An electrochemical flow-cell for permanent modification of graphite tube with palladium for mercury determination by electrothermal atomic absorption spectrometry

Abstract

An electrochemical procedure for palladium deposition on the inner surface of pyrolytic graphite-coated tubes for permanent chemical modification and a cold vapor generation system for the pre-concentration and determination of mercury trace levels in rain, potable, and non-potable water and lake sediment by electrothermal atomic absorption spectrometry is proposed. A tubular electrochemical flow-cell was assembled on the original geometry of the graphite tube, which operated as the working electrode. A stainless steel tube, positioned downstream from the working electrode, was used as the auxiliary electrode. The applied potential was measured against a micro Ag/AgCl (sat) reference electrode inserted in the auxiliary electrode. Palladium solution in acetate buffer (100 mmol l −1, pH=4.8), flowing at 0.5 ml min −1 for 60 min was used to perform the electrodeposition. A homemade cold vapor generation system composed of a peristaltic pump, an injector–commutator, a flow meter and a disposable polyethylene gas–liquid separator flask (approx. 4.0 ml volume) were used. Volumes of 1.0 ml of reagent (2.0% w/v NaBH 4 in 0.10 mol l −1 of NaOH) and 1.0 ml of reference or sample solution in 0.25 mol l −1 of HNO 3 were carried to the gas–liquid separator using the peristaltic pump. The mercury vapor was carried out to the modified graphite tube by argon flow (200 ml min −1), and pre-concentrated for 120 s. The characteristic mass for 1.0 ml of reference solution was 26 pg (R.S.D.=0.12%, n=5). The detection limit obtained was 93 pg ( n=20, 3δ). The reliability of the entire procedure was confirmed by addition and recovery tests and cold vapor atomic absorption spectrometry.