Two metformin carbon paste and PVC electrodes are proposed for the determination of metformin. Different methods for electrode fabrication (including formation of the ion pair in situ, soaking of the electrode in the ion pair aqueous solution, in addition to the classical modification of the electrode matrix with the ion pair) are described for both carbon paste and PVC electrodes. Electrodes based on in situ ion pairs of metformin with sodium tetrakis (4-fluorophenyl) borate or tungstophosphoric acid respectively showed the best performance compared with the other methods of preparation. These electrodes exhibit a linear response with a good Nernstian slope over a concentration range 10-5-10-1 M of metformin in a working pH range between 4 and 8. The effect of the electrode matrix composition and plasticizer on the performance of both carbon paste and PVC electrodes are investigated for each fabrication method. The proposed technique was applied successfully for the determination of metformin in pure solutions and in dosage forms with good accuracy and precision. The results were compared statistically with those given by the reported method.
Keywords: Ion selective electrode, Metformin, PVC Membrane, Carbon paste, In situ, Pharmaceutical preparations
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