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

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 electrothertnal 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)9 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 NaBH4 in 0.10 mol l(-1) of NaOH) and 1.0 ml of reference or sample solution in 0.25 mol l(-1) of HNO3 were carried to the gasliquid 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, 38). The reliability of the entire procedure was confirmed by addition and recovery tests and cold vapor atomic absorption spectrometry. (C) 2002 Elsevier Science B.V. All rights reserved.