Gradients, Peak Shapes and the Making of Chromatography

Eli Grushka, Institute of Chemistry, The Hebrew University, Jerusalem, Israel
Tzipora Ben Tzvi , Institute of Chemistry, The Hebrew University, Jerusalem, Israel

In our efforts to understand the dependency of the chromatographic peak shape on the properties of mobile phase gradients in HPLC, we have developed a stochastic simulation to follow the behavior of the solutes molecules during the chromatographic process.  The stochastic simulation is based on the mass-balance equation that takes into account the main process leading to zone broadening; namely, molecular diffusion, mobile phase velocity profiles and the portioning process of the solutes between the two phases.  The stochastic simulation approach is particularly powerful since it allows us to follow each molecule of the solutes injected to the column and see how they progress down the column as the separation proceeds.  As an example we will show the simulation of the separation of two solutes.

The stochastic simulation provides us with the means of following the formation of the solute zone in the column and to calculate the peak's parameters, in particular the skew of the peak, as the solute elutes from the column.  The skew is a peak parameter that measures the peak symmetry.  Our simulations show that the skew is a function of (1) the gradient start time, (2) the gradient steepness, (3) the partition coefficient and (4) of the mobile phase velocity.  Based on the simulation we can predict the gradient conditions that will not affect greatly the peak shape.