催化动力学分光光度法直接测定天然水体中痕量锰

Determination method of dissolved manganese in natural water by catalytic kinetic spectrophotometry

海水中溶解态痕量元素锰（Mn）是国际GEOTRACES科学计划确定的关键参数之一,通常用作示踪剂探讨海洋中氧化还原环境的变化。本文对高碘酸钠氧化隐色孔雀绿测定海水中溶解态Mn的方法进行了优化,最佳实验条件为：在10 m L体系中,反应p H为4.0±0.2,隐色孔雀绿用量为35μmol/L,高碘酸钠用量为4 mmol/L,氨三乙酸的用量为8 mmol/L,显色时间选择4.0±0.2 h,在615~620 nm处测定反应产物的吸光度。结果表明：本方法不存在其他金属离子的干扰,可通过标准加入的方式去除基体效应。应用本方法对空白和浓度为5.5 nmol/L的样品分析的精密度分别为6.8%和2.7%（n=13）,检出限为0.6 nmol/L（3倍标准偏差）。应用本方法分别测定环境标准样品（GSB 07-1189-2000）和加拿大标准海水样品（NASS-6）,测定值与推荐值无显著性差异（t检验,P=0.95）。运用本方法测定了东海陆架黑潮深水区溶解态Mn的垂直分布,测得的剖面结果与国际已发表同区域结果无显著性差异（t检验,P=0.95）。

Dissolved manganese （Mn） in the ocean is one of the key parameters of international scientific project GEOTRACES, which can be used as a sensitive tracer to discuss the redox variation in the ocean. In this paper, the op- tional conditions for the method of oxidation of leucomalachite green by sodium periodate to determine trace amount of dissolved Mn in natural waters are reported. In 10 mL system,the pH is adjusted to 4.0± 0.2 ,the proper concentrations of leucomalachite green, sodium periodate and nitrilotriacetic acid are 35 μmol/L,4 mmol/L and 8 mmol/L, respectively. The absorbance of Mn is measured at 615 - 620 nm after reaction time of 4.0± 0.2 h. The method reported here is free from ionic interferences, and the matrix effects can be overcome by standard addition. The detection limit of dissolved Mn is 0.6 nmol/L （3 standard deviation） ,with a precision of 6.8% for blank and 2.7% at Mn level of 5.5 nmol/L （ n = 13 ） in routine analysis. The analysis of Chinese environmental reference materials （ GSB 07- 1189-2000） and Canada certified reference seawater material （NASS-6） by the method developed here provide results consistent with the certified values （ t-test, P = 0.95 ）. There is no significant difference of the vertical profile of dissolved Mn in Kuroshio waters of the East China Sea measured by this method compared with the international published results within the same location （t-test, P = 0.95）.