Supercritical fluid extraction of organochlorines from fish muscle with different sample preparation

Supercritical carbon dioxide was used to extract PCBs, p,p′-DDE, p,p′-DDD, p,p′-DDT and dieldrin from fillets of black scabbardfish (Aphanopus carbo). Using standards, the optimal extraction conditions of pressure and temperature were determined using the statistical method of central composite surface design. The studied temperatures ranged from 309 to 337 K and pressure from 10 to 24 MPa. It was observed that temperature do not affect significantly the extraction and, on the contrary, a significant effect was recorded for pressure. The best extraction efficiencies were obtained at pressures near 14 MPa, for all the studied compounds. To study the matrix effect on the yields, three types of raw materials were selected: fresh fillet, fresh fillet with anhydrous sodium sulphate and freeze-dried fillet. It was observed that supercritical carbon dioxide can extract efficiently the organochlorine compounds from freeze-dried fillets, but very low recoveries were obtained from fresh fillets. The pressure effect on extraction was studied for the freeze-dried samples. Three pressures were tested: 18, 22 and 26 MPa, maintaining the temperature at 328 K. Analysing the initial extraction velocities it was observed that 22 MPa was the optimal extraction pressure. The concentration of organochlorine compounds obtained by supercritical fluid extraction was, in some cases, higher than those obtained by Soxhlet extraction, using n-hexane.