Construction of ion selective membrane electrodes for the potentiometric determination of enalapril maleate in its pure form and pharmaceutical preparations

Abstract

Two novel enalapril maleate (ENM) ion selective electrodes were constructed
and used for the determination of ENM in its pure form and pharmaceutical
formulations. The electrodes were based on the use of the ion association complexes
of either phosphotungstic acid (PTA) or phosphomolybdic acid (PMA) as anions with
Enalapril cation in a PVC matrix plasticizers with di-butyl phthalate (DBP). The
results of these electrodes showed stability (life time 33 and 51 days), near Nernstian
response (slope 57.2 and 52.2 mV/decade ), low detection limit (1.3×10-7 and 4.2×10-7
M ) for DBP-ENM-PTA and DBP-ENM-PMA electrodes respectively. For both
electrodes the best concentration for internal filling solution was 1×10-3 M ENM and
the linear range was 1×10-5- 1×10-1 M. The electrodes were found to be usable within
the pH range 2.2 – 3.8 and 2.5 – 3.0 for the above mentioned electrodes. This study
also included the measurements of selectivity of these electrodes in the presence of
common cations, anions and some drug excipients. The KPot
i ,J found to be less than 1.
The electrodes were successfully applied for determination of ENM in pure form and
in tablet pharmaceutical preparation with recovery of not less than 98 %.