在pH8.2的二乙三胺五乙酸-三羟甲基氨基甲烷(DTPA-Tris)缓冲介质中,通过紫外光照射使NO-3还原为NO-2后,与显色剂反应生成吸收峰位于540 nm波长处的化合物,据此提出了在线紫外光照还原流动注射分光光度法测定海水中硝酸盐。经试验,选择30 g·L-1氯化钠溶液作为载流,所选定的反应圈及样品环的长度依次为180 mm和130 mm。硝酸盐的质量浓度在0.009~3.0 mg·L-1范围内与相应的吸光度呈线性关系,其检出限(3s/k)为4.63 μg·L-1。对同一天然海水样品按此法测定其NO-3含量10次,测得其平均值为0.538 mg·L-1,相对标准偏差为0.34%,并求得NO-3的还原率为80%。另在6个海水样品中各加0.50 mg·L-1 NO-3标准溶液,按方法做回收试验,测得其回收率在97%以上。

In a DTPA-Tris buffer medium of pH 8.2, NO-3 was reduced to NO-2 by UV irradiation reduction, and a colored product with its absorption maximum at the wavelength of 540 nm was formed by its reaction with the color reagent. Based on these facts, a FI-spectrophotometric method with on-line UV irradiation reduction for determination of NO-3 in seawater was proposed. 30 g·L-1 NaCl solution was used as carrier. The lengths of reaction coil and sampling ring chosen were 180 mm and 130 mm respectively. Linearity was kept between values of mass concentration of NO-3 and the corresponding absorbances in the range from 9×10-3 to 3.0 mg·L-1, with the detection limit (3s/k) of 4.63 μg·L-1. In analyzing a natural seawater sample for 10 determinations, an average concentration of NO-3 of 0.538 mg·L-1 was obtained with RSD of 0.34%. The reduction rate of NO-3 was found to be 80%. Recovery was tested by addition of 0.50 mg·L-1 of NO-3 standard solutions to each of 6 seawater samples, values of recovery found were more than 97%.