(Ph. Eur. monograph 0618)
C6H7KO2 150.2 24634-61-5
Action and use
Antimicrobial preservative.
DEFINITION
Potassium (E,E)-hexa-2,4-dienoate.
Content
99.0 per cent to 101.0 per cent (dried substance).
CHARACTERS
Appearance
White or almost white powder or granules.
Solubility
Very soluble in water, slightly soluble in ethanol (96 per cent).
IDENTIFICATION
First identification: B, D.
Second identification: A, C, D.
A. Ultraviolet and visible absorption spectrophotometry (2.2.25).
Test solution: Dissolve 50.0 mg in water R and dilute to 250.0 mL with the same solvent. Dilute 2.0 mL of this solution to
200.0 mL with 0.1 M hydrochloric acid.
Spectral range 230-350 nm.
Absorption maximum At 264 nm.
Specific absorbance at the absorption maximum 1650 to 1900.
B. Infrared absorption spectrophotometry (2.2.24).
Comparison: potassium sorbate CRS.
C. Dissolve 1.0 g in 50 mL of water R, add 10 mL of dilute hydrochloric acid R and shake. Filter the crystalline precipitate, wash with water R and dry in vacuo over sulfuric acid R for 4 h. The residue obtained melts (2.2.14) at 132 °C to 136 °C.
D. Dissolve 0.2 g in 2 mL of water R and add 2 mL of dilute acetic acid R. Filter. The solution gives reaction (b) of potassium (2.3.1).
TESTS
Solution S
Dissolve 2.5 g in carbon dioxide-free water R and dilute to 50 mL with the same solvent.
Appearance of solution
Solution S is clear (2.2.1) and not more intensely coloured than reference solution Y5 (2.2.2, Method II).
Acidity or alkalinity
To 20 mL of solution S add 0.1 mL of phenolphthalein solution R. Not more than 0.25 mL of 0.1 M sodium hydroxide or 0.1 M hydrochloric acid is required to change the colour of the indicator.
Aldehydes
Maximum 0.15 per cent, expressed as C2H4O.
Dissolve 1.0 g in a mixture of 30 mL of water R and 50 mL of 2-propanol R, adjust to pH 4 with 1 M hydrochloric acid and dilute to 100 mL with water R. To 10 mL of the solution add 1 mL of decolorised fuchsin solution R and allow to stand for 30 min. Any colour in the solution is not more intense than that in a standard prepared at the same time by adding 1 mL of decolorised fuchsin solution R to a mixture of 1.5 mL of acetaldehyde standard solution (100 ppm C2H4O) R, 4 mL of 2- propanol R and 4.5 mL of water R.
Loss on drying (2.2.32)
Maximum 1.0 per cent, determined on 1.000 g by drying in an oven at 105 °C for 3 h.
ASSAY
Dissolve 0.120 g in 20 mL of anhydrous acetic acid R. Titrate with 0.1 M perchloric acid using 0.1 mL of crystal violet solution R as indicator until the colour changes from violet to bluish-green.
1 mL of 0.1 M perchloric acid is equivalent to 15.02 mg of C6H7KO2.
STORAGE
Protected from light.
