Edition: BP 2025 (Ph. Eur. 11.6 update)
DEFINITION
Methyl Salicylate is a cutaneous emulsion. It contains 25% v/v of Methyl Salicylate in Arachis Oil or other suitable fixed oil.
The liniment complies with the requirements stated under Liquids for Cutaneous Application and with the following requirements.
Content of methyl salicylate, C8H8O3
23.0 to 26.5% v/v.
CHARACTERISTICS
The liniment has a characteristic odour.
IDENTIFICATION
In the Assay, the chromatogram obtained with solution (2) shows a peak with the same retention time as that due to methyl salicylate in the chromatogram obtained with solution (1).
ASSAY
Carry out the method for gas chromatography, Appendix III B. using the following solutions in petroleum spirit (boiling range, 80° to 100°).
(1) 4% w/v of the preparation being examined and 1% w/v of benzyl alcohol (internal standard).
(2) 4% w/v of the preparation being examined.
(3) 1% w/v of benzyl alcohol (internal standard) and 1% w/v of methyl salicylate.
CHROMATOGRAPHIC CONDITIONS
(a) Use a glass column (1.5 m × 4 mm) packed with diatomaceous support (60 to 80 mesh) coated with 10% w/w of polyethylene glycol 1540.
(b) Use helium as the carrier gas.
(c) Use isothermal conditions maintained at 110°.
(d) Use an inlet temperature of 110°.
(e) Use a flame ionisation detector at a temperature of 110°.
(f) Inject 1 µL of each solution.
DETERMINATION OF CONTENT
Determine the weight per mL of the liniment, Appendix V G, and calculate the content of C8H8O3, volume in volume, taking the content of C8H8O3 in methyl salicylate to be 100.0% and its weight per mL to be 1.18 g.
