The distribution of 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ), a polydentate neutral donor ligand, alone or in the presence of heterocyclic beta-ketoenol extractants (HL or HL-10-LH): 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HPMBP), 1,12-bis(1 '-phenyl-3 '-methyl-5 '-hydroxy-4 '-pyrazolyl)-dodecane-1,12-dione (HL-10-LH), 3 -phenyl-4-benzoyl-isoxazol-5-one (HPBI) or 3-phenyl-4-p-tert-butylbenzoyl-isoxazol-5-one (HPtbBI), between a chloroform phase and a nitric aqueous phase [(Na,H)NO3] = 0.1 M has been studied. The TPTZ partition constant and the speciation of the TPTZ species at various pHs have been determined. The stoichiometries of the interaction complexes have been proposed and the corresponding interaction constants have been calculated. (c) 2006 Elsevier B.V. All rights reserved.