Determination of l-carnitine using enantioselective, potentiometric membrane electrodes based on macrocyclic antibiotics

In order to determine the enantiopurity of l-carnitine three enantioselective, potentiometric membrane electrodes were proposed for the assay of l-carnitine. The electrodes were designed using macrocyclic glycopeptide antibiotics—vancomycin and teicoplanin. Acetonitrile was added to the teicoplanine to design a modified teicoplanine based electrode. The linear concentration ranges for the proposed enantioselective membrane electrodes were 10−4 to 10−2 mol l−1 for electrodes based on vancomycin and teicoplanin and 10−5 to 10−2 mol l−1 for electrode based on teicoplanin modified with acetonitrile. The slopes of the electrodes were 56.5 mV per pl-carnitine; 54.5 mV per pl-carnitine and 58.3 mV per pl-carnitine for vancomycin-, teicoplanin- and teicoplanin modified with acetonitrile-based electrodes, respectively. The enantioselectivity was determined over d-carnitine. The proposed electrodes could be employed reliably for the assay of l-carnitine raw material and its pharmaceutical formulation, Carnilean® capsules. The surfaces of the electrodes are stable and easily renewable by polishing on alumina paper.