The influence of Eacc on the recorded stripping peaks of Gua and Ade was examined over the potential range of −0.4 to +0.2 V. The results revealed that the peak height for both compounds slightly decreased by changing the accumulation potential from −0.4 to 0.0 V. In contrast, the peak height rapidly decreased when Eacc was changed to more positive values that can be explained by poorer adsorptive ability of these substances at a positively charged surface of ACSE. However, in case of the pre-concentration of analytes at an applied potential the background current also increased. The best results in terms of the stripping peak height-to-background ratio were obtained for adsorptive accumulation of Gua and Ade under open-circuit condition.
It is well known that the accumulation efficiency is the most critical parameter, which controls the ultimate detection sensitivity. In AdSVA methodology, it depends on the tacc and the mass-transfer during accumulation. The adsorptive accumulation of Gua and Ade on the activated CSE under open circuit conditions was evaluated by varying tacc from 0 to 600 s. As it can be seen from the stripping voltammograms, shown in Fig. 5, the peak heights for both compounds increased greatly as tacc increased up to 240 s. For tacc greater than 240 s, it tended to be almost stable. Considering both sensitivity and work efficiency, tacc of (60–240) s was used in further experiments. The peak currents (after background correction) of Gua and Ade at tacc 120 s were about 1.5 and 1.9 times of that without accumulation, respectively.