Solubility measurements of noble metal acetylacetonates in supercritical carbon dioxide by high performance liquid chromatography (HPLC)

A method has been developed for measuring the solubility of noble metal acetylacetonates by the direct injection of the supercritical carbon dioxide (scCO2) solution into a high pressure liquid chromatograph. We found the use of (1) reverse phase high pressure liquid chromatography (RP-HPLC) to separate the sample peak from the noise peak on chromatogram and (2) a scCO2-philic eluent to eliminate the noise peak, to be effective. Using this improved method, we measured the solubilities of noble metal complexes of Pt, Pd, Ru, Rh and Ag acetylacetonates in scCO2 from 10 to 30 MPa at 313 K. Measurements were conducted with smaller amounts of samples (less than 0.1 g) and with shorter experimental times than by the standard dynamic flow method. The molar fraction y2 was of the order 10−5 to 10−4 for Ru and Rh acetylacetonate, 10−5 for Pd and Pt acetylacetonate, and 10−7 for Ag acetylacetonate. The solubility data for Pd, Pt, Ru, and Rh acetylacetonates were successfully correlated using the Chrastil model.