Sodium Propionate

(Ph Eur monograph 2041)

C3H5NaO2       96.1 137-40-6

 

Ph Eur


 

 

DEFINITION

 

Sodium propanoate.

 

Content

 

99.0 per cent to 101.0 per cent (dried substance).

 

CHARACTERS

 

Appearance

 

Colourless crystals or white powder, slightly hygroscopic.

 

Solubility

 

Freely soluble in water, sparingly soluble in alcohol, practically insoluble in methylene chloride.

 

IDENTIFICATION

 

First identification

 

A, D.

 

Second identification

 

B, C, D.

 

A.    Infrared absorption spectrophotometry (2.2.24).

 

Comparison: Ph. Eur. reference spectrum of sodium propionate.

 

B.    Dissolve 0.1 g in a mixture of 2 ml of copper sulphate solution R and 2 ml of methylene chloride R. Shake vigorously and allow to stand. Both the upper and the lower layer show a blue colour.

 

C.    To 5 ml of solution S (see Tests) add 2 ml of 0.1 M silver nitrate. A white precipitate is formed.

 

D.    Solution S gives reaction (a) of sodium (2.3.1).

 

TESTS

 

Solution S

 

Dissolve 10 g in carbon dioxide-free water  R prepared from distilled water  R and dilute to 100 ml with the same solvent.

 

Appearance of solution

 

Solution S is clear  (2.2.1) and colourless (2.2.2, Method II).

 

pH (2.2.3)

 

7.8 to 9.2.

 

Dilute 1 ml of solution S to 5 ml with water  R.

 

Related substances

 

Liquid chromatography (2.2.29).

 

Test solution

 

Dissolve 0.250 g of the substance to be examined in water  R and dilute to 100 ml with the same solvent.

 

Reference solution (a)

 

Dissolve 10 mg of the substance to be examined and 10 mg of sodium acetate R in water  R and dilute to 100 ml with the same solvent.

 

Reference solution (b)

 

Dilute 1.0 ml of the test solution to 100 ml with water  R.

 

Column:

size: l = 0.25 m, Ø = 4.6 mm,

 

stationary phase: octadecylsilyl silica gel for chromatography R (5 µm).

 

Mobile phase

 

Dilute 1 ml of phosphoric acid R to 1000 ml with water  R.

 

Flow rate

 

1 ml/min.

 

Detection

 

Spectrophotometer at 210 nm.

 

Injection

 

20 µl.

 

System suitability

 

Reference solution (a):

 

resolution: minimum 5 between the peaks due to sodium acetate and sodium propionate.

 

Limits:

any impurity: not more than 0.1 times the area of the principal peak in the chromatogram obtained with reference solution (b) (0.1 per cent),

 

total: not more than half the area of the principal peak in the chromatrogram obtained with reference solution (b) (0.5 per cent),

 

disregard limit: 0.05 times the area of the principal peak in the chromatogram obtained with reference solution (b) (0.05 per cent).

 

Readily oxidisable substances

 

In a ground-glass-stoppered conical flask introduce 10 g of the substance to be examined. Add 100 ml of water  R and stir to dissolve. Add 25 ml of sodium hypobromite solution R and 10 ml of a 200 g/l solution of sodium acetate R, stopper the flask and allow to stand for 15 min. Add 10 ml of potassium iodide solution R and 20 ml of hydrochloric acid R while cooling. Titrate with 0.2 M sodium thiosulphate, adding 2 ml of starch solution R towards the end of the titration. Carry out a blank titration. The difference between the volumes used in the 2 titrations is not greater than 2.2 ml.

 

Iron (2.4.9)

 

Maximum 10 ppm.

 

10 ml of solution S complies with the limit test for iron.

 

Heavy metals (2.4.8)

 

Maximum 10 ppm.

 

12 ml of solution S complies with limit test A. Prepare the standard using lead standard solution (1 ppm Pb) R.

 

Loss on drying (2.2.32)

 

Maximum 0.5 per cent, determined on 1.000 g by heating in an oven at 100C105 C for 3 h.

 

ASSAY

 

Dissolve 80.0 mg in 30 ml of anhydrous acetic acid R. Titrate with 0.1 M perchloric acid, determining the end-point potentiometrically (2.2.20).

 

1 ml of 0.1 M perchloric acid is equivalent to 9.61 mg of C3H5NaO2.

 

STORAGE

 

In an airtight container .

 

 


Ph Eur

 

Action and use

 

Antifungal.