Determination of solubilities of uranium complexes in supercritical CO2 by on-line laser-induced fluorescence

A new approach to the measurement of solubilities in supercritical CO2 is reported, utilizing laser-induced fluorescence. This selective technique was found to be capable of rapid multipoint solubility measurements with high sensitivity (10(-9) M). The sensitivity enables measurements to be performed with small amounts of analytes and at low pressure, 80-130 atm, typically below the range of other methods. Four uranyl complexes were investigated using this method, UO2(TTA)2.H20, UO2(TTA)2.TBP, UO2(TTA)2.TOPO, and UO2(NO3)2.2TBP (where TTA = thenoyltrifluoroacetone, TBP = tributyl phosphate, and TOPO = trioctyl phosphine oxide). Comparison with solubility data previously obtained with UV-visible spectroscopy shows good agreement between the techniques. We have shown that the Chrastil solubility equation is equally valid at lower ScF densities, and consequently, solubility values determined at high pressures can be extrapolated to the low-pressure regions and vice versa for solid materials.