Complexation of Hg(II) by humic acid studied by square wave stripping voltammetry at screen-printed gold electrodes

Abstract

This paper reports the development of a sequential injection (SI) method to study the complexation of Hg(II) by humic acid (HA) using square wave anodic stripping voltammetry at a screen-printed gold electrode (SPGE). The SI system injected samples (in 0.020 mol L(-1) NaNO(3) and pH 6.0) to the flow cell during the deposition step and exchanged the medium to 0.050 mol L(-1) HCl to perform the stripping step under stopped flow conditions. For sample volume=750 μL, flow rate=15 μL s(-1) (deposition step), and square wave frequency=100 Hz, the detection limit was 20 nmol L(-1) and the sampling throughput was 17 analyses per hour. Complexation of Hg(II) was studied using a 25.0 mg L(-1) suspension of HA (72.5 μmol L(-1) of ionizable sites), and total Hg(II) concentrations from 1 to 20 μmol L(-1). The diffusion coefficient of the complex was (1.3±0.2)×10(-7) cm(2) s(-1). A complexing capacity of 537 μmol g(-1) was found. The log of the differential stability constant (logK(DEF)) decreased from 7.0 to 5.3 as the log of the degree of site occupation (logθ) increased from -1.6 to -0.5. The values of logK(DEF) were consistent with complexation of Hg(II) by carboxylic and phenolic groups.

Screen-Printed Electrodes Modified with “Green” Metals for Electrochemical Stripping Analysis of Toxic Elements

“…Several authors have utilized SPEs with Au-loaded carbon inks for the determination of Hg [ 43 ] and Pb [ 30 , 44 ]. These devices are ready to use since they do not require an Au plating step.…”

Especiação Dinâmica De Metais Traço Em Ambiente Aquático Usando Cronopotenciometria De Redissolução Anódica

“…108,[112][113][114][115] Sensores impressos de ouro, por exemplo, foram usados para investigar as interações dinâmi-cas de Hg(II) com ácidos húmicos e suspensões de microalgas. 110,111 Assim, estudos recentes têm demosntrado que metais como ouro e bismuto apresentam propriedades eletroquímicas que permitem seu uso em especiação dinâmica, sendo considerados "ambientalmente amigáveis" por serem menos tóxicos e terem enorme potencial para viabilizar a realização de estudos on site. [109][110][111]116 …”

“…110,111 Assim, estudos recentes têm demosntrado que metais como ouro e bismuto apresentam propriedades eletroquímicas que permitem seu uso em especiação dinâmica, sendo considerados "ambientalmente amigáveis" por serem menos tóxicos e terem enorme potencial para viabilizar a realização de estudos on site. [109][110][111]116 …”

The Utilization of Nitrogen Gas as a Carrier Gas in the Determination of Hg Ions Using Cold Vapor-Atomic Absorption Spectrophotometer (CV-AAS)

“…Several methods for the determination of Hg have been reported in the literature, such as potentiometric titration using iodide ion-selective electrodes and anodic stripping voltammetry [5], and some spectrometric techniques, such as cold vapor atomic absorption spectrometry (CV-AAS) [6][7], electrothermal atomic absorption spectrometry (ETAAS) [8], atomic fluorescence spectrometry (AFS) [9], inductively coupled plasma mass spectrometry (ICP-MS) [10] and electrothermal vaporization coupled to ICP-MS (ETV-ICP-MS) [11] were already employed for total Hg determination in the samples.…”