On the stability of sesquiterpene lactones in the officinal arnica tincture of the German Pharmacopoeia

An investigation of sesquiterpene lactone content in Arnica tincture (Germa n Pharmacopoeia) after storage for three years at different temperatures (4, +25 and +30 degreesC) was carried out by GC and GC-MS analysis. A decrea se (13, 32 and 37 %, respectively) in the content of the main active compou nds in this preparation, 11 alpha ,13-dihydrohelenalin esters, correlating with storage temperature was found. This change was shown to be caused by a ddition of ethanol to the cyclopentenone structure of these molecules leadi ng to 2-ethoxy-2,3,11,13-tetrahydrohelenalin derivatives.