Retention factors of galactose, glucose, trehalose, and maltotriose for a column packed with hydrophobic resins were measured using water as the eluent in the temperature range of 0.5 to 150 . The van't Hoff plots of the retention factors were nonlinear, indicating that hydrophobic interactions between the resin and solutes occurred. The temperature dependence of the retention factor could be analyzed based on Kirfhoff's law and the enthalpy change for distribution was calculated. A high

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... ance liquid chromatography, HPLC, analysis is carried out at an appropriate temperature. The heat labile substances are separated at relatively low temperature. On the other hand, separation of the stable substances is usually performed at room temperature or higher temperature. Separation at high temperature is called high temperature liquid chromatography and is abbreviated as HTLC. Because some physicochemical parameters playing an important role in HPLC, such as viscosity, mobile phase polarity and diffusivity, depend on the temperature, it is known that the temperature is an important factor not only for the stability of the solutes but for their separability. The temperature effect on the distribution behavior in HPLC should be examined for better understanding of the separation phenomena and kinetics. Some reports discuss the temperature dependence of the theoretical plate number [1-4] and the distribution coefficient [5] in HTLC. Furthermore, the temperature dependence of the kinetic parameters of biologically active peptides in the temperature range of -15 to 5 [6], of sugars in the temperature range of 5 to 60 [7], and of amino acids in the temperature range of 20 to 55 [8] has been reported. However, knowledge of the distribution coefficients or the retention factors at much higher temperatures is still insufficient. Water which is extensively used as the eluent of the liquid chromatography is known to show unique features at high temperature under sufficient pressure to maintain its liquid state; e.g., the temperature dependence of the solubility of saturated fatty acids in water at temperatures higher than 160 obeyed the van't Hoff equation but at lower temperatures, the dependence deviated from the equation [9], because the formation of the hydrogen bonds in water largely depends on temperature. This ef fect would play an important role when liquid chromatography, in which the separation occurs mainly by hydrophobic interaction, is conducted using water as the eluent at high temperature. The aim of this study is to measure the retention factors of monosaccharides (galactose and glucose), disaccharide (trehalose), and trisaccharide (maltotriose), which would have moderate hydrophobicity, on the hydrophobic resin using water as the eluent in the temperature range of 0.5 to 150 . Materials and Methods Materials The high temperature endurance column, in which the hydrophobic resin (octadecyl coated; particle diameter, 4 m; pore size, about 25 nm) was packed, (ET-RP1 4D, 150 mm L. 4.6 mm I.D., Shodex, Tokyo, Japan) was used in this study. Deuterium oxide (purity, 99.96%), D-( )-galactose, D-( )-glucose, and maltotriose of analytical grade were purchased from Wako Pure Chemical