Iron ion-selective electrodes for direct potentiometry and potentiotitrimetry in pharmaceuticals

The compositions and general performance characteristics of four PVC membrane sensors respective to iron were described. Three of these sensors are based on the use of ion association complexes of iron(II) 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) with tetraphenylborate (TPB) or phosphotungstic acid (PTA) as novel electroactive materials dispersed in dibutyl sebacate plasticizer on glass assemblies and solid state graphite support. The fourth sensor is based on plasticized carboxylated poly(vinyl chloride) (PVC) matrix membrane. The developed sensors were used for the assay of iron in some pharmaceutical preparations. The sensors displayed a rapid and linear response for the doubly charged iron over the concentration range from 5×10-7 to 10-2M. The pH does not affect the sensor performances within the pH range 3.2-7.1. Acceptable selectivity was obtained for iron against many inorganic cations, sugar and aminoacids. The constructed sensors were used as indicator electrodes in potentiometic titration of [Fe(TPTZ)2]2+ with tetraphenylborate solution in standard and various pharmaceutical forms. The sensors can be used for more than 3 months without observing any deviations.