二苯碳酰二肼光度法测定超基性岩石中三氧化二铬的改进

二苯碳酰二肼光度法是测定微量Cr(Ⅵ)的行业标准方法,以硫酸作为显色介质,酸度要求严格,显色稳定时间短,体系显色后需在10 min～1 h测定完毕,灵敏度较差。本文对标准方法进行改进,将显色介质由硫酸改为磷酸。结果表明,在H3PO4介质中显色剂与Cr(Ⅵ)反应生成的络合物可稳定3 h,方法相对标准偏差(RSD)≤5.25%,加标回收率为99.2%～102.0%,检出限由标准方法的13.6μg/g降至3.8μg/g。建立的方法用于超基性岩标准物质分析,相比于标准方法,稳定性、精密度和准确性均有提高。

Improvement in the Determination of Chromic Oxide in Ultramafic Rocks by Diphenylcarbazide Spectrophotometry

Diphenylcarbazide Spectrophotometry is a standard method to measure trace Cr(Ⅵ).However,using H2SO4 as the chromogenic medium has limitations such as a strict sulfuric acid concentration,short stability time of 10-60 min and poor sensitivity.An improvement was made to the diphenylcarbazide spectrophotometric method by replacing sulfuric acid with phosphoric acid as the chromogenic medium.Results indicate that the reaction is stable for 3 h in the phosphoric medium,and the detection limit is reduced from 13.6 μg/g to 3.8 μg/g with a recovery factor of 99.2%-102.0% and RSD≤5.25%.Compared with the routine method,the improved method,when applied to ultramafic rock standard materials demonstrates higher stabilization,precision and accuracy.