Determination of Organic Acids in Soil with High Performance Liquid Chromatography

Objective The extensive analysis and determination of organic acids in soil or plants are crucial for supporting research on the organic matter turnover and nutrient cycling in terrestrial ecosystems.

Method The optimized method for simultaneously determining 7 organic acids in soil by using High Performance Liquid Chromatography (HPLC) was established through experiments on chromatographic conditions, sample pretreatment and recovery rates of different samples.

Result The method was validated by performing its linearity, recovery and precision. The separation was performed on an AcclaimTM 120 (C₁₈, 5 μm, 4.6 × 250 mm) column at 30°C, 210 nm detection wavelength and isocratic elution with 50.0 mM Na₂SO₄ solution (adjusted to pH 2.65 with methanesulfonic acid) mixed with methanol in a ratio of 98:2 as mobile phase (0.6 mL min⁻¹) and an injection sample’s volume of 5 μL. The chromatographic peaks of the 7 organic acids had asymmetry factors close to 0.95 ~ 1.05 and resolutions greater than 2.5, indicating good chromatographic peak shape and completed separation between two adjacent peaks. The theoretical plate numbers were all above 5000, demonstrating high column efficiency. The recovery rate of the added standard in soils and quartz sands ranged from 71.15% to 109.74%, the relative standard deviations for the blank samples with added standards ranged from 0.95% to 4.68%, while those for the parallel samples ranged from 1.57% to 4.75%, and the correlation coefficients for the calibration curves of all organic acids were greater than 0.999, indicating high precision of the instrument and method.

Conclusion The High-performance Liquid Chromatography (HPLC) method for simultaneous determination of multiple organic acids was suitable for measuring the contents of organic acids in soil.