Tris(2-ethylhexyl) phosphate and tricresyl phosphate as new neutral carriers for organic ammonium ion-selective membrane electrodes

Phosphate esters, such as tris(2-ethylhexyl) phosphate (TEHP) and tricresyl phosphate, can be used as neutral carriers to make organic ammonium ion-selective membrane electrodes. For example, a hexylammonium ion-selective electrode was constructed using TEHP as the carrier and dioctyl phthalate as a membrane solvent in a poly(vinyl chloride) membrane matrix. The electrode exhibited a near-Nernstian response to hexylammonium in the concentration range from 2×10−4 to 0.1 M with a slope of 57 mV per concentration decade. The lower limit of detection was 2×10−5 M, was comparable to that of the electrode made from one of the amine ionophores, a calix[6]arene analog, reported previously. The interaction between the phosphate ester and hexylammonium was confirmed by 1H-NMR spectroscopy.