Direct speciation analysis of Cr(VI) by electrothermal atomic absorption spectrometry, based on the volatilization of Cr(III) thenoyltrifluoracetonate from the graphite furnace

A new method for the direct determination of Cr(VI) by electrothermal atomic absorption spectrometry has been developed. The formation of a volatile complex between Cr(III) and thenoyltrifluoracetonate was used to separate both species. The optimum conditions for complex formation were: pH range 5-6 (using HAc/NaAc as a buffer solution), sonication time of 5 s at 40 degreesC with a reaction time of 3 h and 30 min before measurement. At temperatures above 700 degreesC the complex formed was completely volatilized, making Cr(VI) determination possible, independent from Cr(III). The optimum temperature program for Cr(VI) determination was 1600 and 2400 degreesC for pyrolysis and atomization, respectively. Better separation of the species was obtained when 5 mg 1(-1) of palladium was added as a modifier. The developed method was precise (with R.S.D. < 10%), with a detection limit of 0.7 mug l(-1) Cr. CRM 544 (lyophilized chromium) was used to demonstrate the accuracy of the method. (C) 2002 Elsevier Science B.V. All rights reserved.