Optimization of focused microwave-assisted extraction of DDT and derivatives from soil samples

Optimization of focused microwave (FMW)-assisted extraction of 4,4'-DDE, 4,4'-DDD, and 4,4'-DDT from soil samples was carried out using central composite designs. All the extracts were analyzed with GC/MS and some of them also with GC/AED using columns of different polarities for each of the techniques, The extraction of the analytes was carried out in two ways: with acetic acid as microwave radiation absorbent solvent and n-decane to concentrate the analytes and with reagent water and iso-octane as solvents. In the first case, the influence of the extraction temperature, the extraction time, and the addition of sodium chloride were studied and the optimum conditions for the extraction of 1 g of soil with 5 mL of acetic acid and 2 mL of n-decane were 1.30 mol L-1 sodium chloride at 98 degreesC for 9.3 min. In the second case, the temperature was kept constant (94 degreesC) and the influence of the concentration of sodium chloride and the extraction time were studied. The optimum conditions were 5 mL of a 2.0 mol L-1 sodium chloride together with 2 mL of iso-octane for 15 min, The recoveries obtained by water-FMW extraction were significantly lower than those obtained by the acetic acid-FMW procedure. These last recoveries were in good agreement with those obtained by closed microwave assisted-extraction with acetone-n-hexane as solvent.