Rapid spectrophotometric determination of a micro amount of silver utilizing substitution reaction between tetracyanonickelate and silver

Abstract

Silver ion reacts with tetracyanonickelate to form dicyanoargentate. The substitution reaction proceeds quantitatively by the following equation.
Ni(CN)₄^2-+2Ag⁺→Ni²⁺+2Ag(CN)₂^-
The stoichiometrically released nickel ion then reacts with 4 (2-pyridylazo) resorcinol (PAR) forming Ni-PAR chelate which shows absorption maximum at 496 mμ. A molar extinction coefficient of Ni-PAR chelate is 7.30×10⁴. The micro amount of silver in concentration of 5.00×10^-6 1.95×10^-5mol/l can be indirectly determined by measurement of the absorbance at 496 mμ.