Separation and Identification of Some Monomeric and Dimeric Phenolic Acids by a Simple Gas Chromatographic Method Using a Capillary Column and FID-MSD

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Abstract
The monomeric and dimeric phenolic acids represent highly various structural substance classes. Included among the monomers are substituted benzoic acid, phenylacetic acid, phenylpropionic acid, and cinnamic acid; compounds of the biphenyl and cyclobutane types are representatives of dimeric acids. The formation of dimeric acids with a diphenylcyclobutane dicarboxylic acid structure from t-p-coumaric acid (t-p-CA) and t-ferulic acid (t-FA) via a [2+2]-photocycloaddition reaction is thoroughly described. The products are characterized by using mass spectroscopy and by observing their chromatographic behavior. The applied method makes it possible to determine over 50 phenolic acid isomers. The following elution sequence for the monomeric acids is found: benzoic acids < phenylacetic acids < phenylpropionic acids < cinnamic acids. Among the dimeric acids, which appeared significantly after the monomeric acids, those with a diphenylcyclobutane dicarboxylic acid structure elute before cis/trans-dehydrodiferlic acid (c-t-DFA).