氢氧化镁共沉淀法测定海水中纳摩尔级活性磷酸盐

Determination of Reactive Phosphate in Nanomolar Level in Sea Water with Mg(OH)_2 Co-precipitation

利用海水中Mg2+与OH-生成沉淀时会共沉淀PO43-的特性,富集海水中PO34-,富集后的Mg(OH)2沉淀用酸溶解,应用磷钼蓝-分光光度法测定。对试剂用量、离心速度及时间、Mg(OH)2溶解用酸种类、H/Mo等实验参数和条件进行了优化。并采用与常规磷钼蓝法介质一致的H2SO4作为Mg(OH)2沉淀溶解用酸,减少混合试剂中H2SO4的比例,提前用于Mg(OH)2沉淀溶解,减少了沉淀溶解时间,提高了检测效率,同时解决了测试介质H/Mo过高的问题。在优化条件下,改进的共沉淀方法的回收率为97.2%～100.9%,空白值为(4.88±0.29)nmol/L;方法检出限为2.42nmol/L。对大洋表层海水活性磷酸盐测定,其相对标准偏差为2.1%～4.8%。

PO34-in seawater was co-precipitation by the formation of brucite [Mg（OH） 2],initiated by the addition of NaOH.The precipitate was collected by centrifugation and dissolved in acidic solution for the determination of soluble reactive phosphorous（SRP） with classical phosphomolybdic method.Based on other previous study,the experimental parameters and conditions,including the volume of reagent,centrifugation speed and time,kinds of acid,H/Mo ratio,were optimized.A part of H2SO4 in mixed reagent was used for dissolved precipitate not only to keep the same medium with following phosphomolybdenum blue procedure,but also to speed greatly precipitate dissolved and reduce the high H/Mo ratio in solution before.Under the optimized conditions,the recoveries,blank and limits of detection of the proposed method were 97.2%-100.9%,（4.88 ±0.29） nmol/L,and 2.42 nmol/L,respectively.The RSDs ranged from 2.1% to 4.8% for the seawater samples.The method had been used to determine the concentrations of phosphate in the upper water（0-200 m） of the Pacific Ocean successfully.