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

Abstract

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 −2 M with a slope of 56 mV per decade in a solution containing 0.1 M Mg(NO 3) 2. The lower limit of detection was 2×10 −6 M. This electrode showed high selectivity with respect to alkaline, alkaline earth, and heavy metal ions, except for Hg 2+, 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.