Preparation of Phosphate Ion-Selective Membrane Based on Silver Salts Mixed with PTFE or Carbon Nanotubes

A sensitive phosphate sensor has been prepared by constructing a solid membrane disk consisting of variable mixtures of silver phosphate, silver sulfide, and PTFE (Type 1 membrane) or silver phosphate, silver sulfide and nanotube (Type 2 membrane). The ternary membranes exhibit greater selectivity over the wide range of concentration. The membrane with the composition of 50.00% PTFE; 41.66% Ag 3 PO 4 and 8.33% Ag 2 S was selected as our preferred membrane. The membranes exhibited linear potential response in the concentration range of 1×10 –1 to 1×10 –5 M. Their detection limit is about 5×10 –6 M. The membranes have a long lifetime and can be stored in air when they are not in use. The best performance for nanocomposite sensor was obtained with membrane of the following composition: 78.00% Ag 3PO 4 ; 20.00% Ag 2 S, and 2.00% carbon nanoparticles. The membrane had a slope of 32.6 mV toward HPO 4 2- ions in the range between 1×10 -1 and 1×10 -5 M with a detection limit of 5.45×10 –6 M. The proposed sensors were found to be applicable over a pH range between 3 and 7.