Skeptical of ProEZGC’s new PLOT capabilities? We thought you might be

Perhaps you just read about the recent addition of PLOT columns to the ProEZGC platform. You may have been wondering, why were PLOT capabilities absent from our ProEZGC platform for so long? PLOT (porous layer open tubular) and WCOT (wet layer open tubular) columns separate compounds based on two different principles: adsorption (PLOT) and absorption (WCOT). In adsorption-based chromatography, analytes interact primarily with the surface of the phase material, but in absorption base chromatography, analytes actually dissolve in and out of the phase material. This contributes to notable differences in peak shape, loading capacity, and analyte retention between the two phase types.

ProEZGC was initially developed with WCOT columns in mind, producing accurate models based on absorption chromatography. However, we had received feedback in the past from our method translator, suggesting the physics might not hold up for PLOT’s adsorption-based chromatography.  Even though we found the method translations to be accurate, it shone a critical light on PLOT vs WCOT modeling. So, let’s take a peek at some comparisons between empirical and modeled data under changing conditions…

In this experiment, we see how well ProEZGC modeled a collection of 21 compounds under varying conditions on the Rt-Alumina BOND/Na₂SO₄. In this experiment, we started with a simple ramp method: 40^oC (hold 1 min), ramp at 7^oC/min to 195^oC (hold 10 min), 8psi, helium, constant pressure. Oven conditions were then changed one by one, so we could capture which oven parameters were most impactful for the modeler. These oven parameters included a higher constant pressure, higher and lower starting temperatures, higher and lower ramp rates, an alternative carrier gas, and a combination of changing hold times, ramp rate, and carrier gas. A ‘lower PSI’ is not shown here because it was evaluated in a separate experiment.

Figure 3: Average relative difference between the model and empirically obtained data, under varying GC conditions. Error bars represent standard deviation of the average.

No matter what parameter we changed, the average relative difference (|RT_model-RT_­empirical|/RT_empirical) of the model was within 10% of the empirically measured retention times. In this experiment, increasing the starting temperature had the greatest effect on the accuracy, but across the 21 compounds, average relative difference was still well within 5%. Additional experiments evaluated varying column dimensions, different compound classes, and different column phases, all demonstrating a similarly high degree of accuracy.

So, whether you’re using a PLOT or WCOT column, ProEZGC will save you time and resources by virtually modeling a variety of oven conditions, detectors, and column dimensions that could affect your chromatography.

If you are interested in learning more about PLOT columns and their importance in gas chromatography, check out this 2010 LCGC article from Ronald E. Majors and Jaap de Zeeuw.