Method of Analysis for Ascorbic Acid : Pharmaceutical Guidelines

Method of Analysis for Ascorbic Acid

Learn how to analyze the Ascorbic Acid in pharmaceuticals including Assay.
1. Description
A white or pale yellow powder or crystal.
2. Identification
A Color Reaction:
To a 5ml of 0.05M iodine solution add 15mg of sample. Color of iodine is discharged.
B. Identification by IR
The infrared spectrum of the sample mixture is concordant with the reference spectrum/ spectrum obtained from ascorbic acid WRS.
Sample preparation: Weigh (2 to 3 mg.) of the sample and weigh (150-200 mg.) of fine dry powder of KBr. Grind the mixture well and transfer the mixture into the sample holder cup and take IR.
Standard preparation: Weigh (2 to 3 mg.) of the ascorbic acid WRS and weigh mg (150-200 mg.) of KBr. Crush in mortars up to fine power and make pellet and record the spectrum or recall the reference spectrum of Ascorbic acid WRS and match.
3. Solubility
Freely soluble in water, practically insoluble in alcohol.
4. Loss on Drying
Limit: Not more than 1.0% w/w.
Weigh 1.000 g of substance in a clean and dried preweighed LOD Bottle. Cover the stopper and gently shake to distribute material to not more than 10 MM height. Place the LOD Bottle in oven and remove cover and leave it also inside the oven. Dry the sample at 60° C for 3 hr under vacuum at 1kg. Release vacuum before opening the chamber. On opening the chamber, immediately close the LOD Bottle, transfer it to desiccator and bring it to room temperature. Weigh up to constant weight.  

                                            W2 – W1
           % Loss on Drying = --------------- X 100
                                            W2 – W3
W1 = Weight of empty clean and dried LOD Bottle.
W2 = Weight of LOD Bottle + sample.
W3 = Weight of LOD Bottle + sample. (After drying)
5. Assay
Limit: 95.5 to 97.0% on as is basis.
Reagents Required:
1.0M Sulfuric acid
0.05M Iodine
Weigh accurately about 0.1gm of sample and dissolve in a mixture of 100 ml freshly boiled and cooled water and 25ml of 1M sulfuric acid. Immediately Titrate with 0.05M iodine, using starch solution as indicator until a persistent blue-violet color is obtained. Each ml of 0.05M iodine is equivalent to 0.008806gm of ascorbic acid.
                                     BR X Actual molarity X 0.008806 X 100
% of Ascorbic acid =  ----------------------------------------------------
                                                         0.05 X Wt. of sample
BR= Burette Reading
6. Foreign particles
Free from foreign particles
Weight about 5 gm of sample and spread on a white paper & observe visually for black particles. Transfer this sample in a conical flask. Dissolve in about 150 ml of water. Observe the solution visually for any foreign particle in the sample against white & black background. If felt necessary, solution can be filtered through whatman filter No. 41 and observed. Sample passes the test if NMT 2 foreign particles per gm are observed.

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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