三氯化钒还原-分光光度法测定海水中硝酸盐的含量

Determination of Nitrate in Seawater by Vanadium Trichloride Reduction-Spectrophotometry

为解决铜镉柱还原法在测定海水中硝酸盐时的操作繁琐、耗时、毒性大、难以适应大批量样品的快速测定等问题,提出了题示方法。取5 mL样品(海水样品用水稀释至盐度不大于7)和1 mL还原剂(体积比5∶1∶1的10 g·L^(-1)三氯化钒溶液、40 g·L^(-1)磺胺溶液和1.0 g·L^(-1)盐酸萘乙二胺溶液的混合溶液)于10 mL试管中,于45℃的水浴锅中加热60 min,取出,置于冰水混合物中冷却5 min,在543 nm波长下测定体系的吸光度差值。结果表明:方法的硝酸盐还原率在95%以上;当样品盐度不大于7时,基本消除盐效应对测定的影响,可用于淡水和海水中硝酸盐的测定。硝酸盐的质量浓度在300.0μg·L^(-1)以内与对应的吸光度差值呈线性关系,检出限为1.0μg·L^(-1)。对50.0,200.0μg·L^(-1)的加标样品溶液进行准确度和精密度试验,测定值与已知值基本一致,测定值的相对标准偏差(n=10)小于0.50%。采用本方法与HY/T 147.1-2013测定实际海水样品,两种方法的测定结果具有一致性,不存在显著性差异。本方法降低了试剂对环境的污染,避免了铜镉柱制备和过柱操作,可用于海水中硝酸盐的快速、批量测定。

To solve the problems of complex operation,time-consuming,high toxicity,and difficulty in adapting to rapid determination of large quantities of samples in the determination of nitrate in seawater by copper cadmium column reduction method,a method mentioned by the title was proposed.5 mL of sample(seawater sample diluted with water to salinity not greater than 7)and 1 mL of reducing agent(a mixed solution of 10 g·L-1 vanadium trichloride solution,40 g·L-1 sulfonamide solution,and 1.0 g·L-1 aphthalene ethylenediamine hydrochloride solution at volume ratio of 5∶1∶1)were taken in 10 mL-tube,and the mixture was heated in water bath at 45℃for 60 min,and then removed to cool for 5 min in ice-water mixture.The absorbance difference of the system was determined at 543 nm.It was shown that the nitrate reduction rate of this method was above 95%;and when the sample salinity was not above than 7,the influence of salt effect on determination was eliminated,and this method could be used for determination of nitrate in fresh water and seawater.Linear relationship between mass concentration of nitrate and its corresponding absorbance difference was kept within 300.0μg·L-1,with detection limit of 1.0μg·L-1.Tests for accuracy and precision were made on the 50.0 and 200.0μg·L-1 spiked sample solution,respectively,giving results that the determined values were basically consistent with the known values,with RSDs(n=10)of the determined values less than 0.50%.This method and HY/T 147.1-2013 were used to determine actual seawater samples.The results of two methods were consistent,and there was no significant difference between two methods.This method reduced the environmental pollution caused by reagents,and avoided the preparation of copper cadmium column and column passing operations,which could be used for rapid and batch determination of nitrate in seawater.