Simultaneous determination of Cd, Pb, and Cu metal trace concentrations in water certified samples and soil extracts by means of Hg-electroplated-Ir microelectrode array based sensors

Abstract

Mercury-electroplated-iridium microelectrode array based sensors were successfully used for the simultaneous determination of Cd, Pb and Cu trace concentrations by means of square wave anodic stripping voltammetry (SWASV). These recently developed sensors consist of an array of (42×42) 6-μm-diameter iridium microdiscs onto which Hg microdrops are electroplated. The Ir microdisc arrays were achieved by using microfabrication processing techniques and a Hg charge of 15 mC was identified to be the optimum amount to be electroplated onto the 6-μm-diameter microdisc array. The microelectrode array based sensors were used to analyze both water certified samples covering a wide range of metal concentrations (from 1 to ∼1000 ppb) and soil extracts collected at different soil depths (from the surface to about 1 m depth in the Rouyn-Noranda region, Que., Canada). Different physico-chemical forms of the three metals were extracted from the soil samples using barium chloride, sodium pyrophosphate and oxalic acid/ammonium oxalate solvents. For the water samples, the measured Cd, Pb and Cu concentrations are found to be in a good agreement with the certified values (with an averaged recovery for the three elements of (103±15)%). On the other hand, all the Cd forms extracted from the soil are found to be ASV-electroactive since a satisfactory agreement was obtained between the concentrations measured by SWASV and those determined by means of graphite furnace atomic absorption spectrometry (GFAAS). While Pb and Cu concentration profiles in soil were found to be particularly dependent on the extractant used, Cd concentration profile exhibited the same trend for the three extractants. The differences in metal concentrations between extractants are discussed and the predominant physico-chemical metal forms are established as a function of the horizon in the soil profile. Finally, the developed SWASV sensors are shown to be successful to measure reliably metal concentrations as low as 50 ppt in soil extracts with a preconcentration time of only 10 min.