Determination of Chloride in Food Grade Sodium CMC

The determination of chloride in food-grade sodium carboxymethyl cellulose (CMC) can be carried out using various analytical methods. Here, I’ll outline a commonly used method, which is the Volhard method, also known as the Mohr method. This method involves titration with silver nitrate (AgNO3) solution in the presence of potassium chromate (K2CrO4) indicator.

Here’s a step-by-step procedure for the determination of chloride in food-grade sodium CMC using the Volhard method:

Materials and Reagents:

1. Sodium carboxymethyl cellulose (CMC) sample
2. Silver nitrate (AgNO3) solution (standardized)
3. Potassium chromate (K2CrO4) indicator solution
4. Nitric acid (HNO3) solution (dilute)
5. Distilled water
6. 0.1 M Sodium chloride (NaCl) solution (standard solution)

Equipment:

1. Analytical balance
2. Volumetric flask
3. Burette
4. Erlenmeyer flask
5. Pipettes
6. Magnetic stirrer
7. pH meter (optional)

Procedure:

1. Weigh accurately about 1 gram of the sodium CMC sample into a clean and dry 250 mL Erlenmeyer flask.
2. Add about 100 mL of distilled water to the flask and stir until the CMC is completely dissolved.
3. Add a few drops of potassium chromate indicator solution to the flask. The solution should turn faint yellow.
4. Titrate the solution with standardized silver nitrate (AgNO3) solution until a reddish-brown precipitate of silver chromate (Ag2CrO4) just appears. The endpoint is indicated by the formation of a persistent reddish-brown precipitate.
5. Record the volume of AgNO3 solution used for titration.
6. Repeat the titration with additional samples of the CMC solution until concordant results are obtained (i.e., consistent titration volumes).
7. Prepare a blank determination using distilled water instead of the CMC sample to account for any chloride present in the reagents or glassware.
8. Calculate the chloride content in the sodium CMC sample using the following formula:

Where:

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  V = volume of AgNO3 solution used for titration (in mL)

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  N = normality of AgNO3 solution (in mol/L)

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  M = molarity of NaCl standard solution (in mol/L)

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  W = weight of the sodium CMC sample (in g)

Note: The factor
$35.45$

35.45 is used to convert the chloride content from grams to grams of chloride ion (
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Cl−).

Precautions:

1. Handle all chemicals with care and wear appropriate personal protective equipment.
2. Ensure all glassware is clean and dry to avoid contamination.
3. Standardize the silver nitrate solution using a primary standard such as sodium chloride (NaCl) solution.
4. Perform the titration slowly near the endpoint to ensure accurate results.
5. Use a magnetic stirrer to ensure thorough mixing of the solutions during titration.
6. Repeat the titration to ensure the accuracy and precision of the results.

By following this procedure, you can determine the chloride content in food-grade sodium carboxymethyl cellulose (CMC) accurately and reliably, ensuring compliance with quality standards and regulatory requirements for food additives.