Differential Kinetic method for simultaneous determination of manganese and zinc based on a ligand substitution reaction

　A spectrophotometric kinetic method for simultaneous determination of manganese and zinc has been described. The method is based on the differential reaction rate of the ligand substitution reactions between 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino) phenol (PAPS) chelates of these metal ions and ethyleneglycolbis (2-aminoethylether)-N,N,N’,N’-tetraacetic acid (EGTA). Manganese and zinc are determined with a graphical extrapolation by decrease in the absorbance of the characteristic wavelength at 560 nm at pH 10.0 and 25.0℃. The 10^-9 M levels of manganese and zinc can be determined simultaneously without prior concentration process. Cadmium, copper, mercury and lead were masked by adding dithiocarboxy-sarcocine. Compornents of slow rate of reaction, such as cobalt, iron and nickel do not intefere the determination. The proposed method was applied to determine manganese and zinc at several ppb(μg/kg) levels in a freshly precipitated snow sample.