O,O,O-trialkyl phosphorothioates as simple and effective ionophores for silver ion-selective membrane electrodes

O,O,O-tris(2-ethylhexyl) phosphorothioate and O,O,O-tributyl phosphorothioate with a thiophosphoryl (P=S) group are simple and effective ionophores to make Ag+-selective membrane electrodes. The electrode based on O,O,O-tris(2-ethylhexyl) phosphorothioate with bis(1-butylpentyl) adipate (BBPA) as a solvent mediator in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to Ag+ in the concentration range of 5× 10-6 to 1×10-2M with a slope of 56mV per decade in a solution containing 0.1M Mg(NO3) 2. The lower limit of detection was 2×10-6M. This electrode showed high selectivity with respect to alkaline, alkaline earth, and heavy metal ions, except for Hg2+, and could be used over a pH range of 3-8.5. Analogous phosphate esters with a phosphoryl (P=O) group, along with O,O,O-tri-o-tolyl phosphorothioate with a P=S group, were less effective as Ag+ ionophores.