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

Mercury-electroplated-iridium microelectrode array based sensors were succe ssfully used for the simultaneous determination of Cd, Pb and Cu trace conc entrations by means of square wave anodic stripping voltammetry (SWASV). Th ese recently developed sensors consist of an array of (42 x 42) 6-mum-diame ter iridium microdiscs onto which Hg microdrops are electroplated. The Ir m icrodisc arrays were achieved by using microfabrication processing techniqu es and a Hg charge of 15 mC was identified to be the optimum amount to be e lectroplated onto the 6-mum-diameter microdisc array. The microelectrode ar ray based sensors were used to analyze both water certified samples coverin g a wide range of metal concentrations (from 1 to similar to 1000 ppb) and soil extracts collected at different soil depths (from the surface to about Im depth in the Rouyn-Noranda region, Que., Canada). Different physico-che mical forms of the three metals were extracted from the soil samples using barium chloride, sodium pyrophosphate and oxalic acid/ammonium oxalate solv ents. 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 sinc e a satisfactory agreement was obtained between the concentrations measured by SWASV and those determined by means of graphite furnace atomic absorpti on spectrometry (GFAAS). While Pb and Cu concentration profiles in soil wer e found to be particularly dependent on the extractant used, Cd concentrati on profile exhibited the same trend for the three extractants. The differen ces in metal concentrations between extractants are discussed and the predo minant physico-chemical metal forms are established as a function of the ho rizon in the soil profile. Finally, the developed SWASV sensors are shown t o be successful to measure reliably metal concentrations as low as 50 ppt i n soil extracts with a preconcentration time of only 10 min. (C) 2001 Elsev ier Science B.V. All rights reserved.