Xylenol orange spectrophotometric determination of trace of Co~(2+) in water

Color development reaction between xylenol orange(XO) and Co2+ was systematically studied.Based upon this reaction,a xylenol orange spectrophotometric method was established for determining trace of Co2+ in water.Impact of various conditions on the measurement result,such as acidity of the solution,amount of color developing agent used,time for color development, temperature,addition of surfactant,co-existing component and interferential ion,were discussed.Experimental results showed that,Co2+ reacts rapidly with XO in acetic acid–sodium acetate buffer medium at pH 5.5 and forms a purple red complex with maximum absorption wavelength of 578 nm.Co2+ mass concentration,within the range of 0~1.8 μg/mL,has good linearity vs the light absorbance of the complex.Regression equation is found to be A=1.879×10-2ρ–2.597×10-2.The correlation coefficient ris equal to 0.999 46.The apparent molar absorptivity is found to be 2.62×104 L·mol-1·cm-1,and the detection limit is 2 μg/L.This method has been used for determination of Co2+ in city water with recovery achieves 99.0%～101.0%.