Potentiometric carbon paste electrodes for the determination of bismuth in some pharmaceutical preparations

The construction and general performance characteristics of two novel potentiometric membrane sensors responsive to bismuth are described. The sensors are based on the use of ion-association complexes of tetraiodobismate(III) (TIB) anion with polyoxyethylene(10) octyl phenyl ether (1) and tris(1,10-phenanthroline)iron(II) (2) as exchange sites in a carbon paste matrix. The sensors show fast, stable, and near-Nernstian response for the mono-charged anion of tetraiodobismate(III) over the concentration range 1 x 10(-3)-1 x 10(-6) mol dm(-3) at 25 degrees C over the pH range 4.0-9.0 and 3.0-8.0 with an anionic slope of 51.5 +/- 0.5 and 53.0 +/- 0.4 per concentration decade for tetraiodobismate(III)-1 and -2 (sensor-1 and sensor-2), respectively. The lower detection limit was 4 x 10(-6) and 2 x 10(-6) mol dm(-3) with a response time of 20-40 s for sensor-1 and sensor-2 in the same order. The selectivity coefficients for bismuth relative to a number of interfering anions and iodide complexes of some metal ions were investigated. Direct potentiometric determination of 1-200 mu g cm(-3) of bismuth in aqueous solution showed an average recovery of 98.4% and a mean relative standard deviation of 1.5% at 80.0 mu g cm(-3). The determination of bismuth(III) in suppositories and ointment dosage form in the present study was comparable with the British pharmacopoeia method.