8-Quinolyl dihydrogen phosphate, 1-naphthyl dihydrogen phosphate and monosodium 8-quinolyI methyl phosphate were synthesized. Extensive potentiometric investigations were made of the equilibrium complexation of the three anions, 8-quinolyl phosphate (1), 1-naphthyl phosphate (2), and 8-quinolyl methyl phosphate (3) with hydrogen, copper(II), zinc(II), nickel(II) and cobalt(II) ions in aqueous solution at 25[ddot]C and 1 α I50mmoldm-3(Na+) [Cl-1. Equilibria between 1 and manganese(II) ions were also studied. The protonation equilibrium results augmented by NMR measurements were interpreted as indicating that the first proton to be bound by 1 becomes shared between the quinolinium nitrogen and a phosphate oxygen. The metal complexation results indicated the formation of the mononuclear binary complex, ML, in each case. In addition, copper(II), zinc(II) and nickel(II) ions formed the hydroxo complex, MLH-1, with 1,2, and 3. Zinc(II)also formed the protonated complex, ZnLH with 1. Also with L α 1, CuLH-1, ZnLH-1and ZnLH were found to be very significant complexes whereas NiLH-1was found only in relatively low concentrations.