Elsevier

Electrochimica Acta

Volume 178, 1 October 2015, Pages 665-672
Electrochimica Acta

New voltammetric sensor based on the renewable bismuth bulk annular band electrode and its application for the determination of palladium(II)

https://doi.org/10.1016/j.electacta.2015.08.047Get rights and content

Abstract

A study of a new type of voltammetric sensor based on the renewable bismuth bulk annular band working electrode (RBiABE) for palladium(II) detection via differential pulse adsorptive stripping voltammetry (DP AdSV) after complexation with dimethylglyoxime (DMG) in an acetate buffer (pH 4.1) and without deaeration is reported. The experimental variables (composition of the supporting electrolyte, pH, potential and time of pre-concentration and DP parameters) as well as possible interferences were investigated and optimized. The peak current was proportional to the concentration of Pd(II) over the range from 9.4 × 10−8 to 9.4 × 10−6 mol L−1 (R = 0.9993) and from 9.4 × 10−9 to 9.4 × 10−8 mol L−1 (R = 0.9995) for accumulation times of 10 s and 40 s, respectively. For 40 s of accumulation time, the limit of detection was 8.9 × 10−10 mol L−1 (0.12 μg L−1) (at S/N = 3), with a sensitivity of 0.84 nA/nM. The relative standard deviation for 9.4 × 10−8 mol L−1 Pd(II) was 5.1% (n=5). Finally, the proposed method was successfully applied and validated by studying the recovery of Pd(II) from spiked tap and river water samples.

Introduction

In the last decade there has been an increase in the consumption of palladium in many industries. About half of the annual production of this metal is used in the car industry for the manufacture of catalytic converters [1]. The remainder is used in other sciences and technologies, such as metallurgy, electronics, dentistry, medicine or jewelry. Palladium bimetallic catalysts are involved in numerous processes of the selective hydrogenation of unsaturated hydrocarbons, e.g. in the selective hydrogenation of alkynes to alkenes and vice versa [2]. Numerous applications of palladium and its harmful effects on human health have become the main reasons for the need to monitor its concentration in the environment.

In recent years, relatively little work on the determination of platinum group metals (PGMs) including palladium has been reported in the literature. The main research in this field has concerned the determination of these metals in soil samples and air particulate matter, and, less frequently, in surface water and food. In most cases, the researchers used spectroscopic [3], [4], [5] and voltammetric techniques with the hanging mercury drop electrode (HMDE) [6], [7], amalgam film electrode (Hg(Ag)FE) [8], glassy carbon bismuth film electrode (GC/BiFE) [9] or screen-printed carbon electrode coated with a bismuth film (SPCE/BiF) [10] as working electrodes. The most frequently cited works used mercury electrodes for palladium determination. Their application in stripping voltammetric methods ensures high sensitivity, a low limit of detection, and very good reproducibility of the results. However, the issues related to the toxicity and disposal of mercury make measuring devices that contain it unsuitable for routine analysis [11].

As an alternative to mercury electrodes, the environmentally friendly bismuth electrode can be used. A bismuth film electrode (BiFE) was proposed for the first time in 2000 by Wang et al. [12]. Due to its less toxic character, wide operational potential window, and improved performance in the presence of dissolved oxygen, bismuth has been accepted as an efficient replacement for mercury. In most previous designs, the BiFE has been prepared by electrochemically depositing thin films from solutions containing Bi3+ ions on the substrate (carbon, metals) surface [13], [14], [15]. In addition to its many advantages, it also has several drawbacks, including a comparatively low limit of detection, the necessity of purifying and polishing the substrate surface, or the durability of the plated film. Therefore, in addition to BiFEs, the following types of modified electrodes have also been used: screen-printed carbon electrodes with a bismuth film [10], bismuth-modified carbon nanotubes, bismuth single-crystal plane electrodes, and bismuth-modified carbon paste electrodes [16], [17], [18].

Of the many different reports, only a few studies have concerned the application of bismuth bulk electrodes (BiBEs) in stripping voltammetry (SV). This type of electrodes can, however, offer several advantages, such as: –the minimization of the amount of generated waste (a solution of bismuth salt is not needed to prepare the film), ease of its use and fabrication, cost-efficiency and stability (under potential control). Until now, the application of BiBEs in trace metal analysis has mainly focused on the determination of Cd, Pb and Zn [19], [20], and rarely on the determination other metals such as Ni and Co [21], [22] or the speciation analysis of Cr(III) and Cr(VI) [14]. Several organic compounds have also been analyzed using BiBEs [23], [24].

In this work, the fabrication of a new voltammetric sensor with the renewable bismuth bulk annular band working electrode (RBiABE) and its application in adsorptive stripping voltammetric (AdSV) determination of Pd(II) are presented. The construction of this sensor is similar to those of other sensors with the renovated metal and ceramic ring electrode described in our previous reports [22], [25], [26], [27]. The presented concept entails fast (several seconds long) electrochemical regeneration of the Bi electrode in the electrolyte solution filling the sensor body before each measurement. The optimal conditions for the determination of Pd(II) in the form of the DMG complex in an acetate buffer at the RBiABE were established. The recovery of the method was evaluated using natural water samples from the Rudawa river (Kraków, Poland) spiked with palladium(II). Potential interferences from coexisting ions, organic matter and surface-active substances were determined using commercially available humic acid and Triton X-100.

Section snippets

Chemicals and glassware

All chemicals were of analytical reagent grade and used as received. All aqueous solutions were freshly prepared with fourfold distilled water (two last stages from quartz). Atomic absorption standard solutions of palladium(II) were purchased from Merck (Certipur®, 1000 mg L−1) and diluted prior to use. 0.5 mol L−1 acetate buffer (pH 4.1) was prepared by mixing the appropriate amounts of 96% acetic acid and sodium acetate (both Suprapur®, Merck). A 0.01 mol L−1 dimethylglyoxime (DMG, Sigma-Aldrich)

Cleaning procedure

In the case of solid-state electrodes (SSEs), continuous renovation of their surface is indispensable for ensuring reliable results of measurements. This process restricts the impact of surfactant adsorption on the surface of the electrode as well as the physical changes (morphology – roughness) and chemical reactions (such as oxidation) that occur on this surface. These phenomena may lead to a reduced signal, peak broadening, or even shifts in the peak potential. Renewable metal annular band

Conclusions

In this work, a new electrochemical sensor based on the renewable bismuth bulk annular band working electrode (RBiABE) is applied for the first time to determine palladium(II) by means of differential pulse adsorptive stripping voltammetry (DP AdSV) after complexation with dimethylglyoxime (DMG) in a non-deaerated acetate buffer (pH 4.1). Under optimized conditions, the detection limits of 5.2 × 10−9 mol L−1 (0.70 μg L−1) and 8.9 × 10−10 mol L−1 (0.12 μg L−1) were obtained for accumulation times of 10 and

Acknowledgements

This work was supported by the Polish National Science Centre (Project No. DEC-2011/03/B/ST5/02713).

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