海水中溶解态总氮测定方法比对及影响因素分析

过硫酸钾氧化-锌镉还原法（"锌镉法"）和过硫酸钾氧化-镉铜还原法（"镉铜法"）是我国海水中溶解态总氮测定的常用方法，为比较两种方法之间的差异，本文结合17家实验室海水中溶解态总氮的现场比测结果，对两种方法的测定结果进行比对，并对其影响因素进行分析。不同实验室采用同一方法测定相同样品的对比表明，各实验室内部测定结果具有较好的精密度，实验室之间则表现为锌镉法测定结果波动较大，镉铜法测定结果波动较小的特征；采用两种方法测定同一样品的方法比对表明，锌镉法测定结果低于镉铜法。两种方法的测定结果表明，在同一的实验试剂和实验用水条件下，两种方法测定海水中溶解态总氮的结果波动较大，表明消化瓶内壁吸附的杂质、硝酸盐还原方式以及实验过程中引入的沾污等均是影响测定结果的重要因素。

Method comparison and analysis of influence factors for determination of dissolved total nitrogen in seawater

Persulfate oxidation method is the conventional method for the determination of dissolved total nitrogen in seawater.Based on the different ways of nitrate reduction, persulfate oxidation method can be categorized into two types:zinc-cadmium method and cadmium-copper method.Combined with the results of dissolved total nitrogen in seawater measured by 17 laboratories, the comparison of the determination of dissolved total nitrogen in seawater using these two methods was done, and the influencing factors were discussed.The internal-laboratory results showed good precision, and the inter-laboratory comparison results indicated that the zinc-cadmium method was more fluctuating than the cadmium-copper method.For the same seawater sample, lower values were measured by the zinc-cadmium method compared with the cadmium-copper method.Under the condition of using the same experimental reagents and water, the measured concentrations of dissolved total nitrogen with both methods fluctuated obviously, indicating that the impurities from digestion bottle, the nitrate reduction ways and the contamination introduced during the experiment exerted significant impacts on the results of dissolved total nitrogen determination.