Determination of chromium by electrothermal atomic absorption spectrometry in waters using a forked platform and co-injection of Mg as chemical modifier

Two atomization techniques (wall and platform) for electrothermal atomic absorption spectrometry were compared for the determination of chromium in 0.5% (v/v) nitric acid. Magnesium nitrate alone and in conjunction with palladium nitrate as chemical modifier were compared. Different modifier injection modes, co-injection and pre-injection, were tested. Pyrolytic graphite forked (PGF) platforms and pyrolytic graphite-coated notched partition (PCN) tubes were used. The best analytical performance for chromium was obtained using PGF platforms with co-injection of 10 mug of Mg as Mg(NO3)(2) as chemical modifier. Maximum pyrolysis and atomization temperatures of 1900 and 2600 degreesC were found, respectively. The characteristic mass and limit of detection were 3.0 pg and 0.67 mug l(-1) for a 6 mul of Cr standard solution, using the auto-mix mode, respectively. The calibration graphs obtained were linear upto 450 pg of Cr. Analysis of NIST-1643d certified reference sample was performed and the result obtained was in good agreement with the certified value. Scanning electron micrographs of PGF platform and PCN tube surfaces revealed that the stabilization of chromium was probably due the formation of MgO. (C) 2001 Elsevier Science B.V. All rights reserved.