Electroanalytical sensors using lipophilic cyclodextrins
Lipophilic dialkylated-a-, β- and γ-cyclodextrin derivatives were used as selective ionophores for a series of clinically relevant ammonium ions, and as enantioselective ionophores for both a- and β-aryl ammonium ions. Sensitive and selective potentiometric detection of the local anaesthetics lidocaine and bupivacaine was achieved by using 2,3,6 trioctyl-β-cyclodextrin as the ionophore, leading to micromolar detection limits. Interference studies showed that the simulated clinical electrolyte background caused minimal interference whereas organic interferents of similar size and charge caused some perturbation of the electrode response at a concentration of 10 mmol dm(^-3). An electrode comprising a plasticized biocompatible membrane matrix, TECOFLEX, with 2,6 didodecyl-β-cyclodextrin was incorporated in a flow injection analysis system and the response to lidocaine studied in the presence of human serum. Human serum caused no adverse effects to the electrochemical response of the electrode. These electrodes are, therefore, very suitable for on-line detection of local anaesthetics. Potentiometric detection of tricyclic antidepressants using didodecyl-a-, β- and γ- cyclodextrins as the ionophore, gave micromolar detection limits. Interference from simulated clinical electiolyte background and selected organic interferents gave similar results to those discussed above. In order to lower the detection limit to sub-nanomolar levels modified amperometric electrodes were assembled by depositing a membrane comprising plasticised TECOFLEX, 2,3,6 triethyl-β-cyclodextrin and TKB on the working electrode of a screen printed electrode. Lipophilic 2,6 didodecyl-a- and β-cyclodextrins exhibited enantiomeric discrimination in the binding of propranolol, ephedrine, amphetamine and methamphetamine. These results were confirmed using potentiometric and NMR techniques.