Method of Analysis for Ascorbic Acid

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 the sample. The 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 powder 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.
Procedure: 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 the oven and remove the 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 the desiccator and bring it to room temperature. Weigh up to constant weight.
Calculation
                                  W2 – W1
% Loss on Drying = --------------- X 100
                                  W2 – W3
Where:
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
Procedure: Weigh accurately about 0.1gm of the 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 the 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.
Calculation
                                      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
Procedure: Weight about 5 gm of the 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, the solution can be filtered through Whatman filter No. 41 and observed. The sample passes the test if NMT 2 foreign particles per gm are observed.