Charge balance is used in the fourth equation, where the left hand side represents the total charge of the cations and the right hand side represents the total charge of the anions: Redox titration Redox titrations are based on a reduction-oxidation reaction between an oxidizing agent and a reducing agent. A potentiometer or a redox indicator is usually used to determine the endpoint of the titration, as when one of the constituents is the oxidizing agent potassium dichromate. The color change of the solution from orange to green is not definite, therefore an indicator such as sodium diphenylamine is used.
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article has been cited by other articles in PMC. Abstract A method was developed for assessing ascorbic acid concentration in commercial fruit juice by cyclic voltammetry.
The anodic oxidation peak for ascorbic acid occurs at about mV on a Pt disc working electrode versus SCE. The influence of the potential sweep speed on the peak height was studied. The obtained calibration graph shows a linear dependence between peak height and ascorbic acid concentration in the domain 0.
The developed method was applied to ascorbic acid assessment in fruit juice.
The ascorbic acid content determined ranged from 0. Different ascorbic acid concentrations from standard solutions were added to the analysed samples, the degree of recovery being comprised between Ascorbic acid determination results obtained by cyclic voltammetry were compared with those obtained by the volumetric method with dichlorophenol indophenol.
The results obtained by the two methods were in good agreement. Ascorbic acid plays an important role in collagen biosynthesis, iron absorption, and immune response activation and is involved in wound healing and osteogenesis. It also acts as a powerful antioxidant which fights against free-radical induced diseases [ 1 — 5 ].
Nevertheless, an ascorbic acid excess can lead to gastric irritation, and the metabolic product of vitamin C oxalic acid can cause renal problems [ 6 ].
Ascorbic acid is a labile substance, as it is easily degraded by enzymes and atmospheric oxygen. Its oxidation can be accelerated by excessive heat, light, and heavy metal cations [ 1 ].
That is why ascorbic acid content of foodstuffs and beverages represents a relevant indicator of quality which has to be carefully monitored, regarding its variation during manufacturing and storage. Many analytical methods can be used for ascorbic acid determination.
Classic conventional techniques are represented by volumetric methods—titration with an oxidant solution such as dichlorophenol indophenol DCPIP [ 89 ], potassium iodate [ 10 ], or bromate [ 11 ].
Volumetric techniques can suffer from lack of specificity [ 12 ] which limits their use to samples not containing other reducing agents. Other optical methods for vitamin C estimation include spectrophotometrical determination of iodine reacted with ascorbic acid [ 14 ] and chemiluminescence [ 15 ].
Liquid chromatography is a successful method for vitamin C determination when selectivity and specificity are concerned [ 16 — 18 ]. HPLC with electrochemical detection has turned out to be a selective and sensitive method for ascorbic acid assessment in foodstuffs and biological fluids [ 19 — 21 ].
A potentiometric biosensor [ 22 ] for ascorbic acid was made by ascorbate oxidase immobilization in a polymeric matrix, fixed on a graphite-epoxy composite electrode.
Amperometric biosensors were obtained by ascorbate oxidase immobilization on a nylon net [ 23 ] or on a collagen membrane, using a Clark oxygen electrode as transducer [ 24 ]. Vitamin C analysis was also performed by using a glassy carbon working electrode as transducer incorporated in a flow system [ 25 ].
Ascorbic and uric acids were determined by coupling an amperometric technique with flow analysis [ 26 ]. Voltammetric and amperometric measurements were performed in a flow cell, using gold microelectrodes on which Pd was electrochemically deposited.
This sensor was constructed by aniline electropolymerization on a glassy carbon or a screen-printed working electrode.
Kumar and Narayanan [ 27 ] investigated a method for vitamin C assessment based on an amperometric sensor obtained by graphite electrode modification by cobalt ferrocyanide. Vitamin C determination was also performed in an FIA system with biamperometric detection, based on ascorbic acid reaction with iodine [ 30 ].
Voltammetry is an increasingly popular method applied to the determination of ascorbic acid in real samples [ 7 ], because it offers low detection limits, even when compared to more expensive techniques.
It requires little or no sample preparation. This technique provides us with the advantage of a fast analysis as well as with the easiness and rapidity of the standard addition method application.
Because of the low cost of the required equipment as well as simplicity of the employed procedures necessary to determine vitamin C, voltammetry appears to offer an attractive alternative to the titrimetric or instrumental methods mentioned earlier, in particular in food quality control.
It does not require complicated, expensive equipment and well-qualified personnel nor is it laborious or time consuming like the previously mentioned instrumental techniques [ 7 ]. Simultanoeus determination of vitamin C and glucose has also been performed using a voltammetric biosensor integrated in an automated SIA system [ 31 ].
Recently, the use of various voltammetric techniques has been combined with modified ascorbic acid sensors; square-wave voltammetry was used to determine ascorbic acid based on its oxidation at a zeolite modified carbon paste electrode [ 32 ], and the method was applied to ascorbic acid determination in citrus juice.
The results reported in literature regarding the determination of ascorbic acid by cyclic voltammetry are not numerous. Nevertheless, cyclic voltammetry has been previously used for antioxidant content assessment, and in particular low-molecular-weight antioxidants, including ascorbic acid; this technique has turned out to be a convenient methodology, validated for the quantification of low-molecular-weight antioxidant capacity of tissue homogenates, blood plasma, or plant extracts [ 34 ].
Cyclic voltammetry and spectrophotometry showed good agreement for the antioxidant capacity estimation in buckwheat products after hydrothermal treatment [ 35 ].
Kim [ 39 ] evaluated ascorbic acid content after isolation on an anion exclusion column by amperometric detection at a Pt working electrode operating at 0. The vitamin C content in apple juice has been monitored by cyclic voltammetry by means of a Pt working electrode [ 7 ].
The aim of this paper was to investigate a method for ascorbic acid determination by cyclic voltammetry, taking into account that the reported data in literature regarding the determination of ascorbic acid by this method are very scarce.Determination of the concentration of vitamin C by using DCPIP test Description: Practical investigation Determination of the concentration of vitamin C by using DCPIP test Apparatus required: Squeezing pipette/dropper pipette & pipette filler.
The concentration of the DCPIP solution is calculated by using the formula below: CV (Ascorbic acid) = CV (DCPIP) * C refer to concentration * V refer to volume 5 Part D Determination of the Vitamin C Concentration in Fruit Juice 1.
c Pipette 2 cm 3 of vitamin C solution into a test tube. d Using a graduated pipette or a burette, add 1% DCPIP drop by drop to the vitamin C solution. Shake the tube gently after adding each drop.
Testing the concentration of Vitamin C in different juices and fruits. Aim: To test the concentration of Vitamin C in different types of Juice and fresh fruits. Hypothesis: I hypothesize that all the fresh fruits and fresh juices will have more Vitamin C than the processed juices or concentrates.
Download Presentation PowerPoint Slideshow about 'Determination of the concentration of vitamin C by using DCPIP test' - lani An Image/Link below is provided (as is) to download presentation. Calculating the concentration of ascorbic acid (vitamin C) Here is an example of how you can measure the concentration of ascorbic acid (vitamin C) in your original sample of fruit.
Suppose you started with 10 g of tissue and made an extract in 50 cm 3 of water and then in the titration a 1 cm 3 sample of your extract required cm 3 of %.