UV-visible spectroscopic measurement of solubilities in supercritical CO2 using high-pressure fiber-optic cells

The design and construction of a microscale, fiber-optics-based system for the measurement of solubilities in supercritical CO2 by UV−visible spectroscopy is described. This system consists of three high-pressure fiber-optic cells, with path lengths ranging from 38 μm to 1 cm, constructed from standard 1/16-in. stainless steel fittings and silica fibers. It is capable of withstanding pressures in excess of 300 atm, and spectra over the entire UV−visible range (200−900 nm) can be obtained. Use of three cells with different path lengths enables compounds of high or low solubility to be measured over a concentration range of several orders of magnitude. The solubility of a uranium complex, UO2(tta)2·TBP, in supercritical CO2 at 40 °C and over the pressure range 100−325 atm was determined, and it was found to be possible to attain solubilities in excess of 10-2 M for metal species in unmodified supercritical CO2. Also, the small volume of this system allows solubilities to be measured with relatively small am...