Potentiometric determination of polyether ionophores growth promotors in animal feed preparations

The construction and electrochemical response characteristics of four polyvinylchloride (PVC) membrane sensors for the determination of monensin (MN) and salinomycin (SL) were described. The membranes were prepared using 1 wt.% drug, 44 wt.% nitrophenyl octyl ether, 53 wt.% PVC and 2 wt.% lipophilic additive which is the anionic potassium tetra (4-chlorophenyl) borate in sensors 1 and 2 and the cationic nicklo-phenanthroline in sensors 3 and 4. Sensor 1 and sensor 2 show linear responses over concentration range of 10(-3)-10(-5) M drug with cationic slopes of 52.3 and 54.1 mV per concentration decade, respectively. On the other hand sensor 3 and sensor 4 show linear responses over concentration range 10(-4)-10(-5) M drug with anionic slopes of 28.1 and 29.7 mV per concentration decade, respectively. The 4 sensors were successfully applied to the determination of MN and SL in their pharmaceutical products (Premix) with average recoveries of 98.4-100.4+/-2.41-1.97% for sensors 1 and 2 and 97.6-98.8+/-3.16-3.07% for sensors 3 and 4. The obtained results were compared reasonably well with the data obtained using the USP method (2000). The proposed sensors were also applied for the direct determination of both drugs in animal feed preparations without prior treatment in low levels; 10-1000 microg per 5 g feed. The sensors were successfully used to follow up the drugs concentration in the presence of other growth promotors, other antibiotics and the coexisting fatty acids.