Background The application of an ion selective technique for the determination of analyte concentrations
is considered one of the most economical techniques for quality control purposes.
Objective To elaborate and investigate the construction and general performance characteristics of potentiometric
PVC membrane sensors for venlafaxine cation (Ven+).
Method The sensors are based on the use of the ion association complexes of the venlafaxine cation with phosphotungstate
(PT) and silicotungstate (ST) counter anions as ion exchange sites in the plasticized PVC matrix.
They are characterized by potentiometric and conductimetric measurements, performed under various conditions.
Results The electrodes showed a fast (response time around 15 s), stable (life span 45 days) and linear (r2 0.995)
response for venlafaxine over the concentration range of 5x10-5 - 1x10-2 M venlafaxine hydrochloride. The solubility
product of the ion pair and the formation of the precipitation reaction leading to the ion pair, were determined
conductimetrically. The electrodes were found to be very selective, precise (RSD < 1%) and applicable to
the potentiometric determination of venlafaxine hydrochloride in pure solutions or in pharmaceutical preparation
and in biological fluid (serum), without any interference. Validation of the method shows the suitability of the
proposed electrodes for use in the quality assessment of venlafaxine hydrochloride.
Conclusion Using only a pH meter in combination with the selective electrodes, drug substance or drug product
could be determined accurately in a few seconds. In addition, the in-house made electrodes were tested to monitor
venlafaxine in serum. Acceptable results were achieved using the standard addition technique.