Purification and spectroscopic properties of pyrene fatty acids

Pyrene fatty acids are routinely purified by silica based column chromatography and analyzed on thin-layer silica plates (H.-J. Galla et al., Chem. Phys. Lipids, 23 (1979) 239-251). Although pyrene decanoic acid runs as a single spot on thin-layer chromatography (TLC), gas-liquid chromatography (GC) of the methyl ester derivatives of a representative sample revealed four separate peaks with the major component only 92% of the total. High performance reverse phase liquid chromatography (HPLC) was used to purify pyrene decanoic acid and separate the contaminants. After two passes on a C18 reverse phase HPLC column, pyrene decanoic acid is 99.98% pure by GC analysis. Absorption, fluorescence, and NMR spectra were recorded for pyrene decanoic acid and the major impurities. The results indicate that one impurity is a C10 fatty acid with an altered aromatic moiety. Two other impurities are pyrene derivatives but their acyl chains probably are not decanoic acid.