Use of caproic and cyclohexanecarboxylic acids for determining benzoic and sorbic acids

The possibility of using caproic and cyclohexanecarboxylic acids for determining sorbic and benzoic acids, respectively, was studied. The presence of double bonds in sorbic and benzoic acids decreased significantly their retention times compared with those of their saturated analogs (caproic and cyclohexanecarboxylic acids) on chromatography columns with alkyl substituents. The presence of double bonds had a smaller effect on the retention of the compounds on columns with phenyl and nitrile substituents. Sorbic and benzoic acids could not be separated on chromatographic columns with alkyl substituents if the studied mobile phases [MeOH, 20 mMKH₂PO (pH 3.0) or MeCN, 20 mMKH₂PO₄ (pH 3.0)] were used. However these acids were separated on columns with nitrile and phenyl sorbents. The best separation of the acids was achieved on a Diasphere C10CN column.