Evaluation of supercritical fluid chromatography for testing of PEG adducts in pharmaceuticals

Drug formulations containing polyethylene glycol may give rise to formation of reaction products between the aforementioned and the active pharmaceutical ingredient. Supercritical fluid chromatography has recently achieved new interest and improved instrumentation is now available. Here, supercritical fluid chromatography has been evaluated for its possible use for determination of reactions products formed between polyethylene glycol and active pharmaceutical ingredients. A mixture of polyethylene glycols with average molecular weights of 400-6000Da was separated with supercritical fluid chromatography using silica columns and carbon dioxide modified with methanol as mobile phase. Satisfactory resolution (Rs=1.2) of the individual oligomers up to a molecular weight of 1000Da was obtained using evaporative light scattering as detection technique. The active pharmaceutical ingredients, cetirizine or indomethacin were investigated in a reaction mixture containing polyethylene glycol 400 after incubation at 80°C for 120h. Polyethylene glycol esters formed upon reaction with both active pharmaceutical ingredients were observed as polymeric patterns with ultraviolet detection and identified with mass spectrometry. Cetirizine was observed to be more reactive than indomethacin. The observed difference in reactivity is due to differences in polar and steric effects between cetirizine and indomethacin. Evaporative light scattering, ultraviolet absorbance and mass spectrometric detection were investigated and each detection technique has its own advantages and disadvantages, but in order to be able to detect selected impurities in the complex mixture of impurities formed, mass spectrometry is superior.