The Efficient Extraction of Phenolic Compounds from Oak Gall Using a Miniaturized Matrix Solid-Phase Dispersion Method before their HPLC Determination

Abstract

Background and Aim: Several gall varieties are found in Lorestan Province, Iran, on Quercus infectoria oak trees, which contain important phenolic compounds. In this work, a miniaturized matrix solid-phase dispersion (MSPD) extraction method has been developed for quantitative extraction and HPLC/UV determination of them. Materials and Methods: In the MSPD method, 10 mg of sample and 50 mg of silica gel adsorbent were transferred into an agate mortar. The mixture was finely pulverized after adding 40 µL dichloromethane as disperser solvent. It was then transferred into a cartridge, eluted by 350 µL of methanol, and the eluate was subsequently injected into HPLC for analysisn. Results: The extractions were quantitative with mean recoveries of 103.0±6.8% and 99.5±7.3% for ellagic acid (EA) and gallic acid (GA) in six replicated extractions, respectively. The detection limit of the method was 0.05-0.06 mg g-1. The method was successfully applied to the extraction and HPLC determination of the phenolic compounds in five gall species. Conclusion: The proposed technique is simple and fast. It substantially reduced the amounts of sample, sorbent and organic solvents required for the extraction. The maximum amounts of the phenolic compounds were found in Qalqaf and Bramazu galls.