１引言二氧化氯（ＣｌＯ２）是广谱杀菌消毒剂，空气或水中百万分之几的ＣＯ２，即可发挥作用．在多种测定方法中褪色光度法较简便易行，国外报道该类方法检测下最低达０．０１ｍｇ／Ｌ，最宽线性范围为０～２ｍｇ／Ｌ．本文研究了中性红的褪色反应，所建立的光度法其检测下限 1 Introduction Chlorine dioxide (ClO2) is a broad-spectrum bactericidal disinfectant that functions in parts per million by air or water. In a variety of determination methods fading spectrophotometry is relatively simple and easy, the foreign reports of such methods detection as low as 0.01mg / L, the most wide linear range of 0 ~ 2mg / L. This paper studies the neutral red fading reaction, the established photometric method of its detection limit