水体总氮测定影响因素的优化研究

On the factors affecting the total nitrogen test for water quality

氮超标是水体富营养化的原因之一,因此总氮质量浓度是水质监测的重要指标之一。但由于在实际分析过程中容易产生空白值偏高、拟合曲线线性差等问题,对试验的操作要求比较严格。通过对比试验和数据分析,对过硫酸钾氧化-紫外分光光度法(GB 11894—89)的试验条件进行了优化。结果表明,在标准分析方法的基础上,延长加热氧化时间至55 min,消解之后,自然冷却2 h,比色时间30 min,可得到更为准确的校准曲线。

The paper is engaged in a research on the factors affecting the total nitrogen test for water quality. As is known, one of the main factors affecting water quality monitoring is that the total nitrogen con- centration exceeds the maximum value, which makes it necessary to test and determinate the total nitrogen content in the water body. But in the practical analysis of water body, problems often come aboutwith the poor linearity of the fitted curve and the accuracy of determi- nation of the total nitrogen, in addition to the higher blank value than required by the system error due to the improper selection of the oper- ational conditions. Sometimes even the total nitrogen concentration is lower than that of ammonia nitrogen as is required as the national standard for the same water sample. It is for all the above reasons that the experimental conditions and parameters should be chosen as accurately as possible in determining the total nitrogen of the water bodies. For all the above needs, we have optimized the primary in- fluential factors, such as the purity degree of potassium persulfate, the purity degree of the experimental water, the slacking time of the alkaline potassium persulfate solution, the preparation method, and so on. At the same time, we have also improves the experimental en- vironmental conditions, the cooling time of the digestion process, and the method of the alkalinity potassium persulfate oxidation digestion, known as the UV spectrophotometer （GB 11894--1959） through con- trastive experiments in an environment with no ammonia as a con- stituent part. The results of our experiments indicate that, it is possi- ble to obtain more accurate calibrated curve and more precise experi- ment results, if the digestion temperature could be kept between t23 ~C and 124 ℃, and the deposited time of potassium persulfate could be made to last for 55 minutes, with the cooling time till 2 hours after heating, and the colorimetric time being 30 minutes. Be- sides, the purity of potassium persulfate should be done through sec- ondary recrystallization. And, the configuration of the alkaline potas- sium persulfate solution should be done separately, with the solution temperature of potassium persulfate kept within the limit of 60 ℃ .