The most common technique for analysis of drug substances is high performance
liquid chromatography (HPLC) using a variable wavelength detector (UV). Cremophor®
EL (ethoxylated castor oil, CrEL) is a non-ionic emulsifier that is used to assist in the
solubilization of hydrophobic drugs such as the antineoplastic agent, paclitaxel. However,
the molecular weight distribution of CrEL creates difficulties in the analysis of potency
and related substances of hydrophobic drugs via UV detection.
Using a precipitation method, CrEL was selectively removed from the paclitaxel
by pre-treating the injectable dosage form with mercuric chloride and analyzing the
filtered extract by HPLC-UV. The removal of CrEL from the injectable dosage form of
paclitaxel by precipitation with mercuric chloride resulted in a solution that was suitable
to quantitate active and related substances by HPLC-UV. The precipitate was then
characterized by nuclear magnetic resonance, infrared spectrophotometry and x-ray
diffraction to elucidate its mechanism of action. The combination of these analyses
provided sufficient evidence that the complex formed between CrEL and mercuric
chloride is from the coordination of the mercury atom to the ether oxygens present in the
CrEL
