High-Performance Thin-Layer Chromatography Combined with Densitometry for Quantitative Analysis of Phenolic Acids in Complex Mixtures

Protocatechuic acid and caffeic acid in plant extracts, both free and bound as glycosides and ester derivatives, have been determined by HPLC and by HPTLC combined with densitometry. Comparable results were obtained although the HPLC results were somewhat higher. Although traditional isocratic planar chromatography on silica was not successful, multiple gradient development enabled satisfactory separation, and quantitation of the phenolic acids by densitometry.