Development of a slurry-extraction procedure for direct determination of cobalt by electrothermal atomic absorption spectrometry in complex environmental samples Original Research Article

A new procedure for Co determination in a complex matrix (coal fly ash) by slurry extraction-electrothermal atomic absorption spectrometry (ETAAS) is presented. Fractional experimental designs were applied to find the most important variables affecting Co extraction. Two liquid media (HCl + HNO3 and HF) and three agitation modes (ultrasonic probe, ultrasonic bath and manual shaking) were assayed. HF revealed as the most suitable medium for Co extraction, being its concentration and time of contact the most significant variables. Quantitative extraction was obtained after their optimisation (16%, v/v HF; 5 min), with good accuracy (coal fly ash SRM 1633a and SRM 1633b) and precision (R.S.D. < 11.5%). The limit of detection of the method was 0.02 μg g−1 (100 mg mL−1 slurry), and the characteristic mass was 15 ± 1 pg. The ‘slurry-extraction procedure’ established is simple, fast, cheap and was also validated for soil and sediment analysis. As far as we know, a slurry-extraction procedure has not yet been applied to quantify cobalt by ETAAS in such matrices. Moreover, nine coal fly ashes, 12 sediments and 18 soils were analysed by the proposed method and also by a direct slurry sampling-ETAAS procedure in order to compare their performance. In general, the HF-extraction slurry procedure revealed superior.