Determinação de metais em matrizes oleosas por HR-CS AAS após extração induzida por quebra de emulsão

Abstract

Three methods based on extraction induced by emulsion breaking were developed for the extraction and determination of metals in asphalt and oilseeds by high-resolution continuum source atomic absorption spectrometry with graphite furnace atomization. The first method reports the extraction of Cr, Cu and Mn from asphalt through the formation and breaking of oil-in-water (O/W) emulsions. Under optimized conditions, the sample (0.05 g), diluted in toluene (1.5 mL) and mineral oil (0.5 mL), was mixed with 5 mL of the extractant solution (Triton X-100 3% w/v and HNO3 15% v/v). Breaking occurred by heating at 90°C (20 min). The extraction efficiency ranged from 88.6 for Cu to 104% for Mn. Mono-elemental determination was performed on the primary lines of the three analytes. The limits of detection (LOD) were 0.02, 0.01 and 7.11 μg g-1 for Cr, Cu and Mn, respectively. Precision, expressed as relative standard deviation (RSD), ranged from 1.0 for Cu to 9.1% for Cr. The performance of the proposed method was compared to procedures reported in the literature, including microwaveassisted acid digestion (MW-AD), ultrasound-assisted acid extraction (USE), emulsification (E), and direct dilution (DD). The methods with the best performance parameters for Cu were EIEB, MW-AD, USE and E. For Cr and Mn, the best results were obtained by EIEB, MW-AD and DD. The second method reports the extraction of Co, Fe and Ni from asphalt through the formation and breaking of water-in-oil (W/O) emulsions. Under optimized conditions, the sample (0.08 g), diluted in toluene (1.5 mL) and mineral oil (3.5 mL), was mixed with 2 mL of the extractant solution (40% HNO3 v/v and Triton-X -100 40% v/v). Breaking occurred by heating at 90°C (15 min). Extraction efficiency ranged from 101 for Co to 104% for Ni. Simultaneous determination was performed on the secondary lines of Co (352.685 nm), Fe (352.604 nm) and Ni (352.454 nm). LODs were 0.025, 0.450 and 0.225 ng g-1 for Co, Fe and Ni, respectively. RSD ranged from 0.1 for Ni to 7.2% for Co. The third method describes the extraction of Ba, Co, Fe and Ni from oilseeds through the formation and breaking of solid-oil-water (S/O/W) emulsions. Under optimized conditions, the sample (0.8 g) was mixed with 4 mL of the extractant solution (20% v/v HNO3 and 15% w/v Triton-X- 100). Breaking occurred by heating at 90 °C (4 min) followed by centrifugation. The extraction efficiency ranged from 94.9 for Ba to 110% for Fe. Simultaneous determination was performed at secondary lines of Ba (352.497 nm), Co, Fe and Ni. The LODs were 19.95, 0.012, 0.474 and 0.011 μg g-1 for Ba, Co, Fe and Ni, respectively. RSD ranged from 0.4 for Ni to 8.0% for Co. The three proposed methods are simple, fast and low cost. Thus, they can be considered excellent alternatives to conventional sample preparation methods.