Adjusting selectivity in liquid chromatography by use of the thermally tuned tandem column concept

In this study, we propose the novel 'thermally tuned tandem column (T³C)' concept for the optimization of selectivity in LC by continuous adjustment of the stationary phase. Two columns with distinctly different chromatographic selectivities (e.g., polybutadiene- and carbon-coated zirconia) are serially coupled and independently temperature-controlled. Selectivity is 'tuned' by adjusting the individual temperatures of the two columns. The effect of changing column temperature is quite analogous to changing the relative column lengths, thereby altering the relative and absolute contribution each column makes to the overall retention time in T³C. The distinct selectivity differences between polybutadiene- and carbon- coated zirconia as well as the extraordinary thermal stability of zirconia- based phases (thermally stable to 200 °C) allow us to tune the overall chromatographic selectivity over a very substantial range. We have developed a simplified useful model, which characterizes retention and selectivity for the T³C system as a function of the two column temperatures. The model is in good agreement with the experimental results. We also describe a simple computer-assisted optimization strategy based on the window diagram method, which facilitates the optimization of the T³C system with only four or five initial runs.