Preparation of the thin film Membrane filter papers were Millipore of 0.45 m pore size. Dif-ferent amounts (5, 10, 15, 20, 25 and 30 mg) of the loaded ALIQUAT336-MWCNTs containing the preconcentrated As(V) were used toprepare the films in order to determine its critical thickness. Thefiltrations were performed in a filtration apparatus equipped witha vacuum pump (De Vito et al., 2001).A series of aqueous properly diluted As(V) solutions were pre-concentrated. This was done on the ALIQUAT 336-MWCNTs by