SIMULTANEOUS DETERMINATION OF MONOCAFFEOYLQUINIC ACIDS AND CAFFEINE BY REVERSE-PHASE HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY WITH ELUENTS BASED ON PROPANOL-2 AND ETHYL ACETATE (REJECTION OF ACETONITRILE)

Abstract

The purpose of the study is development of conditions for the simultaneous determination of caffeine and three isomers of monocaffeoylquinic acids (esters of caffeic and quinic acids: 3CQA, 4CQA and 5CQA) in coffee using "green" reverse-phase HPLC, in which an expensive and environmentally unfavorable acetonitrile is replaced with ethyl acetate as an organic modifier of mobile phases. An approach which provides comparing the efficiency and selectivity of the substance separation in a wide range of concentrations of organic modifiers of selected eluent systems is proposed. It is shown that the replacement of acetonitrile with propanol-2 or ethyl acetate slightly changes the selectivity of the separation of three isomeric chlorogenic acids, but significantly reduces the relative retention of caffeine due to better solvation of caffeine with an organic modifier. This makes it possible to change the position of caffeine elution relative to chlorogenic acids in a targeted way to avoid coelution of caffeine with other extractive substances by changing the concentration and type of the organic modifier of the mobile phase. Ethyl acetate-based eluents are shown to be convenient for simultaneous determination of caffeine and monocaffeoylquinic acids in conditions of reverse-phase HPLC. The replacement of acetonitrile with ethyl acetate makes it possible to re-extract mainly caffeine and monocaffeoylquimc acids from concentrating cartridges (DIAPAK C18) during sample preparation. More lipophilic extractive substances still remain on the concentrating cartridge, which provides the possibility of using a simple isocratic mode thus reducing the duration of analysis and consumption of the organic modifier of the mobile phase.