ION-SELECTIVE MEMBRANE ELECTRODES FOR THE DETERMINATION OF PYRANTEL WITH LOW PROTEIN INTERFERENCE

A comparison was made of ion-selective poly(vinyl chloride) liquid membrane electrodes for the determination of pyrantel (PY) based on four different ion-pairing agents, viz., tetraphenylborate (TPB), dipicrylaminate (DIPIC), reineckate (REINE) and tungstosilicate (SIWO). The four electrodes showed similar detection limits of 1-2-mu-g ml-1 and nearly the same linear ranges of 1 x 10(-5) - greater-than-or-equal-to 10(-2) mol l-1 for pyrantel in 100 mM sodium phosphate-buffered solutions of pH 7.0. Significant differences between the electrodes were observed in protein-containing solutions. The detection limits of the electrodes with the ion pairs PY-REINE and PY-SIWO were not affected by a background of 6.7 g l-1 (10(-4) mol l-1) bovine serum albumin (BSA), but the PY-TPB- and PY-DIPIC-based electrodes were 6-8 times less sensitive in protein-containing solutions. Of the two protein-insensitive electrodes PY-REINE and PY-SIWO, the latter is advantageous for the determination of PY in biological media as it is about twice as sensitive as the PY-REINE electrode. Inorganic cations did not influence the electrode response even when present in high concentrations, but some lipophilic alkaloids such as berberine and papaverine did.