Faradaic and Capacitive Current Estimation by DPV-ATLD

Abstract

In this work we for the first time proposed an approach based on ATLD which enabled exploration of the faradaic and double-layer charging current components in voltammetric experiments in the presence of surface-active substances. For simulated data ability to successful decomposition of the signals was confirmed and theoretic shape of two original components was restored. Next the proposed approach was applied in determination of Pb(II) in the presence of the increasing CTAB concentration. Considering calibration set of Pb(II), sampled with frequency of minimum 1 kHz, it was proved that total current may be effectively separated into two components. Capacitive current in the case without CTAB addition was ca. 15% higher in comparison with the case when 2 or 4 mgL−1 of CTAB was present, but decreased faster, and after 20 ms it reached the same value. Faradaic current decreased significantly with CTAB addition but the linear relation with depolarizer concentration was preserved. The calibration models were defined omitting the separated capacitive current component, what improved analytical parameters of the method. Using sampling period of 3 to 6 ms from the potential change, the sensitivity increased 2.7-3 times (depending on the CTAB concentration) in comparison with the typical interpretation, detection limit was also lower and reached 0.2–0.4 μgL−1 of Pb(II). For each concentration of CTAB the correlation coefficient r in lead determination was greater than 0.9970, while the repeatability expressed by the coefficient of variability was lower than 3%.