Departament de Química Analítica, Universitat de València, c/Dr. Moliner 50, 46100 Burjassot, Spain.
J Chromatogr A. 2011 Aug 5;1218(31):5166-74. doi: 10.1016/j.chroma.2011.05.086. Epub 2011 May 30.
The chromatographic elution has been studied from different perspectives. However, in spite of the simplicity and evident deficiencies of the plate model proposed by Martin and Synge, it has served as a basis for the characterization of columns up-to-date. This approach envisions the chromatographic column as an arbitrary number of theoretical plates, each of them consisting of identical repeating portions of mobile phase and stationary phase. Solutes partition between both phases, reaching the equilibrium. Mobile phase transference between the theoretical plates is assumed to be infinitesimally stepwise (or continuous), giving rise to the mixing of the solutions in adjacent plates. This yields an additional peak broadening, which is added to the dispersion associated to the equilibrium conditions. It is commonly assumed that when the solute concentration is sufficiently small, chromatographic elution is carried out under linear conditions, which is the case in almost all analytical applications. When the solute concentration increases above a value where the stationary phase approximates saturation (i.e. becomes overloaded), non-linear elution is obtained. In addition to overloading, another source of non-linearity can be a slow mass transfer. An extended Martin and Synge model is here proposed to include slow mass-transfer kinetics (with respect to flow rate) between the mobile phase and stationary phase. We show that there is a linear relationship between the variance and the ratio of the kinetic constants for the mass transfer in the flow direction (τ) and the mass transfer between the mobile phase and stationary phase (ν), which has been called the kinetic ratio (κ=τ/ν). The proposed model was validated with data obtained according to an approach that simulates the solute migration through the theoretical plates. An experimental approach to measure the deviation from the equilibrium conditions using the experimental peak variances and retention times at several flow rates is also proposed.
从不同的角度研究了色谱洗脱。然而，尽管 Martin 和 Synge 提出的板模型简单且明显存在缺陷，但它至今仍是柱特征化的基础。这种方法将色谱柱设想为任意数量的理论板，每个理论板由相同的移动相和固定相重复部分组成。溶质在两相之间分配，达到平衡。假定移动相在理论板之间的转移是无穷小的分步（或连续的），导致相邻板中的溶液混合。这会导致额外的峰展宽，这与平衡条件下的分散有关。通常假设当溶质浓度足够小时，色谱洗脱是在线性条件下进行的，这几乎是所有分析应用的情况。当溶质浓度增加到固定相接近饱和（即过载）的值以上时，会得到非线性洗脱。除了过载之外，非线性的另一个来源可能是传质缓慢。这里提出了一个扩展的 Martin 和 Synge 模型，以包括移动相和固定相之间传质动力学（相对于流速）的缓慢。我们表明，在流动方向上的传质动力学常数（τ）和移动相和固定相之间的传质动力学常数（ν）之间存在线性关系，这被称为动力学比（κ=τ/ν）。该模型通过根据模拟溶质通过理论板迁移的方法获得的数据进行了验证。还提出了一种使用实验峰方差和在几个流速下的保留时间来测量偏离平衡条件的实验方法。
