Electrochemical detection of arsenite with silver electrodes in inorganic electrolyte and natural system mixtures

Abstract

A detecção eletroquímica de arsenito com eletrodos de fio de prata (SWE) ou de disco de prata (SDE) foi realizada em soluções aquosas inorgânicas, as quais são similares àquelas encontradas em condições naturais. Voltametria cíclica (CV), voltametria de varredura linear (LSV) e voltametria de redissolução anódica (ASV) foram aplicadas. Os fatores investigados foram pH, natureza e concentração do eletrodo de suporte e tempo e voltagem de deposição para ASV. As mudanças de corrente e potencial de pico anódicos de As(III) em soluções padrão (por exemplo, 0,1 mol L-1 Na 2 SO 4 , NaNO 3 , HNO 3 and H 2 SO 4) foram avaliadas. Os meios neutro e básico de sais inorgânicos intensificaram a sensibilidade do eletrodo de prata mais que o meio ácido. Então, foi possível trabalhar em meio alcalino com sensibilidade aumentada para As(III) (limite de detecção de 90 ng L-1). A resposta analítica melhorada fez este sistema comparável a um eletrodo de nanoarranjo. Como o intervalo de uso destes eletrodos era largo, SWE (área de 6,47 mm 2) foi aplicado para monitorar a água de torneira usando 0,1 mol L-1 Na 2 SO 4 como eletrodo de suporte para detectar quantidades acima de 0,5 mg L-1 As(III). The electrochemical detection of arsenite with silver wire (SWE) or silver disc (SDE) electrodes was carried out in inorganic aqueous solutions, which are similar to those found under natural conditions. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and anodic stripping voltammetry (ASV) were applied. The investigated factors were pH, nature and concentration of supporting electrolyte and deposition time and voltage for ASV. The changes in the As(III) anodic peak current and potential in standard solutions (e.g., 0.1 mol L-1 Na 2 SO 4 , NaNO 3 , HNO 3 and H 2 SO 4) were evaluated. The neutral and basic media of inorganic salts were found to enhance the silver electrode sensitivity more than the acidic media. Thus, it was possible to work in alkaline medium with increased sensitivity for As(III) (limit of detection of 90 ng L-1). The improved analytical response made this system comparable to a nanoarray electrode. As the range of use of these electrodes was wide, SWE (area of 6.47 mm 2) was applied to monitor tap water using 0.1 mol L-1 Na 2 SO 4 as supporting electrolyte to successfully detect quantities above 0.5 mg L-1 As(III).

Advances in Electrochemical Detection Electrodes for As(III)

“…Several papers have reported on the silver-based electrochemical sensing of arsenic. Among them, María del C. Aguirre used a silver wire electrode (SWE) for the electrochemical detection of arsenite with a minimum detection limit of 0.09 ppb, indicating that SWE can be used for the detection of trace arsenic in alkaline and neutral media [ 111 ]. Baudelaire Matangouo Sonkoue generated silver nanocolloids by the chemical reduction of silver salts using citrate in aqueous solution and used a gold electrode modified with silver nanoparticles as the working electrode in linear sweep voltammetry for the detection of arsenic ions.…”

Recent advances in electrochemical detection of arsenic in drinking and ground waters

“…Based on such behavior, it is easy to obtain the lowest detectable As(III) concentration by applying a negative reduction voltage (À0.4 to À0.8 V vs. Ag/AgCl) with sufficient deposition times (300 to 2000 s) to electroplate As(0) on the Ag working electrode. 11 During the stripping step, the potential of the working electrode is reversed to a positive potential (>0.3 V) to oxidize As(0) to As(III), i.e., to strip off As(0) from the electrode's active surface. The anodic stripping step can be linear, pulse, staircase, or square wave.…”

“…Despite some controversial information about Ag as an electrode material, the Ag electrode has been reported to detect both high and low As(III) concentrations in a mixture with As(V). 11 For a sample with As(V) or a mixture of As(V) and As(III), the sample must be treated with a mixture of KI and ascorbic acid to enable the reduction of As(V) to As(III). 13 The Pt electrode is less sensitive for the detection of arsenic compared to the Au electrode.…”

“…For Ag electrodes, the arsenic stripping peak appears as a shoulder on the oxidation waves of the Ag electrode for arsenic determination via ASV. 11 However, when the electrolyte is HNO 3 instead of HCl, the oxidation of Ag that masks the arsenic stripping signal is shied to allow for a clear and detectable As(III) stripping signal. 26 With HNO 3 , a lower deposition potential is possible without hydrogen evolution and offers an LOD of 6.3 Â 10 À7 M (47.3 ppb) for As(III).…”

“…Thus, it is possible to work in alkaline medium (Na 2 SO 4 as supporting electrolyte) for the detection of As(III) with a LOD of 0.1 ppb by a Ag wire electrode. 11 This approach should be investigated further and the result must be corroborated with reference analytical techniques.…”