Investigation of the low temperature effect in micro high performance liquid chromatography‐open tubular microcapillary column

Abstract

The experimental results are represented in Figure 1 ; as in ref.[5], the log k'and Csaxes have opposite directions. Although only few values of solubility are available, the variations of log kvalues and log CS values of 2-hydroxynaphthalenc? are clearly seen to be parallel; some deviations are observed for the less accurately known low K and high Cs values. For 2,3-dihydroxynaphthalene only two Cs values are available in the range of good accuracy, so thatonlyageneral ideacan begainedoftheanalogiesoflog K and log Cs; however, the vertical distance between the plots is clearly much larger than for 2-naphthol. This is in accord with earlier observations [3]. The retention vs. eluent composition relationships are approximately linear, as is frequently observed for liquidlliquid and liquidlsolid systems of this type [7,8].The experimental results confirm the important role of solution effects for nonpolar adsorbents [4,9-141; however, for polar solutes the selectivity (A log K) is apparently attributable not only to differences of solubility (A log CS) but also to other factors.

Comparison of the Characteristics of Adsorption Equilibrium and Surface Diffusion in Liquid−Solid and Gas−Solid Adsorption on C18-Silica Gels

“…The single straight line in Figure suggests that there is an enthalpy−entropy compensation (EEC) for adsorption equilibrium, irrespective of the mobile phase used, whether a solution or a gas. Numerous reports have shown an EEC for the retention behavior of various compounds in other RPLC systems ,,,,,,− and demonstrated its possibility on theoretical bases. − Similar compensation phenomena have also been reported for the retention behavior in other systems such as ion-pair LC, , ion-exchange LC, and in gas chromatography. ,

3 Enthalpy−entropy compensation of adsorption equilibrium.

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Separation of isotopically labeled molecules by micro high performance liquid chromatography with a packed micro glass capillary column

“…These examples would suggest that high performance liquid chromatography is unable to compete with gas chromatography for the separation of isotopic molecules. However, a recently developed micro high performance liquid chromatography technique [7,8] of very high efficiency opens up the possibility using liquid chromatography for high resolution separations of isotopically substituted molecules.…”

Thermodynamic Interpretation of Retention Equilibrium in Reversed-Phase Liquid Chromatography Based on Enthalpy−Entropy Compensation

“…Mechanistic similarities of retention behaviors in RPLC were discussed on the basis of the enthalpy−entropy compensation (EEC) between Δ H and Δ S . Numerous publications demonstrated experimentally an EEC − or supported the possibility of EEC on theoretical bases. − Compensation temperatures ( T c ) between about 500 and 1000 K were reported under different experimental conditions involving the mobile-phase solvents, the sample compounds, and the temperature range. ,,,− , That an EEC exists suggests that the retention behavior is governed by a single mechanism. EEC was also found in normal-phase LC systems (NPLC), using a polar stationary phase (e.g., Permaphase ETH) and a nonpolar solvent (e.g., hexane with 1% ethanol).…”

“…Mechanistic similarities of retention behaviors in RPLC were discussed on the basis of the enthalpy-entropy compensation (EEC) between ∆H and ∆S. Numerous publications demonstrated experimentally an EEC [5][6][7][8][9][10][11][12][13][14][15][16][17][18] or supported the possibility of EEC on theoretical bases. [19][20][21][22][23] Compensation temperatures (T c ) between about 500 and 1000 K were reported under different experimental conditions involving the mobile-phase solvents, the sample compounds, and the temperature range.…”