New Method For Rapid Detection Of Chromium (VI) In Water

Hexavalent chromium ( Cr⁶⁺ ), in animals and plants, has serious adverse effects. It is important to determination and monitoring of the Cr⁶⁺ in environment. With the development of multi-parameter water quality monitoring system ( MS ), which can real-time, online, fast monitor the water quality. The MS utilization characteristics require the detection method of Cr⁶⁺ ion in water is simple and operated automatically, the reagent types and consumption used in the detection method must be less, at the same time the reagents must be stabile and longer longevity.The main objective of this study is to develop a detection method of Cr⁶⁺ in water for the MS. The national standard detection method of Cr⁶⁺ is beased on diphenylcarbazide (DPC) spectrophotometric determination,. The DPC standard method is simple and accurate, but the DPC chromogenic reagent is unstable, which lead to the reagent longevity is very short. MS mainly used for automatic, real-time monitoring the river water quality at wild stations. The unstable DPC chromogenic reagent can't meet MS requirements of the reagent service life. In this study, we modified the national standard DPC method. In the modified method, the DPC chromogenic reagent is very stable and the longevity has largely prolonged. The improved DPC chromogenic solution includes DPC, a solubility-enhancer A and a buffer B. The longevity of the improved DPC chromogenic reagent can reach 35 days when the reagent is avoided light stored in brown bottle at room temperature, which is significantly better than the DPC chromogenic reagent prepared according to the national standard method. The standard curve of the improved method is stabile in a week established with the improved chromogenic reagents, which obviously increase the accuracy of the detection results. At the same time, we optimize reaction system to reduce consumption of the reagents. The total reaction volume of the optimized reaction system is only 2.4 mL, which decrease greatly the reagent consumption than the national standard DPC reaction system. The optimized reaction system is suitable completely for the MS. The detection sensitivity of the modified DPC detection method is 0.7077, the linear range of detection sensitivity is 0 3.0 mg/L, and the detection limit is 0.003 mg/L, all the detection parameters are comparable with that of the standard level of the national standard DPC method. We detected the water samples of the Three Gorges Reservoir and the Jialing River with our modified DPC method. The relative standard deviation of the water samples at 5 times repeat experiments is less than 5% and the recovery reaches 95 105%, which fully reach the national detection standard of chromium ion. The reaction system can not only resist common ion disruption in water, but also resist the temperature effect at 5 40℃. The improved DPC detection method is convenient to detect hexavalent chromium ion, and facilitate the automatic detection of MS, which fully satisfied the requirements of MS. The method can be utilized broadly with MS for monitoring Cr⁶⁺ in environmental water at all parts of our country.