Edition: BP 2025 (Ph. Eur. 11.6 update)
Diethylamine Salicylate Cream
General Notices
DEFINITION
Diethylamine Salicylate Cream is a dispersion of Diethylamine Salicylate in a suitable basis.
The cream complies with the requirements stated under Topical Semi-solid Preparations and with the following requirements.
Content of diethylamine salicylate, C11H17NO3
95.0 to 105.0% of the stated amount.
IDENTIFICATION
A. To 5 g add 50 mL of 2M sodium hydroxide, shake well and filter. Acidify 30 mL of the filtrate with 2M hydrochloric acid, cool and allow to stand. The infrared absorption spectrum of the resulting precipitate, after recrystallisation from water and drying at 105°, Appendix II A, is concordant with the reference spectrum of salicylic acid (RS 316). B. To 5 mL of the filtrate obtained in test A, add 10 mL of water and 0.05 mL of iron(III) chloride solution R1. A deep violet colour is produced.
C. Mix 3 g with 25 mL of chloroform and shake with 20 mL of 0.1M hydrochloric acid. To the acidic layer add 10 mL of 2M sodium hydroxide and boil. Diethylamine vapour is evolved, which turns moist red litmus paper blue.
ASSAY
To a quantity containing 50 mg of diethylamine salicylate add 30 mL of 0.5M sodium hydroxide and 15 mL of ethanol (96%), mix, heat under a reflux condenser for 30 minutes and cool. To the resulting mixture add 20 mL of 1M hydrochloric acid, mix, dilute to 250 mL with water and filter. Shake 15 mL of the filtrate with 25 mL of chloroform for 2 minutes. To 5 mL of the chloroform layer add 10 mL of iron(III) nitrate solution and shake for 5 minutes. Centrifuge the aqueous layer and measure the absorbance at the maximum at 530 nm, Appendix II B, using iron(III) nitrate solution in the reference cell. Calculate the content of salicylate as salicylic acid, C7H6O3, from the absorbance obtained by repeating the operation using 15 mL of a 0.013% w/v solution of salicylic acid in 0.02M hydrochloric acid, beginning at the words ‘Shake 15 mL…’. Each g of salicylic acid is equivalent to 1.530 g of C11H17NO3.
