Analysis of copper(ii) using the ascorbate/oxygen system - A valuable undergraduate resource

In deionised water, ascorbic acid (AH-), through oxidation by oxygen in the presence of copper(ii), was found to degrade with zero-order kinetics. The magnitude of the reaction rate varied directly with the copper(ii) concentration. At a higher pH (7.4), the same reaction was found to be pseudo-first order. Once again, the magnitude of the rate increased linearly with copper(ii) concentration at a micromolar level. Dissolved oxygen levels, in excess AH- and trace copper(ii), displayed similar kinetics under both conditions. Monitoring of either AH- levels or dissolved oxygen concentration was found to be a useful novel undergraduate practical laboratory for trace copper(ii) determination. Students can measure the kinetics for standards and their unknown copper solution and quantitate the unknown copper.