Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, 1, Sec. 3, Zhongxiao E. Rd., Taipei, 10608 Taiwan.
Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, 1, Sec. 3, Zhongxiao E. Rd., Taipei, 10608 Taiwan.
J Chromatogr A. 2018 Jun 29;1556:64-72. doi: 10.1016/j.chroma.2018.04.065. Epub 2018 Apr 27.
The mobile phase, when used in combination with a polysaccharide-based sorbent, often contains hydrocarbons with polar modifiers. Studies have investigated the effect of solvent on the recognition mechanism of polysaccharide-based sorbents, but it remains unclear how these modifier molecules affect solute retention behavior. This study used an amylose 3,5-dichlorophenylcarbamate-based sorbent to systematically investigate the retention behavior of various solutes as a function of the concentration of four polar modifiers: ethanol, isopropanol, methyl tert-butyl ether, and acetone. The thermodynamic properties of adsorption for the four modifiers were thoroughly investigated using retention factor data, van't Hoff plots, and adsorption isotherms of the modifier molecules. The adsorption data of acetone and isopropanol followed the Langmuir isotherm, whereas the bi-Langmuir isotherm more accurately fit the ethanol data. For methyl tert-butyl ether, the Brunauer-Emmett-Teller adsorption isotherm indicated multilayer adsorption with a low saturation capacity of the first adsorption layer. A multivalent retention model interpreted slopes of the plots of the logarithm of the retention factor versus the logarithm of the modifier concentration. Because the molecular polarity of acetone is stronger than that of methyl tert-butyl ether, the limiting absolute slope values of tetrahydrofuran at a very high acetone modifier concentration were smaller than that when methyl tert-butyl ether was used as the polar modifier. The higher absolute value of the slope for tert-butanol suggested the potential of CO groups of acetone molecules to form bifurcated H bonds on a tert-butanol molecule. When alcohol was employed as the polar modifier, the results suggested that the effect of isopropanol self-association on the retention factor was stronger than the effects of solute-IPA complexation and isopropanol adsorption. For alcohol modifiers, U-shaped retention curves were obtained for all aromatic solutes. When acetone or methyl tert-butyl ether was used, the absence of a U-shaped curve indicated the weak polarity of those modifiers.
流动相，当与多糖基固定相结合使用时，通常含有带有极性修饰剂的碳氢化合物。研究已经考察了溶剂对多糖基固定相识别机制的影响，但仍不清楚这些修饰分子如何影响溶质保留行为。本研究使用基于直链淀粉 3,5-二氯苯甲酰基的固定相，系统地研究了各种溶质在四种极性修饰剂（乙醇、异丙醇、甲基叔丁基醚和丙酮）浓度下的保留行为。通过保留因子数据、范特霍夫图和修饰剂分子的吸附等温线，彻底研究了四种修饰剂的吸附热力学性质。丙酮和异丙醇的吸附数据符合朗缪尔等温线，而乙醇数据更准确地符合双朗缪尔等温线。对于甲基叔丁基醚，BET 吸附等温线表明存在多层吸附，且第一层吸附的饱和容量较低。多元保留模型解释了以保留因子的对数对修饰剂浓度的对数作图的斜率。由于丙酮的分子极性强于甲基叔丁基醚，因此在非常高的丙酮修饰剂浓度下，四氢呋喃的极限绝对斜率值小于使用甲基叔丁基醚作为极性修饰剂时的值。叔丁醇斜率的绝对值较大表明，丙酮分子的 CO 基团有形成叔丁醇分子上的分叉氢键的潜力。当使用醇作为极性修饰剂时，结果表明异丙醇自缔合对保留因子的影响强于溶质 IPA 络合和异丙醇吸附的影响。对于醇修饰剂，所有芳香族溶质都得到了 U 形保留曲线。当使用丙酮或甲基叔丁基醚时，由于这些修饰剂的极性较弱，因此没有 U 形曲线。
