用自动热滴定法测定土壤中的硫酸盐

在测定土壤中的硫酸盐的各种方法中,重量法较为费时,使用指示剂的滴定法因难于找到合适的指示剂,不易看出滴定终点。有人用铅离子选择性电极做指示电极,用过氯酸铅进行电位滴定,可以得到较为满意的结果^[2],但因为硫酸铅的溶解度较大,必须加入大量的有机溶剂,这时如果溶液中的钙或氯离子过多,可以引起测定误差或使曲线的转折点不明显。近年来随着热敏电阻的发展,有人^[1,3]用热滴定法测定溶液中的硫酸盐。本文是将热滴定法应用于土壤中硫酸盐测定的初步结果。

DETERMINATION OF SULFATE IN SOIL BY THERMOMETRIC TITRATION METHOD

The applicability of thermometric titration method for the determination of sulfate in soil was studied.A thermistor was used to indicate the temperature change of the tat solution. A constant flow device was used to deliver the barium chloride solution as titrant. The titration curves were recorded automatically by a strip-chart recorder. It is found that the reproducibility of recovery of added sulfate was only about ±10% when thermometric titration method was directly applied to the determination in soil extracts. But in 50% alcohol solutions a reproducibility of about ±4% was obtained. The accuracy as compared with gravimetric method was about ±4%.The minimum content of sulfate which can be measurcd with:reasoaabl a accuracy is 1 meq/100g soil when proportion of soil to water is 1:5.It is concluded that the method has the advantage of rapidness with an accuracy comparable to indirect titration method by EDTA.