UV−Visible Spectroscopic Measurement of Solubilities in Supercritical CO2 Using High-Pressure Fiber-Optic Cells

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Abstract
The design and construction of a microscale, fiber-optics-based system for the measurement of solubilities in supercritical CO(2) 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, UO(2)(tta)(2)·TBP, in supercritical CO(2) 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 CO(2). Also, the small volume of this system allows solubilities to be measured with relatively small amounts of compounds.