Analytical Sciences, Talk
Direct voltammetric As(III) sensing in natural waters on a gel integrated renewable gold nanoparticle microelectrode
Romain Touilloux1, Marie-Louise Tercier-Waeber1, Eric Bakker1
1University of Geneva
Arsenic in the environment is of global concern because of the widespread chronic poisoning found in a number of countries and affecting large populations. Inorganic As(III) and As(V) species are the predominant forms in the water column, and a function of the local biogeochemical conditions, while organic forms are the main arsenic species in aquatic organisms. The As(III) species is 60 times as toxic as the pentavalent salt and several hundred times as toxic as methylated arsenicals. Robust and sensitive analytical tools capable of direct, continuous on-site As(III) sensing are therefore still of prime interest for the assessment of As health risks.

For this purpose, we have developed a microelectrode consisting of a renewable gold nanoparticle plated Ir-based microelectrode (AuNP-IrM) coated by a 350 to 650 µm thick agarose gel [1]. This layer minimizes fouling problems by hindering diffusion of colloids and macromolecules. Ir substrate pre-cleaning, AuNP deposition and renewal are controlled electrochemically. Square Wave Anodic Stripping Voltammetry (SWASV) has been used to characterize i) the flux of As(III) in the agarose gel as a function of the gel thickness and the temperature; and ii) the analytical performance of the sensor in synthetic and natural waters. The results show that the gel-integrated AuNP-IrM fulfills the requirements for direct measurements in freshwaters, i.e.: a mass transport of arsenite species in the gel controlled by pure diffusion ; a gel equilibration time varying with the gel thickness of the gel in accordingly to the theory ; a temperature effect on the SWASV As(III) signal intensities following a Arrhenius behavior and thus readily corrected using a factor defined in laboratory; a nanomolar detection limit at pH 8 ; and negligible Cu interference for Cu(II) to As(III) concentration ratios of ≤ 10. This sensing approach has been applied to environmental fresh water samples.
[1] Tercier-Waeber M. L. and Buffle J., Anal.Chem., 1996, 68, 3670-3678.