Salicylate, acetylsalicylate, benzalkonium, cholate, lidocaine were determined in some drugs and cocaine in illicit powders by means of new ISFETs based on ion selective polymeric membranes coated on the surface of the Si_3N_4 gate of a silica FET. The sensitive membranes consist of tetradodecylammonium salicylate (TDDAS), or benzyldimethylcetylammonium cholate (BDMCACh), or dodecyltri-methylammonium reineckate (DDTMAR), or cocaine reineckate (COC-R) respectively, as exchangers, polyvinyl chloride and a proper plasticizer. The linearity range of the sensor's is 5.0 centre dot 10~(-5) - 1.5 centre dot 10~(-2) mol/L (for salicylate), 7.0 centre dot 10~(-5) - 1.5 centre dot 10~(-2) mol/L (for acetylsalicylate), 2.5 centre dot 10~(-6) - 2.6 centre dot 10~(-3) mol/L (for benzalkonium), 1.2 centre dot 10~(-5) - 4.3 centre dot 10~(-3) mol/L (for deoxycholic acid), 1.0 centre dot 10~(-5) - 2.0 centre dot 10~(-3) mol/L (for chenodeoxycholic acid), 7.0 centre dot 10~(-6) - 1.0 centre dot 10~(-3) mol/L (for ursodeoxycholic acid), 2.5 centre dot 10~(-5) - 9.6 centre dot 10~(-3) mol/L (for lidocaine), 3.3 centre dot 10~(-6) - 2.1 centre dot 10~(-2) mol/L (for cocaine).
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