DETERMINATION OF THE THERMODYNAMIC STABILITY CONSTANT OF THE MAGNESIUM COMPLEX OF MALONIC-ACID BY USING AN ION-EXCHANGE INDUCTIVELY-COUPLEDPLASMA-ATOMIC EMISSION-SPECTROSCOPY METHOD

An ion-exchange column/inductively coupled plasma atomic emission spec troscopy method was employed to measure the thermodynamic stability co nstant of the 1:1 magnesium-malonate complex. The method involves pump ing buffered solutions containing magnesium and malonate ions through a microcolumn of strong-acid-type cation exchange resin until equilibr ium between the solution and resin phases is attained. After an air pu rge and water wash the sorbed magnesium ions, which are present in an amount related to the fi ee magnesium in solution, are eluted with nit ric acid and measured by inductively coupled plasma atomic emission sp ectroscopy. Although nonlinear calibration curves are obtained under t he nontrace ion-exchange conditions used, precise and accurate free ma gnesium concentrations are obtained. The method is straightforward and easy to use, and is applicable to a variety of systems that are not e asily measured by other methods.