KF置换-酸量法测定农业土壤中可溶性铝

研究了测定农业土壤中可溶性铝的酸量滴定新方法.样品经湿法消解,在掩蔽干扰后的pH 7-8的滤液中,用稀NaOH溶液将Al3沉淀为Al(OH)3,加入KF,反应置换出的KOH溶液,以酚酞为指示剂,用酸标准溶液进行滴定.测定结果的相对标准偏差小于2.5%,其加标回收率在95.2%～101.3%之间.结果表明,改进后的方法,具有操作简单、测定快捷、准确度高、干扰小等特点,测定结果与国家标准方法一致.

Determination of Soluble Aluminum in Agricultural Soils by KF Replacing-Acid Titration

A new acid titration method for the determination of soluble aluminum (Al) in agricultural soils was introduced in this paper. The sample was wet-digested and eliminated disturbance at pH 7～8 in filtrates,the A1(OH)_3 was obtained by adding NaOH in filtrate,then the content of Al which had been replaced by adding KF in A1(OH)_3 to KOH was tittered with HC1 in phenolphthalein indicator system. The results showed that its relative standard deviation was less than 2.5% and recovery was 95.2%~101.3% which indicated the modified method was simple,accurate and rapid with good reproducibility. The result was also consistence with the national standard.