High-performance liquid chromatographic detection of selected phenolic acidsin wine

Abstract

The aim of this study was to develop a method for identification and quantification of phenolic acids in different wine samples. The simple reversed-phase HPLC-UV method for simultaneous determination of p-coumaric and ferulic acid was developed. The method was validated and working range, linearity, repeatability, accuracy, limit of quantitation LOQ and limit of detection LOD were determined. The linearity of the method was tested in concentration ranges 0.1-1 mg L-1 and 1-10 mg L-1. The correlation coefficients (r2) were greater than 0.996 and quality coefficients (QC) ≤ 5%. Detection limit for both compounds was 0.01 mg L-1. The method is precise (RSD<10%) and accurate. Two different wine sorts were used for analysis, Slovene red wine Refošk and Slovene white wine Laški Rizling. The wine samples were ultrasonically extracted with ethyl acetate, centrifuged, evaporated, re-dissolved in mobile phase and filtered. The solution was analyzed directly by HPLC-UV. Phenolic compounds were separated with a C18 reversed-phase column by isocratic elution using 2 % acetic acid in water-methanol (85:12, v/v) as the mobile phase at a flow rate of 0.7 mL min-1. Acids were detected and quantitation was performed at wavelength of 320 nm. Extraction procedure was optimized and yields were calculated from internal standard recovery. O-coumaric acid was used as internal standard. From the results it is evident that the red wine Refošk contains higher concentrations of investigated compounds then the white wine Laški Rizling. Stability tests were performed with standard compounds of p-coumaric and ferulic acid. It was established that both standards occur as trans-isomers, but when they were dissolved in methanol and stored exposed to daylight and room-temperature they were gradually transformed to cis-isomers. All closely related geometrical cis- and trans-isomers were successfully separated under the same conditions as described before. The described method is simple and rapid as it involves liquid extraction with no other pretreatments of samples. It is suitable for simultaneous determination of cis and trans isomers of p-coumaric and ferulic acid in different liquid samples.