Multivariate optimization of a procedure for Cr and Co ultratrace determination in vegetal samples using GF AAS after cloud-point extraction

This work presents the development of a procedure for the determination of Cr and Co from vegetal samples using graphite-furnace atomic absorption spectrometry after cloud-point extraction. The procedure is based on extraction of metals from micellar media of octylphenoxypolythoxy-ethanol (Triton X-114) after complexing the metals with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol [5-Br-PADAP]. A Doehlert design was used to optimize the pyrolysis and atomization temperatures and pyrolysis time in the determination of analytes trapped in the micellar phase. Ascorbic acid and palladium were used as chemical modifiers, allowing a higher pyrolysis temperature without analyte losses. Enrichment factors of 26.2 and 41.0, along with detection limits (3 sigma(B)) of 23 and 12 ng L-1 for Cr and Co, respectively, were found. The precision expressed as relative standard deviation was 5.4 and 8.4% for metal concentrations of 0.5 mu g L-1 (n = 8) for Cr and Co, respectively. The accuracy was evaluated through the analysis of the certified reference material NIST 1515 (apple leaves). The procedure developed in this study was applied to the determination of Cr and Co concentrations in vegetal leaf samples.