New aminophosphonic acid extractants, alpha-(4-n-octylanilino)benzylphosphonic acid monobutyl ester (OABPM) and alpha-dodecylaminobenzylphosphonic acid monobutyl ester (DABPM) with different amino moiety basicities were synthesized to examine the effect of the basicity on their extraction selectivities for In(III), Ga(III), Zn(II), Cu(II), Se(IV) and Se(VI). The extraction order for metals using OABPM was In(III) > Ga(III) > Cu(II) > Zn(II), while Se(IV) and Se(VI) were not extracted. On the other hand, DABPM exhibited the reverse extraction order for Cu(II) and Zn(II). The mutual separation ability of DABPM for these metals was higher than that of OABPM as is determined by the basicity of the amino moiety of their extractants. The extraction equilibria for Ga(III) and Zn(II) with OABPM and DABPM were discussed using slope analysis. It was observed that only Ga(III)- and Zn(II)-DABPM complexes contained nitrate ions, because the phosphonic acid moiety of DABPM was hard to participate in the metal extraction. (C) 2016 Elsevier B.V. All rights reserved.