SOP: Determination of Sodium Chloride in Vinegar

GIFSQ — Global Institute for Food Safety & Quality

Principle

The chloride in the water-soluble ash is determined by argentometric titration: silver nitrate precipitates the chloride, and the end point is shown by the red-brown colour of silver chromate with potassium chromate indicator, or by the Volhard back-titration. The result is expressed as sodium chloride percent (w/v).

Reagents

a. 0.1 N silver nitrate solution.

b. Potassium chromate indicator (for the direct titration).

c. Reagents for the Volhard method (see Chapter 30 of this book).

Procedure

Pipette 50 ml of the filtrate from the water-soluble ash solution (see the ash analysis of vinegar) and titrate with 0.1 N silver nitrate using potassium chromate as indicator to a red-brown end point, or by Volhard’s method

Calculation

Sodium chloride % (w/v) = [(ml of AgNO₃ required ÷ ml of ash solution taken for titration) × Normality of AgNO₃ × 58.5 × (Total volume of ash solution ÷ ml of sample taken for ashing) × 100] ÷ 1000

Where,

• ml of AgNO₃ required = volume of standard silver nitrate used in the titration (ml)
• ml of ash solution taken for titration = volume of the filtrate aliquot titrated (ml)
• Normality of AgNO₃ = normality of the standard silver nitrate solution
• 58.5 = mg of sodium chloride equivalent to 1 ml of 1 N silver nitrate (the print carries a garbled fragment “0-5.” at this position)
• Total volume of ash solution = volume to which the water-soluble ash filtrate was made up (ml)
• ml of sample taken for ashing = volume of vinegar whose ash was taken (ml)

Precautions

• Keep the sample portions and dilutions exactly as prescribed; the formula scales the titration to the whole ash solution and the original sample volume.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.