液相色谱梯度洗脱中的谱带压缩效应

谱带压缩效应是梯度洗脱区别于等度洗脱的重要特征。经典的范德姆特(van Deemter)理论塔板高度方程基于等度洗脱推导得到,因此不能对谱带压缩效应进行描述。在梯度洗脱中,保留因子(k)会随流动相组成(φ)的改变而发生变化,这就使得对梯度洗脱机理的研究要比等度洗脱复杂许多。该文对近10年来谱带压缩效应的研究进展,特别是溶剂强度模型(即描述ln k与φ关系的数学表达式)的非线性特征对谱带压缩因子(G)的影响进行了述评,指出为了更好地认识谱带压缩效应需要将这种非线性因素考虑在内。

Effects of peak compression in gradient elution of liquid chromatography

Peak compression is a unique feature of gradient elution and is non-existent in isocratic elution.Since the classical plate height equation,which is also called as van Deemter equation,is derived by assuming isocratic elution,it cannot be used to account for the effects of peak compression.As opposed to the case of isocratic elution,the retention factor(k)varies with the mobile phase composition(φ)under gradient elution,thereby complicating mathematical analysis.Herein,the research progress on peak compression in the past decade,especially the effect of the nonlinear feature of solvent strength models(i.e.,expressions for ln k vs.φ),is reviewed.A general expression for the peak compression factor(G)is introduced,for which the variation in plate height(H)withφis ignored.Based on this equation,the classical equation for G,which was first proposed by Poppe and assumes the linear solvent strength model(LSSM)and linear gradient elution,can be derived.The effects of pre-elution of the solute in the initial mobile phase on G,which are attributed to the dwelling time of the system,are included in the Poppe equation.When the solvent strength model is nonlinear,e.g.,the quadratic solvent strength model(QSSM),the analytical expressions for G can also be obtained from the general expression.Under ideal chromatographic conditions,where H=0 and the adsorption isotherm is linear,the peak compression is determined by the ratio of the retention factor of the solute in the initial mobile phase to that at the eluted mobile phase composition.