicocelectomy. The incidence of 4977 bp deletion of mitochondrial DNA in sperm was 40% (12 of 30 patients) and 13.3% (4 of 30) before and after surgery, respectively. Mean +/- SD 8-OHdG content in sperm DNA, and seminal plasma protein thiols and ascorbic acid were 10.27 +/- 2.24/10(5) 2'-deoxyguanosine, 0.77 +/- 0.75 nmole/ml and 1.87 +/- 0.40 mg/dl before operation, and 5.95 +/- 1.46/10(5) 2'-deoxyguanosine, 3.00 +/- 1.17 nmole/ml and 3.12 +/- 0.94 mg/dl after surgery, respectively. The incidence of 4977 bp deletion of mitochondrial DNA in sperm and the level of 8-OHdG in sperm DNA were decreased, and seminal plasma protein thiols and ascorbic acid were increased significantly in all 30 patients after varicocelectomy. Also, in the 8 patients in whom semen quality did not improve after surgery a significant decrease in 8-OHdG in sperm DNA, and a significant increase in seminal plasma protein thiols and ascorbic acid were observed. Subfertile patients with varicocele had a significant decrease in oxidative damage in sperm DNA and an increase in antioxidant capacity in seminal plasma after varicocelectomy, indicating that surgery is effective treatment in such patients.

Use of an Electrochemically Etched Platinum Microelectrode for Ascorbic Acid Mapping in Oranges

A positionable platinum microelectrode fabricated by electrochemical etching was used to monitor the concentration of ascorbic acid in fruits and vegetables. Studies carried out with ascorbate oxidase confirmed the suitability of the amperometric sensor to measure selectively the ascorbic acid content. The results obtained with the proposed method for ascorbic acid determination in orange juices compared well with those found by iodimetry with coulometrically generated iodine. The standard deviation calculated by measuring limiting current values in voltammograms was found to be 3% (n = 150). The sensor allowed the evaluation of the spatial distribution of ascorbic acid concentration in oranges by in-situ measurements. Ascorbic acid concentration maps show that in a perpendicular cut the concentration is higher near the peel to the center of the fruit. In a parallel cut, the concentration increases with the distance to the stem. A correlation between the ripening stage and the ascorbic acid concentration was also observed from electrochemical measurements, the content being higher in mature fruits.

Comparison of voltammetric and high performance liquid chromatographic methods for ascorbic acid determination in infant formulas

Two methods — voltammetric and high performance liquid Chromatographic (HPLC) — useful for determining ascorbic acid in foods, were compared to ascertain which of them could be used for routine determination of ascorbic acid in infant formulas. Both methods were used to assay 10 identical samples of an adapted cow's milk infant formula and 10 samples of soya protein formula. Precision was determined, the variance of each method was measured, and the methods were compared with each other. The variances of the two methods were not statistically different nor was there any significant difference between the results from the two methods. Therefore, it was concluded that both methods can be used for determination of ascorbic acid in infant formulas. The voltammetric method, because of its simplicity, cheapness and less time-consuming nature, could be used for routine determination.

A simple colorimetric method for ascorbic acid determination in blood plasma

The paper describes a simple method for determination of ascorbic acid using acid phosphotungstate. The reagent has been found to be specific and sensitive to ascorbic acid and can be used for ascorbic acid determination in plasma with good reproducibility.

Iodimetric titrimetric determination of ascorbic acid

The iodimetric method for ascorbic acid determination is recommended for routine testing. Excellent reproducible equivalent points, in colored as well as colorless solutions, may be obtained by the use of a vacuum tube potentiometer (titrimeter). The polarized platinum‐platinum electrode system serves best in this titration. With a polarizing current of 1.5 microamperes (at 1 volt) the equivalent point is sufficiently sensitive at a meter setting of −0.25 volts to enable the use of 0.01 N iodine solutions.