Comparison of salt titration and potentiometric titration methods for the determination of Zero Point of Charge (ZPC)

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Abstract
The salt titration (ST) method was evaluated as a method to determine ZPC in comparison with the potentiometric titration (PT) method for 26 soils with variable charge clays, i.e., Oxisols and Ultisols from Thailand and Andisols from Japan. In addition to the determination of ST-pH0 as the zero point of charge, a calculation procedure (STPT method) was adopted here in order to acquire more information from the titration curve. Furthermore, for the purpose of cross-checking of ZPC determined by the PT method, the ST procedure was successively applied to the samples analyzed by the PT method (PTST method). The soil to solution ratios of 1: 10 to 1: 5 gave almost an identical ST-pH0 value for every soil. The values of both ST-pH0 and PT-ZPC ranged from 4.7 to 6.3 for the Andisols, while for the Oxisols and Ultisols, they were always below 4.2. The difference between the values of ST-pH0 and PT-ZPC was only slight for the Andisols, whereas it was sometimes large (0.4 pH unit) for the Oxisols and Ultisols. Nevertheless, it was concluded that the ST method with its modification (STPT) was comparable to or even better than the PT method for the soil characterization work due to its convenience and simplicity.