Spectrophotometric Determination of Vitamin C in Pharmaceutical Preparations using Ammonium Metavanadate

 

Pooja V. Jagasia, Divyadarshani B.

Vivekanad Education Society’s College of Arts, Science and Commerce, Chembur, Mumbai- 4000071

*Corresponding Author E-mail: pooja.jagasia@ves.ac.in

 

ABSTRACT:

A rapid, and accurate direct spectrophotometric method was developed for the determination of vitamin C  in pharmaceutical preparations using ammonium metavanadate as a reagent. This method is based on formation of green colored complex between vitamin C and ammonium metavanadate. The optimum conditions for the determination of vitamin C were established. The maximum absorbance of complex was obtained at 395 nm. Under the optimum conditions, a calibration graph was obtained and a linear relationship between absorbance and analyte concentration was found between 40-320 μg/cm3. The molar absorptivity was found to be 9.0 x 10-4 dm3 mol−1 cm−1. The coloured complex in the extract was found to be stable for 4 hours. The different parameters such as effect of pH,  reagent concentration and accuracy and precision were studied .The proposed method was successfully applied to determination of vitamin C in pharmaceutical preparations such as Amla squash(Nutri value), Orange peel powder, and Astymin drops C.  The effect of foreign ions causing interference that are commonly found with L-ascorbic acid in the samples analyzed were studied by adding different amounts of those species to a solution containing 80.00 μg/cm3 of ascorbic acid. Many of the ingredients commonly found in these formulations did not interfere. The results obtained with the proposed method showed good agreement with those calculated by using known reference method pH metric titration.

 

KEYWORDS: Vitamin C, Ammonium metavanadate, U.V-visible spectrophotometer, Herbal formulation, Pharmaceutical preparations.

 

 

1. INTRODUCTION:

Vitamins helps the human to maintain a healthy diet for the survival. They serve as essential components of the specific coenzymes participating in metabolism and many more specialized activities. Among the vitamins, vitamin C (ascorbic acid) is an essential micronutrient required for normal metabolic function of the body. Vitamin C is defined as the generic term for all compounds exhibiting the biological activity of L-ascorbic acid.

 

Literature survey has revealed that the risk of diseases can be lowered to greater extent by more intake of grains, vegetables and fruits. This might be due to the presence of natural antioxidants which prevent free damage.1 Vitamin C  is essential for the healing of wounds, and for the maintenance of cartilage, bones and teeth. It helps in absorption of inorganic ions, collagen formation, reduces plasma cholesterol level and inhibit nitrosoamine formation.

 

Less consumption of vitamin C in the diet causes the deficiency disease scurvy which can be prevented with as little as 10 mg vitamin C per day an amount easily obtained through consumption of fresh fruit and vegetables.

 

The detailed study of vitamin C including advantages and problems by excess use is reported.2-4Reports have revealed the fact that excess dose of vitamin C increases lymphocyte blast genesis which is associated with prognosis of cancer.5 

 

As an antioxidant, it reportedly reduces the risk of arteriosclerosis, cardiovascular diseases and some forms of cancer6,7. Ascorbic acid is the most important antioxidant in citrus fruit juices and it protects the organism from oxidative stress8.

 

Different spectrophotometric methods have been suggested for the determination of vitamin C. some of them are based on reduction of iron (III) to iron (II) with vitamin C, followed by the complexation of reduced iron(II)with different reagents such as 1,10- phenanthroline9, bipyridine10, and p-carboxyphenyl fluorone11. Few of these methods include  the reduction of Cu(II) to Cu(I) with vitamin C, and the formed Cu(I) interacts with neocuproine12 reagent.  However these methods have few limitations like time consuming due to use of heating step and 20 min for full colour development13, low sensitivity14 and poorer selectivity. Vitamin C have been also estimated by some of the indirect method involving the use of iron(III) – thiocyanate complex and ferrozine. However since the iron(III) – thiocyanate method required expensive, this method is not suitable in simple laboratory work.

 

The main objective of the present study was to optimise a simple and rapid spectrophotometric method for the determination of vitamin C that would be useful in routine industrial lab or pharmaceutical laboratory or quality laboratory.

 

In the present method ammonium metavanadate was found to be a suitable reagent that forms a colored complex with vitamin C in almost neutral solution that forms the basis of spectrophotometric determination. The present method was successfully used for the determination of vitamin C in pharmaceutical samples such as in orange peel powder, Amla squash (Nutrivalue) and Astyminc drops .In order to validate the method the results were tested with  pH metric method.

 

2. MATERIALS AND METHODS:

2.1 Apparatus:

All glassware’s used for experimental purpose were made up of Pyrex or corning glass. The burette, pipette and standard flasks were calibrated by the method described by Vogel.

 

2.2 Instruments:

pH meter: A digital pH meter, was used for pH measurements The pH meter was calibrated by employing the buffer solutions of pH 4.0, 7.0 and 9.2.

Spectrophotometer: The absorption measurements were carried out on a Boush and Lomb spectronic -20, using 1cm matched glass cell. The spectrophotometer is calibrated by measuring the absorption spectra of potassium chromate in KOH solution and that of potassium permanganate in sulphuric acid solution 15.

 

2.3 Preparation of experimental solution:

2.3.1 1000 ppm solution of vitamin C :

A fresh stock solution of vitamin C was prepared by dissolving 0.1g of vitamin C in 100 ml of distilled water. The working solution was prepared by the appropriate dilution of the stock standard solution.

 

2.3.2 0.5% solution of ammonium metavanadate solution :

The reagent was prepared by dissolving 0.5 g of ammonium metavanadate in 100 ml distilled water.

 

Reference method:

Simple acid base titration method using pH meter was used as a reference method to compare the accuracy of results.0.1 N standardised NaOH was used for the pH metric titrations for the pharmaceutical preparations used.

 

Recommended Procedure:

Procedure for spectrophotometric determination of vitamin C using ammonium metavanadate as a reagent:

To 1 cm3 of an aqueous solution containing 1000 ppm of vitamin C, 1 cm3 of 0.5%  ammonium metavanadate was added. The pH of the solution was between 5.0-6.0.The final volume was made to 25 cm3 with distilled water. The amount of vitamin C was determined from a calibration curve prepared by processing solutions containing known amounts of vitamin C through recommended procedure and plotting the graph of absorbance against the concentration of vitamin C.

 

3. RESULTS AND DISCUSSION:

3.1 Absorption spectra:

The proposed method involved formation of greenish color complex between vitamin C and ammonium metavanadate in a medium of pH 5.0-6.0.The absorption spectra of greenish complex against the reagent blank and that of ammonium metavanadate against corresponding buffer blank is shown in fig1.The figure revealed that the complex has maximum absorbance at 395 nm. The reagent has not appreciable absorbance at specified wavelength. The color development was instant and the complex was found to be stable for four hours

 

 

Fig 1. Absorption Spectra( Series1-complex vs blank; series2. Blank Vs Distilled Water)

 

 

3.2 Effect of reagent concentration:

The effect of reagent concentration was studied by varying the reagent concentration from 0.2 % to 0.8%, keeping all the parameters constant.  The absorbance values revealed that quantitative analysis is obtained with concentration of 0.4 % and above.  The excess of reagent solution does not alter the absorbance of complex .0.5% concentration was used for the analysis of vitamin C.

 

Fig2. Effect of reagent concentration(Amount of vitamin C used is 80 ug)

 

3.3 Preparation of calibration curve:

A stock solution of ascorbic acid (1000 ppm) was used for the preparation of working solutions .Working solutions of ascorbic acid were prepared immediately before use in order to prevent loss of analyte due to its instability at low concentrations.1 ml of 0.5% ammonium metavanadate was used as a regent for determination of ascorbic acid content. pH of the resultant solution was observed to be between 5-6.The measurements were carried out at 395 nm.

 

Fig3. Calibration curve

Parameter                          Value

Beer’s range                  :   40-320 μg/cm3 

Molar absorptivity       : 9.0 x 10-4 dm3 mol−1 cm−1 .

Intercept                        :0.014

The Co-orelation            :0.995

 

3.4 Interference study:

To assess the selectivity of the proposed method, interferences caused by those foreign species that are commonly found with L-ascorbic acid in the samples analyzed were studied by adding different amounts of those species to a solution containing 80.00 μg/cm3 of ascorbic acid. The tolerance limit was taken as the amount of foreign ion causing an error of not more than 5% in the recovery of vitamin C. Many of the ingredients commonly found in these formulations did not interfere. The results obtained with the proposed method showed good agreement with those calculated by using known reference method pH metric titration.

 

Interference due to glucose :

As ascorbic acid is largely similar to the glucose by structure, because of their structural similarity, glucose may also form the colored complex with metavanadatre as ascorbic acid. But actually no such interference is occurred as no colored complex was formed between vitamin C and glucose. Other ingredients commonly associated such as Citric acid, Tartaric acid, Sucrose, Fructose did not interfere.

 

The pharmaceutical preparation such as orange peel powder, Amla squash and Astymin c drops which were analyzed contain relatively good amount of vitamin C The method is simple and offers an excellent method for the determination of total vitamin C in pharmaceutical products.

 

3.5 Precision and accuracy:

Precision and accuracy of the method developed were determined by carrying out 8 replicate analysis of solutions each containing 200.0 μg of vitamin C. The average of 8 replicate determinations was taken to calculate standard deviation, variance, and variation from mean at 95% confidence limit.

The average of 8 replicate analyses was 4.94 which vary between 4.94±0.028 at 95% confidence limit. The standard deviation was 0.0394 and the variance was 0.0016.

 

Analysis in pharmaceutical preparations:

1.Orange peel powder: 10 gm of orange peel powder collected from Dombivali area was boiled in 250 ml of distilled water for 5 hrs. The solution was filtered through Whatman paper 41 and diluted to finally 250 ml. 5 ml of the solution was used for the analysis.

 

2.Amla squash (Nutri value): 10 cm3 of squash was diluted to 100 cm3  and 1 cm3  was used for the determination of vitamin C.

 

3.Astymin c drops:  0.1 cm3 of drops was diluted to 100 cm3  and 1 cm3  was used for the determination of vitamin C.

 

Table: Analysis of pharmaceutical products:

Sample

*Proposed method

(µg /cm3)

*Reference method

(µg /cm3)

Claimed value

(µg /cm3)

Orange peel powder

52.00 ± 4.62

49.00 ± 3.35

   -

Amlasquash (Nutri value)

63.33 ±5.76

   -

65

Astymin C drops

66.66 ± 5.77

  -

70

*Average of three determinations

 

CONCLUSION:

The proposed method for spectrophotometric determination of vitamin C is simple, selective, fast as it does not require extraction or heating. The assay methods do not involve any stringent reaction conditions, and non interference from associated substances in the dosage forms and real samples. The methods developed have been utilized to determine vitamin C in different samples.

 

ACKNOWLEDGEMENT:

I thankfully acknowledge the financial support by DBT – STAR college scheme, Department of Biotechnology, Ministry of science and technology. I wish to express my heartfelt thanks to the Management and the Principal Dr.(Mrs.) J.K. Phadnis, V.E.S  College of arts, science and commerce  for providing all  the necessary facilities to conduct the present work.

 

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Received on 08.05.2017         Modified on 28.05.2017

Accepted on 30.05.2017         © AJRC All right reserved

Asian J. Research Chem. 2017; 10(3):341-344.

DOI:   10.5958/0974-4150.2017.00057.8