The device has a fluid inlet; a filtering compartment, connected to the fluid inlet and accommodating a filtering matrix in presence of adsorption agents; a fluidic circuit connected downstream of the filtering compartment and including a discharge circuit and a loading circuit; a discharge chamber, connected downstream of the discharge circuit; a preparation outlet, connected downstream of the loading circuit; and suction pumps, connected to the fluidic circuit and configured so as to fluidically connect the filtering compartment alternatively to the discharge circuit or to the loading circuit.