Fading spectrophotometric determination of zinc in salt with Zn~(2+)-phen-acid chrome blue K system

In ammonium chloride – ammonia buffer solution at pH 8.5,Zn2+ reacts with phen and acid chrome blue K(ACBK) to form a stable ion-association complex [Zn(phen)2]·,which leads to the fading of acid chrome blue K.Based on this fact,a new fading spectrophotometric method for the determination of zinc was proposed.The maximum fading wavelength located at 610 nm,with the apparent molar absorption coefficient of 2.41×104 L·mol-1·cm-1.The system's fading degree was linear with the concentration of Zn2+ in the range of 0~2.0 μg/mL.The detection limit was 20.3 μg/L.The method has been applied to the determination of zinc in health balance salt and fortified nutrient salt with zinc.The relative standard deviation was 0.66~0.74%(n = 5),and the average recovery was 99.3%~100.8%.