Analytical Sciences

An Improved Method for the Extraction of Low Molecular Weight Organic Acids in Variable Charge Soils

Xingxiang WANG,* Qingman LI,** Jianhua DING,*** Mingbiao LUO,*** Taolin ZHANG,* and Yiyong ZHOU**

*Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
**Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
***East China Institute of Technology, Fuzhou 344000, China

Due to specific adsorption to variable charge soils, low molecular weight organic acids (LMWOAs) have not been sufficiently extracted, even if common extractants, such as water and 0.1 M sodium hydroxide (NaOH), were employed. In this work, the method for extracting LMWOAs in soils with 0.1 M NaOH was improved for variable charge soils; e.g. 1.0 M potassium fluoride (KF) with pH 4.0 was applied as an extractant jointed with 0.1 M NaOH based on its stronger ability to change the electrochemical properties of variable charge soils by specific adsorption. With the proposed method, the recoveries of oxalic, tartaric, malic, citric and fumaric acids were increased from 83 ± 4, 93 ± 1, 22 ± 2, 63 ± 5 and 84 ± 3% to 98 ± 2, 100 ± 2, 85 ± 2, 90 ± 2 and 89 ± 2%, respectively, compared with NaOH alone. Simultaneously, the LMWOAs in Agri-Udic Ferrosol with field moisture were measured with a satisfactory result.

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