[Determination of caftaric acid, p-coutaric acid and fertaric acid in grape juice, peel and seeds by ultra-high performance liquid chromatography-tandem quadrupole mass spectrometry].

An ultra-high performance liquid chromatography-tandem quadrupole mass spectrometry (UPLC-MS/MS) method was developed for the determination of hydroxycinnamoyltartaric esters, such as caftaric acid, p-coutaric acid and fertaric acid in grape juice, peel and seed. The target analytes were separated on a Waters UPLC HSS T3 column (150 mm x 2.1 mm, 1.7 microm) at 35 degrees C with gradient elution at a flow rate of 0.3 mL/min. The grape juice was freeze-centrifuged, the supernatant was diluted with 20% methanol. The grape peel and grape seed samples were extracted with 80% ethanol. The extract was cleaned-up on-line with the analytical column by valve switching technology. The mobile phases were water-acetonitrile (both containing 0.1% formic acid). The identification and quantification were achieved by MS/MS in multiple reaction monitoring (MRM) mode via negative electrospray ionization. As lack of commercial standards, p-coutaric acid and fertaric acid were quantified by caftaric acid equivalent. The developed method showed a good linearity over the range of 25-2 000 microg/L with good correlation coefficient (r2 = 0.998 9). The limit of detection was 0.25 microg/L, and the limit of quantification was 25 microg/L. The average recoveries of caftaric acid were between 97.7%-99.5% and the precisions were within 2.5% at the spiked levels of 250, 750 and 1 200 microg/L. The working solutions were stable for 74 h at room temperature. The results showed that there are significant differences of hydroxycinnamoyltartaric esters distribution in grape juice, peel and seeds. Therefore, this method, owing to its simplicity, rapidity, good recovery, high sensitivity and accuracy, can be used for the analysis of caftaric acid, p-coutaric acid and fertaric acid in grape juice, peel and seeds.