Sensitive cathodic stripping voltammetric procedures for trace determination of xanthine (I), 7-methylxanthine (II) and 1,7-dimethylxanthine (III) are reported. The methods are based on the accumulation of the copper(I) complexes of the compounds on the hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect to accumulation time, potential, concentration, pH and other variables. Linear calibration graphs were obtained over the range from 2.0 × 10−8 to 2.0 × 10−9 M; the limits of detection, with accumulation times of 4 min for I and III, and of 6 min for II, were calculated to be 5.0 × l0−10 1.0 × 10−9 and 5 × 10−10 M, respectively. Possible interferences by other purine derivatives were examined. The simultaneous determination of 1.7-dimethylxanthine (paraxanthine) and theophylline is possible by the proposed method.
Aminophylline is determined by cathodic stripping voltammetry (CSV) in BR buffer, pH 7.5 at a hanging mercury drop electrode. The detection limit was 3x108- M after 60 s accumulation at -0.60 V versus Ag/AgCl reference electrode. The linear range demonstrated up to 5x107-M using CSV. The interference caused by some purine derivatives, anions and some metal cations on the peak current was studied. The peak current is enhanced by theophylline, some methylguanines and copper (II) while it decreased or disappeared by citrate, chloride and Triton X-100 surfactant. The method has good sensitivity and its application to pharmaceutical samples is possible.