the silica concentrator is a polycationic organic polymer, preferably a long chain polyamine, preferably selected from the group consisting of polycation poly(diallyldimethylammonium) chloride (PDADMAC); spermine; cholesteryl spermine; spermidine; spermidine tryhydrochloride; spermidine phosphate hexahydrate; L-arginyl-3,4-spermidine; 1 -4-butanediamine N-(3-aminopropyl)- monohydrochloride; putrescine (1 ,4-diamino-butane); 1 ,3-diamino-propane; 1 ,7- diamino-heptane; 1 ,8-diamino-octane; poly(allylamine) hydrochloride; poly(ethyleneimine); poly(N-methylethyleneimine); poly(N-vinyl-2-pyrrolidone); poly(2- (dimethyl-amino)ethyl methacrylate; chitosan; poly(vinylamine) hydrochloride; poly(propyleneimine); poly(N-methylpropyleneimine); poly(acrylamide-co- diallyldimethylammonium) chloride; poly-L-lysine; poly-L-arginine andpoly-L-histidine or a mixture thereof