Using PVC ion-selective electrodes for the potentiometric flow injection analysis of distigmine in its pharmaceutical formulation and biological fluids

The construction and electrochemical response characteristics of poly(vinylchloride) (PVC) membrane selective electrodes for the determination of distigmine (Ds) are described. The sensing membrane comprised an ion-pair based on distigmine phosphomolybdate (Ds-PM), distigmine phosphotungstate (Ds-PT), distigmine silicomolybdate (Ds-SM), distigmine silicotungstate (Ds-ST), distigmine tetraphenylborate (Ds-TPB), and distigmine reineckate (Ds-Rein) in a plasticized PVC matrix with dioctylphthalate (DOP). The influence of membrane composition on the electrodes’ response was studied. The electrodes showed a fast, stable and Nernstian response over a wide distigmine concentration range 5.0 x10^-7 –1 x10^-2 mol L^-1 with a slope of ~30.5 ± 1.0 mV dec^-1. The response is independent of the pH of test solution within the range 3.8–10.5. The life span of the electrodes extends to at least 2 months without any considerable divergence in potential and has a fast response time of 15 s. The electrodes showed good selectivity towards distigmine with respect to large numbers of ions in batch and FIA systems. The electrodes have been applied to the determination of distigmine in pure solution, pharmaceutical compound and human urine. The dissolution profile for Ubretid tablets (5 mg/tablet) was studied.