降低总氮测定中空白吸光值的研究

Study on methods of decreasing blank absorbency in determination of total nitrogen in water

就碱性过硫酸钾消解紫外分光光度法测定总氮时空白吸光值过高的现象进行了研究,确定蒸馏水和K2S2O8纯度是影响试验结果的关键因素。选用普通蒸馏水双蒸去离子后的高纯水及纯度大于99.0%的进口K2S2O8或国产分析纯K2S2O8二次重结晶配制成的溶液,其余步骤参照国标介绍的方法,即可保证空白吸光值小于0.030。当蒸馏水和K2S2O8纯度不高时,适当改进试验的操作过程,如对所配碱性K2S2O8溶液加微量HCl(1+9)处理、延长消解时间至50 min、消解完取出比色管后迅速冷却等方法也可适当降低空白吸光值,但不能确保在0.030以下。消解仪器与分光光度计的不同对分析结果无显著影响。

The blank absorbency is always too high to obtain the exact result when we analyze the total nitrogen using alkaline potassium persulfate digestion-UV spectrophotometric method. We studied the phenomenon and the results were as follows. The purity of water and potassium persulfate was the most essential factor in the analysis. Water with high purity and imported K2S2O8 with the purity of more than 99.0% could insure the blank absorbency less than 0. 030. Instead of using imported K2S2O8, we also obtained perfect results using domestic K2S2O8（AR） as long as we made the reagent secondarily crystallized. If the purity of water or the reagent of K2S2O8 was not high enough, we could improve the experimental operation to reduce the blank absorbency by adding HCI（ 1 ＋9）solution into alkaline potassium persulfate solution, extending the digestion time to 50 minutes or cooling rapidly after digestion. But these methods could only reduce the blank absorbency to some degree but couldn＇ t ensure an absorbency less than 0. 030. Different instruments for digestion or absorbency analysis showed no significant effect on the results.