水质总氮测定时空白值的影响因素

Influencing Factors of Blank Value in the Determination of Total Nitrogen in Water

目的研究总氮标准曲线上空白值的影响因素,分析不同影响因素对测定结果的影响程度并给出降低空白值的解决方法。方法采用对照方法对消解时间、比色时间、过硫酸钾的纯度、氢氧化钠的纯度、实验用水、玻璃器皿的清洗方式进行对照实验。结果除比色时间外,消解时间、过硫酸钾的纯度、氢氧化钠的纯度、实验用水、玻璃器皿的清洗方式均会造成空白值异常,其中过硫酸钾的纯度对空白值的影响程度最大。实验前所用的玻璃器皿应用(1+9)盐酸溶液酸洗浸泡。选用新鲜的实验用水及优级纯的药剂在121℃、50 min下进行消解,实验效果最佳,空白值可降到0.03以下。结论延长消解时间、使用优级纯的过硫酸钾、改变玻璃器皿的清洗方式、使用新鲜的蒸馏水或去离子水均可有效地降低空白值,达到《水质总氮的测定碱性过硫酸钾消解紫外分光光度法》(HJ636-2012)的要求。

The purpose of this paper is to discuss the factors affecting the blank value of the total nitrogen standard curve,to analyze their impact on the measurement results and to give a solution to reduce the blank value.The control method was used to compare the digestion time,colorimetric time,purity of potassium persulfate,purity of sodium hydroxide,experimental water,and the cleaning method of glassware.In addition to the colorimetric time,the digestion time,the purity of potassium persulfate,the purity of sodium hydroxide,the experimental water,and the cleaning method of glassware may all cause the blank value to be abnormal.Among them,the purity of potassium persulfate has the greatest effect on the blank value.The glassware used before the experiment should be soaked with(1+9)hydrochloric acid solution.Fresh experimental water and excellent pure reagents should be used for digestion at 121℃and 50 min.The experimental results are the bes The blank value can be reduced to less than 0.03.So extending the digestion time,using excellent pure potassium persulfate,changing the cleaning method of glassware,using fresh distilled water or deionized water can effectively reduce the blank value,which meet requirements of“Water quality-Determination of total nitrogen-Alkaline potassium persulfate digestion UV spectrophotometric method”(HJ636-2012).