Abstract: An analytical method for the determination of 11 water-soluble organic acids (lactic acid, fumaric acid, malic acid, tartaric acid, coumaric acid, gallic acid, citric acid, vanillic acid, ferulic acid, and neochlorogenic acid) in plants by online solid-phase extraction (SPE) coupled with high performance liquid chromatography-quadrupole orbitrap high resolution mass spectrometry (HPLC-Q-Orbitrap-HRMS) was developed. Samples were homogenized, ultrasonically extracted, filtrated, diluted, and purified on an Oasis MAX column (20 mm × 2.1 mm, 30 μm). The analytes were separated on separated on a BEH C18 AX column (100 mm × 2.1 mm, 1.7 μm) by gradient elution using a mobile phase consisting of 0.9% formic acid solution containing 10 mmol/L ammonium formate and 0.9% formic acid in acetonitrile. The MS analysis was performed by full MS/dd-MS2 scanning in the negative ion mode. Quantitation was performed using the internal standard method. Under the optimum conditions, the 11 organic acids were well separated within 9 minutes, and the accurate mass deviation for each compound was less than 5.00 × 10-6. The developed method showed good linearity in the range of 1–100 μg/L with correlation coefficients (R2) greater than 0.999. The limits of detection (LOD) and quantification (LOQ) ranged from 0.1 to 3.2 μg/kg and from 0.3 to 9.6 μg/kg, respectively. The average recoveries of the 11 organic acids in Euryale ferox seeds and pakchoi spiked at two concentration levels were 92.2%–111% and 94.2%–110% with intraday relative standard deviations (RSDs) of 1.4%–4.9% and 0.8%–5.6%, respectively. The method was successfully applied to the analysis of organic acids in white radish, carrot, potato, pakchoi, banana, pear, grape, and E. ferox seeds. This method is simple, fast, accurate, and reliable, and can be used as a new approach for the rapid analysis of water-soluble organic acids in plants.

Key words: organic acids; online solid-phase extraction; high performance liquid chromatography; high resolution mass spectrometry; plants