硝酸盐含量是水体质量指标之一, 对于水质质量监测尤其重要。 本文搭建了一种水体中硝酸盐在线原位监测系统, 采用紫外吸收光谱法（190～240 nm）计算水样吸光度, 并通过建立的偏最小二乘模型测定硝酸盐浓度, 可用于海洋, 河流, 湖泊等多种水体。 该自动在线监测系统不需要进行水样预处理, 无二次污染, 能够快速, 可靠, 灵敏地直接测定现场水样的硝酸盐含量。 本系统使用光程为1cm的流通式样品池, 并采用参考光路消除系统误差。　将系统测量模型得到的不同水样的硝酸盐浓度值与实验配制浓度值相比较, 结果表明二者的线性拟合曲线的相关系数r为0.999　98, 具有良好的相关性。 对采集的浓度数据进行系统误差分析, 得到其平均相对误差为0.65%, 说明系统精确度高, 并且稳定性很好。 还通过对烟台海岸进行的现场海水测试, 其海水硝酸盐含量约为0.2　mg·L-1左右, 以及在水样加标回收实验中, 加标回收率皆在 95%～110%内, 验证了系统的可靠性和实用性, 可用于实际水体硝酸盐监测。

Nitrate is one of the evaluation indicators of water quality, which is particularly important for water quality monitoring. A real-time on-line monitoring system of nitrate in water is introduced in this paper. And the ultraviolet absorption technology (190～370 nm) with partial least squares method is used to detect nitrate concentration. The automated online system based on ultraviolet absorption spectrum is capable of analyzing samples without any sample preservation and without contamination problems. This system is fast, reliable, and sensitive enough for continuous use on monitoring stations and nitrate concentration can also be determined directly via its ultraviolet absorption spectrum. This system uses flow sample cell with 1cm optical path length, and a reference light is used to eliminate system error. The correlation coefficient for a linear function of the nitrate concentrations is 0.999　98. So the results of the system model test are in good correlation with the laboratory ones. Data collected has been analyzed statistically to determine how system model behave throughout the test, with special attention being paid to error analysis. As the average relative error is 0.65%, this system has greater stability and higher accuracy. The results of nitrate measurements by the field seawater tests in Yantai coast are obtained, which nitrate concentrations are about 0.2　mg·L-1 in seawater, and the recoveries　of samples for standard recovery tests are in 95%～110%, it shows that this system is accurate, reliability and practicability and could be developed for detected nitrate concentration in natural water.