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 °C with a reaction time of 3 h and 30 min before measurement. At temperatures above 700 °C 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 °C for pyrolysis and atomization, respectively. Better separation of the species was obtained when 5 mg l−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 μg l−1 Cr. CRM 544 (lyophilized chromium) was used to demonstrate the accuracy of the method.