Inverse supercritical fluid chromatography (ISFC) is used to
measure partition coefficients of
five polar and nonpolar organic solids between supercritical
CO2 and cross-linked poly(dimethylsiloxane) (PDMS) swollen with CO2.
Polymer−solute interaction energies, which are
determined from the partition coefficients, correlate with the heats of
vaporization of the pure
solutes. These interaction energies can be determined at ambient
temperature for solutes that
are too nonvolatile to study by inverse gas chromatography. Binary
and ternary phase equilibria
are modeled with lattice fluid theory including a term to account for
the degree of polymer cross-linking. Experimental results indicate that solute adsorption on
the support phase, which can
be severe in packed columns, is negligible with the use of capillary
columns.
A compact, inexpensive detector for proteins has been constructed based on two-photon excitation of fluorescence from phenylalanine, tyrosine, and tryptophan. The fluorescence was excited by a solid-state microchip laser operating at 532 nm. Detection limits for phenylalanine, tyrosine, and tryptophan were 62 microM, 2.0 microM, and 470 nM, respectively, in a volume of 3 fL. The detection limit for a test protein, bovine serum albumin, was 130 nM.
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