TRACE ANALYSIS OF HEAVY METALS IN WATER BY CHROMATOGRAPHIC TECHNIQUES (ELECTROCATALYTIC)

The cation exchange separation and subsequent electrochemical or colorimetric detection of the resolved metal ions is a useful tool for the detection of transition metal ions. The metal ions were separated on a high capacity cation exchange column in the sodium form. The eluent used was a sodium tartrate-tartaric acid buffer. Experiments were conducted to determine the effect of tartaric acid concentration and soluble sodium salt concentration on the retention of the metal ions: copper, zinc, nickel, cobalt, iron, and manganese. Mathematical models were derived to explain the retention phenomena. It was shown that the logarithm of the adjusted retention time is proportional to the logarithm of tartaric acid concentration and inversely proportional to the logarithm of sodium concentration. Of the four detection methods investigated, secondary constant potential coulometric, direct reduction, electrocatalytic effect, and colorimetric detection, the electrocatalytic effect and colorimetric detection following a post-column reaction with PAR (4-(2-pyridylazo) resorcinol) were the most sensitive techniques. The electrocatalytic effect is based on the oxidation of the metal-tartrate complex and oxidation of the tartrate. The metal ions can then cycle through the reaction many times while present in the detector cell. This approach is limited in application to cobalt and manganese. The colorimetric detection following a post-column reaction with PAR is a very sensitive technique which can be applied to all of the metal ions under study.