Simultaneous Determination Of Cr (Ⅲ) And Cr (Ⅵ) By Spectrophotometry

The Cr(Ⅲ) and the Cr(Ⅵ) usually exist in simultaneously In the aqueous solution . The different chromium speciation will produce a different physiology function.The Cr(Ⅲ) is a kind indispensable little chemical element to human body , but the Cr(Ⅵ) compound just is a generally accepted carcinogen.At prerent,there are many directly spectrophotometry to multicomponent without any separation, but to the almost methords for determination of Cr(Ⅲ) and Cr(Ⅵ) are made on respectively after separation , or test out the content of Cr(Ⅲ) or Cr(Ⅵ) first then find out the total amount of chromium by oxidation or deoxidize, finally calculate one speciation by subtracting another speciation . In this paper , Dual-wavelength spectrophotometry and first derivative spectrophotometry have been used for the simultaneous determination of Cr(Ⅲ) and Cr(Ⅵ) and obtain a more satisfied result.The principle of equal absorption value point of Dual-wavelength spectrophotometry is used to determinate simultaneously Cr(Ⅲ) and Cr(Ⅵ) .The measuring wavelength is 352nm and the reference wavelength is 441nm for Cr(Ⅵ),Because the Cr(Ⅵ) has nointerference to the measurement of Cr(Ⅲ),Cr(Ⅲ) can be determine directly at the 542nm wavelength.When Cr(Ⅲ)/Cr(Ⅵ)=80-1/80(the mass ratio),the mass concentration ratio can reach 80 times,The linear range of Cr(Ⅲ) is 0～140 mg/L,equation of linear regression is A′=0.0037C-0.0003,linear regression coefficient r2=0.9999, and the detection limit is 0.007 mg·L-1.The linear range of Cr(Ⅵ) is 0～120mg/L,equation of linear regression is ?A′=0.02575C-0.00124,linear regression coefficient r2=0.9998 .,and the detection limit is 0.025 mg/L.The first derivative spectrophotometry is applied in simultaneous determination of Cr(Ⅲ) and Cr(Ⅵ).When interval factor is 10nm, first derivative value of mixed solution absorption can be get,and the concentration of Cr(Ⅵ) can be abttain by the first derivative value at 330nm wavelength,Because the Cr(Ⅵ) has no interference to the measurement of Cr(Ⅲ),Cr(Ⅲ) can be determine directly at the 542nm wavelength.When Cr(Ⅲ)/Cr(Ⅵ)=80-1/80(the mass ratio), the analytical maximumrelative error is 20 percent. The linear range of Cr(Ⅲ) is 0～140 mg/L,equation of linear regression is A′=0.0037C-0.0003,linear regression coefficient r~2=0.9999, and the detection limit is 0.007 mg·L-1 . The linear range of Cr(Ⅵ) is 0～120 mg/L, equation of linear regression is A′=0.00071C-0.00014,linear regression coefficient r2=0.99965,and the detection limit 0.005 mg/L.In this paper the ,Cr(Ⅲ) and Cr(Ⅵ) in true waste sample from Beijing Shuang- qiao electroplating plant were determined by using these two methods based on standard-adding method,angd got a satisfactory result.Thus,the two method established in this paper for the simultaneous determination of Cr(Ⅲ) and Cr(Ⅵ) in waste water are simple,accurate and dependable.