用氟离子电极测定土壤溶液中无机单核铝的实验验证

EXPERIMENTAL VERIFICATION OF FLUORIDE ELECTRODE PROCEDURE FOR CHARACTERIZATION OF INORGANIC MONOMERIC ALUMINUM SPECIES IN SOIL SOLUTIONS

本文在Al-F体系中,验证了氟离子电极直接电位法测定和区分溶液中无机单核铝结果的可靠性.研究结果表明,氟离子电极直接电位法测定结果的相对误差在±5%以内.在非25℃条件下,采用校正温度影响的平衡常数进行计算,结果与25℃条件下无明显差别.对于我国南方大多数中等及其以下强度的酸性土壤,可以用氟离子电极直接电位法测定和区分土壤溶液中的无机单核铝.但对强酸性土壤,由于溶液中Al/F比发生了改变,溶液中游离氟离子的活度低于氟电极的检测下限,不宜使用直接电位法.从采自我国南方的几种酸性土壤的测定结果看,中等及其以下强度酸性土壤的溶液中,Al-F络合物是无机单核铝的主要形态.

The reliability of fluoride electrode direct potentiometry for characterization of inorganic monomeric aluminum in Al-F system was verified and the feasibility of this method used for soil solutions was studied. The results indicated that the relative error for this method is within the range of ±5%. If the equilibrium constants corrected for effect of temperature were used in equilibrium calculations at the temperature other than 25℃, the results will be not different from that at 25℃. For most acid to weak acid soils in south of China, it is feasible to use this procedure to characterize the inorganic monomeric aluminum. But this procedure is not suitable for strongly acid soils (pH< 4. 5), because the fluoride activity in soil solutions is lower than the detection limit of fluoride electrode due to the Al/F ratio changes with soil pH. The results from some acid soils in south of China indicated that the Al-F complexes in acid to weak acid soil solutions were major inorganic monomeric aluminum.