A sensitive electrode has been developed for the determination of arsenic As(III) ions by anodic stripping linear sweep voltammetry (ASLSV). The method shown in this work  for  the  electroanalytical  speciation  of  inorganic As(III) in water used a gold ultra-microelectrode array, consisted of 100 gold wires; each sized of 1 µm width and 1000 µm long. The sensor from gold band microelectrode arrays was made on a silicon wafer by the deposition and etching under angles (DEA) technique. The parameters of ASLSV, such as deposition potential (Edep) and time (tdep) and potential scan rate, were investigated. Different acidic solutions (HNO3, H2SO4, HClO4, H3PO4, HNO3/KCl, H2SO4/KCl and HClO4/KCl) with various concentrations were tested as a supporting electrolyte for arsenic analysis, from which the 0.1 M H3PO4 solution was chosen due to its medium acidity and being environmental friendly. Well defined voltammetric waves at Edep = -0.450 V (vs. Ag/AgCl reference electrode), tdep = 100 s and 1.000 V/s scan rate are found with peak currents proportional to the concentration of As(III) in the range of 10 to 100 ng.L-1. The limit of detection was 2 ng.L-1(signal-to-noise ratio = 3). These results well satisfy the requirements given by the World Health Organization (WHO). The repeatability, linearity and accuracy of the proposed method were evaluated. This method was applied for analysis of As(III) in natural water samples and the obtained results suggested that the fabricated gold chip would facilitate monitoring of As(III) in water. This research was part of the project ĐTĐL.2011-G/76, granted by the Ministry of Science and Technology (MOST) Vietnam. Keywords: anodic stripping voltammetry, arsenic, gold, ultra-microelectrode.

A gold ultra-microelectrode array has been developed for the determination of arsenic As(III) ions by linear sweep anodic stripping voltammetry (LSASV). The deposition potential (E dep ) and time (t dep ) and supporting electrolytes were investigated. The repeatability, linearity, accuracy of the proposed method and the effect of pH and interference ions were evaluated. It was found that As(III) can be determined by the proposed method using our developed gold ultra-microwire electrode at any pH including the pH values typical for natural waters. Well defined voltammetric waves at E dep = -0.450 V (vs. Ag/AgCl/3M KCl reference electrode), t dep = 100 s and 1.000 V.s -1 scan rate are obtained in 1M H 3 PO 4 supporting electrolyte. A good linear relationship between LSASV peak current and As(III) concentration is observed for the typical values in natural waters and in arsenic contaminated ones. The limit of detection was 2 ng.L -1 (signal-to-noise ratio = 3). The obtained results suggested that the fabricated gold chip would facilitate monitoring of As(III) in natural waters by linear sweep anodic stripping voltammetry.