How to Detect Vitamin C in Products

>> USP General Chapter 580: Determination of Vitamin C <<

The following procedures can be used to analyze different forms of Vitamin C, such as ascorbic acid (C₆H₈O₆), sodium ascorbate (C₆H₇NaO₆), and calcium ascorbate dihydrate (C₁₂H₁₄CaO₁₂ · 2H₂O), or mixtures of their finished dosage forms such as capsules, tablets, or oral solutions.

Capsule Sample Solution

Weigh at least 20 capsules in a tared weighing bottle. Open the capsules without losing any shell material and transfer the contents to a 100 mL beaker. If necessary, wash with ether to remove impurities adhering to the empty shells. Discard the wash liquid and dry until the smell of ether is no longer detectable. Discard the wash liquid and dry the capsule shells with the help of a stream of dry air until the smell of ether is no longer detectable. Weigh the empty capsule shells in the tared weighing bottle and calculate the average net weight per capsule. Transfer a portion of the capsule contents equivalent to 100 mg of ascorbic acid to a 200 mL volumetric flask, add 75 mL of phosphoric acid-acetic acid TS, insert the stopper into the volumetric flask, shake mechanically for 30 minutes, and make up to volume with water.

Oral Liquid Sample Solution: Transfer an amount equivalent to 50 mg of ascorbic acid (diluted with water if necessary) of the oral solution to a 100 mL volumetric flask. Add 20 mL of phosphoric acid-acetic acid TS, make up to volume with water, and mix well.

Tablet Sample Solution

Grind at least 20 tablets. Transfer a powder equivalent to 100 mg of ascorbic acid to a 200 mL volumetric flask, add 75 mL of phosphoric acid-acetic acid TS, insert the stopper into the volumetric flask, shake mechanically for 30 minutes, and make up to volume with water.

Blank: A mixture of 5.5 mL of phosphoric acid-acetic acid TS and 15 mL of water.

Titration Analysis: (See USP General Chapter 541 for titration method)

Mode: Direct titration

Titrant: Dichlorophenol-indophenol VS standard solution

Result Detection: Visual

Analysis

Transfer a portion of the sample solution to a centrifuge tube and centrifuge until a clear supernatant is obtained. Transfer a specific volume of the sample solution (equivalent to 2 mg of ascorbic acid) to a 50 mL conical flask and add 5 mL of phosphoric acid-acetic acid TS. Titrate with the titrant until a rose pink color persists for at least 5 seconds. Correct for the volume of titrant consumed by the blank.

Calculate the percentage of ascorbic acid (C₆H₈O₆) in the portion of the sample taken:

Result = {[(VS − VB) × F]/W} × 100

VS = Volume of titrant consumed by the sample solution (mL)

VB = Volume of titrant consumed by the blank (mL)

F = Concentration of the titrant in ascorbic acid equivalents (mg/mL)

W = Nominal weight of ascorbic acid used for analysis (mg)

USP General Chapter 580: Determination Method 1

Products Applied

▲ SCRC Aluminum Foil Stand-Up Pouch