DEFINITION
Salicylic Acid 120 g
Flexible Collodion Sufficient to produce 1000 mL
The collodion complies with the requirements stated under Liquids for Cutaneous Application and with the following requirements.
Content of salicylic acid, C7H6O3
13.0 to 15.8% w/w.
ASSAY
Dilute 2 g to 200 mL with acetone and to 2 mL of this solution add 35 mL of acetate buffer pH 2.45 and 4 mL of a freshly prepared 0.5% w/v solution of iron(III) chloride hexahydrate. Dilute to 50 mL with acetate buffer pH 2.45, filter, discarding the first 10 mL of the filtrate, and measure the absorbance of the resulting solution at the maximum at 525 nm, Appendix II
B. Calculate the content of C7H6O3 from the absorbance obtained by repeating the operation using 2 mL of a 0.12% w/v solution of salicylic acid in ethanol (96%) and beginning at the words ‘add 35 mL of acetate buffer pH 2.45 …’.
