0.1 N Iodine Solution Preparation as per USP
Introduction
Iodine solution is a commonly used reagent in various pharmaceutical applications, including titrimetric analysis and microbiological testing. The United States Pharmacopeia (USP) provides guidelines for the preparation of 0.1 N iodine solution, which is a standardized solution used as a titrant or indicator in various analytical procedures. This article outlines the preparation of 0.1 N iodine solution as per USP guidelines.
Preparation of 0.1 N Iodine Solution
Materials Required
- Iodine crystals (resublimed, USP)
- Potassium iodide (ACS)
- Distilled water
Preparation
- Dissolve 12.69 grams of iodine crystals in 1 liter of distilled water. This will produce a stock solution with a concentration of approximately 0.1 N.
- Add 20 grams of potassium iodide to the solution. The potassium iodide helps to stabilize the iodine solution and prevents the loss of iodine due to sublimation.
- Stir the mixture until the potassium iodide is completely dissolved.
- Filter the solution through a filter paper or membrane filter to remove any undissolved particles or impurities.
- Dilute the stock solution to the desired volume with distilled water.
Calculations
The normality of the iodine solution can be calculated using the following formula:
Normality (N) = Number of grams of iodine / Equivalent weight of iodine x Volume of solution (L)
where the equivalent weight of iodine is 126.92 g/mol.
Verification of Concentration
The concentration of the 0.1 N iodine solution can be verified by titrating it against a standardized sodium thiosulfate solution. The titration reaction is as follows:
I<sub>2</sub> + 2S<sub>2</sub>O<sub>3</sub><sup>2-</sup> → 2I<sup>-</sup> + S<sub>4</sub>O<sub>6</sub><sup>2-</sup>
The equivalence point of the titration can be determined using a starch indicator, which turns blue-black in the presence of excess iodine.
Storage and Stability
The 0.1 N iodine solution should be stored in a dark glass bottle with a tight-fitting stopper. The solution is stable for at least 6 months when stored at room temperature (20-25°C). However, it is recommended to prepare the solution fresh whenever possible to ensure accuracy and reliability in analytical applications.
Conclusion
In conclusion, the preparation of 0.1 N iodine solution as per USP guidelines involves dissolving iodine crystals and potassium iodide in distilled water, followed by filtration and dilution to the desired volume. The concentration of the solution can be verified by titrating it against a standardized sodium thiosulfate solution. The solution should be stored in a dark glass bottle with a tight-fitting stopper and used within 6 months of preparation.
