Mixed trialkyl phosphine oxides (TRPO) are promising extractants. They may be used to recover radionuclides from highly radioactive liquid wastes. However, since TRPOs contain alkyl chains ranging from C4 to C8, different TRPO may have different characteristics. In this paper, four TRPOs from different sources are compared. The extraction and back-extraction characteristics for UO22+, Pu4+, Am3+, and TcO4- were investigated. and the loading capacities for both Of UO22+ and HNO3 were compared. Infrared spectroscopy and pyrolysis gas chromatography were used to analyze the type and composition of the side-group in these TRPOs. The experimental results demonstrate that different TRPOs possess similar extraction and back-extraction characteristics because they have the same type of side-group. However, different TRPOs show different loading capacity for UO22+ and HNO3 due to differences in the alkyl composition of the side-group. (C) 2003 Elsevier Science B.V. All rights reserved.