Simultaneous extraction and determination of organic acids in xylem saps by RP-HPLC after solid-phase extraction with smaller particle-sized hydroxyapatite nanocrystals

A simple and reliable RP-HPLC method based on solid-phase extraction with smaller particle sized hydroxyapatite nanocrystals was developed for the simultaneous extraction and determination of oxalic, malic, and citric acids in xylem saps of pokeweed. The smaller particle sized hydroxyapatite nanocrystals exhibited greater surface area and more active sites on the surface, consequently, higher adsorption ability to organic acids, which was proved to be an effective solid-phase extractor for the simultaneous extraction of organic acids in xylem saps. Oxalic, malic, and citric acids were determined by RP-HPLC at the optimum chromatographic conditions after the solid-phase extraction procedure. The accuracy of the method was confirmed with an average recovery ranging between 94.2% and 97.9%, the relative standard deviations (RSD) were less than 2.0%. This method was successfully applied to determine the organic acids in xylem saps of pokeweed.