Nile Red was used as a solvatochromic probe to measure the solvent strength of 85 pure liquids and the results were compared to solvent strength scales from the better known Relchardt's E^) and E^d yes. Nile Red Is also soluble in some pure supercritical fluids and In polar mixtures of supercritical fluids and modifiers. The solvent strength of mixtures of organic modifiers In C02, Freon-13, and Freon-23 was measured as a function of modifier concentration with Nile Red and other solvatochromic dyes. Nile Red exhibits large shifts In the wavelength of Its absorption maximum allowing subtle changes In solvent strength with fluid composition to be quantified, and It Is stable In very strong acids. Relative scales of solvent strength comparing different modifiers added to C02 are presented and compared to a wide range of normal liquids.

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1451Up to 250 000 plates and 298 plates/s were simultaneously observed in nonprogrammed packed column supercritical fluid chromatography. Up to 400 000 or even 667 000 plates appear possible. In programmed runs, substantially higher apparent efficiencies were observed. These results were obtained in spite of repeated assertions in the literature that efficiency in packed column supercritical fluid chromatography has a practical upper limit of 20000 theoretical plates. The simultaneous high efficiency and high speed appear to substantially exceed all previous reports using packed columns and dense fluids.

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