Assay

Summary of USP Sodium Chloride Assay

The assay for Sodium Chloride determines the actual percentage of NaCl in the sample. According to the USP monograph, Sodium Chloride must contain not less than (NLT) 99.0% and not more than (NMT) 100.5% of NaCl, calculated on a dried basis.

Procedure: Potentiometric Titration

The assay utilizes a silver nitrate titration with a potentiometric endpoint detection.

Step-by-Step Instructions

Preparation: Accurately weigh approximately 50 mg of the Sodium Chloride sample (previously dried).
Dissolution: Dissolve the sample in 50 mL of purified water in a suitable beaker.
Setup: Set up a potentiometric titration apparatus with a silver/silver chloride or suitable electrode system.
Titration: Titrate the solution with 0.1 N Silver Nitrate Volumetric Solution (VS).
Endpoint: Determine the endpoint potentiometrically (the point of maximum change in potential per unit volume of titrant).

Calculation

Each mL of 0.1 N Silver Nitrate is equivalent to 5.844 mg of sodium chloride (NaCl).

% NaCl = (V * N * F * 100) / W
Where:
V = Volume of AgNO3 consumed (mL)
N = Actual Normality of AgNO3
F = Equivalent factor (58.44)
W = Weight of sample (mg)

Tips and Cautions

Category	Guidance
Standardization	Ensure the 0.1 N Silver Nitrate VS is freshly standardized against a primary standard like sodium chloride.
Electrode Care	Clean the silver electrode between titrations to ensure a sharp potential break at the endpoint.
Sample Drying	The assay must be calculated on a "dried basis," meaning the sample should be dried at 105°C for 2 hours before weighing.