提出预先将试样中NO-3用锌-镉还原法还原为NO-2.对还原反应的条件,诸如氯化钠及氯化镉的浓度、溶液的pH值、金属锌(卷状)的加入量以及还原反应所需时间等,进行了研究和优化.还原所得NO-2在酸性溶液中与磺胺进行重氮化后再与萘乙二胺偶合生成红色偶氮化合物.在其吸收峰543 nm波长处测定其吸光度,据此,在校正曲线上间接地查得试样中NO-3的含量.NO-3质量浓度在0~0.400 mg·L-1范围内遵守比耳定律.方法的检出限(S/N=3)为0.008 mg·L-1,在0.1 mg·L-1的浓度水平进行了测定的精密度试验,计算得到相对标准偏差(n=6)为2.1%.在3个浓度水平上作了回收试验,得出回收率在99%~103%之间.

It was proposed in this paper that NO-3 ion in samples of surface water was preliminarily transformed into NO-2 ion by reduction with zinc metal in a solution of cadmium chloride.The conditions for the reduction reaction,including the concentration of sodium chloride and cadmium chloride in the solution,suitable pH-value of the solution,amount of zinc metal (in the form of rolls) used and time required for quantitative reaction,were studied and optimized.The nitrite ion (NO-2) obtained was then diazotized with sulfanilamide,and the diazotized product was further coupled with naphthalene ethylenediamine to give a red colored azo-compound with its absorption maxima at the wavelength of 543 nm.Amount of NO-3 ion was found indirectly from the standard calibration curve by the absorbance of the colored compound.Beer′s law was obeyed in the range of 0-0.400 mg·L-1 (as NO-3),with a detection limit (S/N=3) of 0.008 mg·L-1.Precision of the method was tested at the concentration level of 0.1 mg·L-1,and value of RSD′s (n=6) found was 2.1%.Test for recovery was performed at 3 different concentration levels,values of recovery obtained were in the range of 99%-103%.