Adsorptive stripping voltammetry measurements of copper chelates of 3-methylxanthine and 7-methylxanthine

Controlled adsorptive accumulation of copper complexed with 3-methylxanthine (3MXan) and 7-methylxanthine (7MXan) on a hanging mercury drop electrode provides the basis for direct stripping measurement of these compounds at the subnanomolar concentration level. The height of the chelate peak, approximately 0.35 V more negative than the peak of the free compound, is shown to be proportional to the methylated xanthine (MXan) concentration. The adsorption and redox behaviour are indicated by ac and cyclic voltammetry. Experimental and instrumental parameters for quantitative analysis are optimized. A more sensitive peak is obtained in borate buffer. Under the optimum conditions the calibration curves are linear and the detection limits are given in absence and presence of Cu(II). The interferences of several organic compounds are evaluated.