STATIC SECONDARY IONIZATION MASS-SPECTROMETRY ANALYSIS OF TRIBUTYL-PHOSPHATE ON MINERAL SURFACES - EFFECT OF FE(II)

The static secondary ionization mass spectrometry (SIMS) spectrum of tri-n-butyl phosphate (TBP) on a variety of basalt and quartz samples is affected by the chemical composition of the mineral surface. When TBP is adsorbed on Fe(II)-bearing surfaces, the compound undergoes concomitant H- abstraction and reduction, followed by the elimination of two C4H8 molecules to form an ion at m/z 137(+). When TBP is adsorbed to quartz or other nonreducing surfaces, it merely undergoes protonation and elimination of three C4H8 molecules to form H4PO4+. When TBP is adsorbed to Fe(III)-bearing surfaces, it undergoes H- abstraction and elimination of two C4H8 molecules, to form an ion at m/z 153(+). These conclusions are supported by model studies that employed FeO, Fe2O3, TBP, and tributyl phosphite. The results show that the SIMS spectrum is very sensitive to the mode of TBP adsorption on the mineral surface.