Catalytic Adsorptive Stripping Chronopotentiometric Determination of Hexavalent Chromium at a Silver Amalgam Film Electrode of Prolonged Application

Abstract

The paper reports on the application of stripping chronopotentiometry for the determination of chromium(VI) at a silver-based amalgam film electrode. It is the first attempt to apply such a detection system for the speciation of chromium. The procedure utilized catalytic reduction of nitrate ions induced by the instantaneous chromium(III)-DTPA complex, accumulated at the electrode surface. The chronopotentiometric step is realized in the constant current mode. Several key parameters, such as the deposition potential, deposition time, nitrate concentration and stripping current were optimized. The detection limit obtained for 15 s of accumulation time was estimated at 0.025 mg/L. The repeatability of the signal was 6.1 %.Keywords: Silver-based amalgam film electrode, Catalytic adsorptive stripping chronopotentiometry, Chromium(VI), River water DOI: 10.1002/elan.201100237 Stripping chronopotentiometric analysis (SCP) is a valuable alternative to stripping voltammetry; it is, however, far less popular and utilized in analytical practice. The SCP technique, as in the case of stripping voltammetry, involves two steps, i.e. potentiostatic pre-concentration followed by stripping accompanied by oxidation, reduction or desorption of the pre-concentrated analyte [1]. During the latter step, two different stripping mechanisms can be exploited: chemical oxidation/reduction caused by the oxidant/reductant present in the solution, or oxidation/reduction by means of constant current (CC-SCP). The application of the constant-current approach ensures more standardized conditions and better control of the stripping process. During the course of the second step, the potential of the working electrode varies with time, and the potential-time curve is usually recorded and then transformed into the dt/dE vs. E form. Since it has been proved empirically that SCP is less sensitive to the presence of relatively high concentrations of organic matter, this technique found its application as an alternative to non-electrochemical techniques (e.g. GFAAS, ICP-OES) in the determination of total metal concentration in food or beverage samples [2,3]. Depending on the working electrode applied, the mechanism of analyte accumulation may vary. The utilization of electrodes based on mercury enables the accumulation of some heavy metals via their amalgam formation [4] in the anodic version of SCP.The second approach utilizes the deposition of analyte in the form of complexes adsorbed on the electrode surface. Usually, these complexes are subsequently reduced with the negative stripping current.In SCP various types of electrodes have been used, such as: glassy carbon electrodes [5], gold electrode [6,7], carbon fiber [8], carbon paste electrode [9, 10], bismuth or antimony plated film electrodes [11][12][13] and screenprinted carbon-ink electrodes [14]. The electrodes used most frequently are the mercury-based electrodes [15][16][17][18]. Their excellent analytical performance and their advantages are obvious. However, liquid mercury electro...

Voltammetric behavior of erythromycin ethylsuccinate at a renewable silver-amalgam film electrode and its determination in urine and in a pharmaceutical preparation

“…Moreover, the renewal of the amalgam-film-based sensor surface usually provides good reproducibility and repeatability of the analytical signal [40]. It has successfully been used in the determination of trace levels of some metals, such as zinc [35,43], copper [35], vanadium (V) [37], manganese (II) [38], molybdenum (VI) [39], uranium (VI) [40], chromium (VI) [41,42], cobalt, nickel [45], lead, cadmium [43], gallium [36] and palladium (II) [44]. In addition, this electrode is suitable for the determination of different organic compounds [46-52, 56, 57] with characteristic electroactive groups in their structures, such as nitro compounds [46][47][48], guanidine [49,50], quinone [57], some vitamins [56], pharmaceuticals like moroxydine [49] and doxorubicin [57], pesticides, e.g.…”

Renewable silver amalgam film electrodes in electrochemical stripping analysis—a review

“…Replacing this mercury film electrode with the Hg(Ag)FE-c can simplify and facilitate CC-SCP analysis under on-site conditions. So far, this approach has been presented in two papers, in which the first attempts to apply the Hg(Ag)FE-c for the determination of several heavy metals by means of constant current anodic stripping chronopotentiometry (CC-ASCP) [70] and of Cr(VI) via constant current catalytic adsorptive stripping (CC-CAdSCP) [71] have been undertaken.…”

Electrochemical stripping analysis

“…AdSV and CAdSV methods have found wide applications for chromium speciation in various environmental samples 145,150 . The past two decades of research have seen the application of not just mercury electrodes but also environmentally friendly sensors such as silver amalgam [173][174][175] and various types of bismuth film electrodes [176][177][178][179][180] . A CAdSV procedure to monitor chromium traces using a submersible electrochemical probe and dialysis membrane that prevents electrode fouling has also been described 156 .…”