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目前利用褪色反应测铬的光度分析法大多灵敏度不高。通过研究三氯偶氮氯膦与Ｃｒ２Ｏ２－７的褪色反应，发现其在硝酸介质中具有高灵敏的褪色反应，其摩尔吸光系数ε＝１．１×１０５，是目前测铬的最灵敏的方法之一。研究发现该体系在５５０ｎｍ处具有最大吸光度ΔＡ，在硫酸、盐酸介质中加热３０ｍｉｎ时褪色不明显，在硝酸介质中加热１０ｍｉｎ已褪色完全。在ＨＮＯ３（Ｖ（ＨＮＯ３）∶Ｖ（Ｈ２Ｏ）＝１∶３）用量为３．０～５．５ｍＬ，０．５ｇ／Ｌ三氯偶氮氯膦溶液的用量为２．０～３．５ｍＬ，沸水浴加热８～１１ｍｉｎ时，褪色完全。本研究选取ＨＮＯ３４．５ｍＬ（Ｖ（ＨＮＯ３）∶Ｖ（Ｈ２Ｏ）＝１∶３），三氯偶氮氯膦溶液２．５ｍＬ，沸水浴加热９ｍｉｎ。Ｃｒ（Ⅵ）质量浓度在０～０．４８μｇ／ｍＬ内符合比耳定律，回归方程为ΔＡ＝０．９７２５ρ（μｇ／ｍＬ）＋０．０１７３，相关系数γ＝０．９９６８。对１８种共存离子的干扰进行了测定，Ｆｅ２＋，Ｆｅ３＋，ＭｎＯ－４的干扰可在溶样时除去。用于合金钢及水中的微量铬的测定结果令人满意。
At present, most of the photometric methods for the determination of chromium by fading reaction are not high sensitivity. By studying the fading reaction of trichloro-chlorophosphonazo with Cr2O2-7, it was found that it has a highly sensitive fading reaction in nitric acid medium. The molar absorptivity ε = 1.1 × 105, which is the most sensitive method for the determination of chromium one. The study found that the system has a maximum absorbance ΔA at 550nm, fading is not obvious when heated in sulfuric acid, hydrochloric acid medium for 30min, fading completely in nitric acid medium for 10min. The dosage of HNO3 (V (HNO3): V (H2O) = 1: 3) was 3.0-5.5mL, the dosage of 0.5g / L trichloro-chlorophosphonazo was 2.0-3.5mL, Boiling water bath heating 8 ~ 11min, faded completely. In this study, HNO34.5mL (V (HNO3): V (H2O) = 1: 3) and 2.5mL trichloro-chlorophosphonazolate solution were added and heated in boiling water bath for 9min. Beer ’s law was obeyed in the range of 0 ~ 0.48 μg / mL for Cr (Ⅵ). The regression equation was ΔA = 0.9725 ρ (μg / mL) +0.0173. The correlation coefficient γ was 0.9968. The interferences of 18 kinds of coexisting ions were measured. The interferences of Fe2 +, Fe3 + and MnO-4 were removed when samples were dissolved. Determination of trace chromium for alloy steel and water is satisfactory.