Tip #265: Calculations for Gradient Polymer Elution Chromatography (GPEC)

Welcome back! In this week’s tip for Empower Chromatography Data System (CDS), we will learn about calculations for Gradient Polymer Elution Chromatography (GPEC). In last week’s tip, we worked with derivatives of UV spectra and also learned about the Splining function, Tip #264.

Let’s start with some background information. GPEC is an LC technique. In this example, chromatograms in Figure 1, three chemically different polymers co-elute using a GPC separation because they have similar hydrodynamic volumes. If reverse phase separation is used to separate these polymers, they would remain partially soluble throughout the separation and would not be baseline separated. The GPEC method purposefully precipitates the polymers onto the column or column frit until the gradient ratio of good solvent reaches the polymers solubility point, thereby releasing the polymer from the surface of the column. Instead of using the size-based separation of GPC, the polymers are separated by their chemical solubility using GPEC.

figure 1

Practical examples where GPEC is helpful:

• Reverse engineering
• Batch to batch conformity
• Optimization of co-extrusion or formulation
• Aligning thermal properties with a chemical analysis

Our goal is to calculate the percentages of solvent used in the mobile phase to separate the polymers.

Let’s get started.

Step 1

We begin with the gradient table in the Instrument Method. The method starts with 100% methanol and ends at 100% THF (figure 2).

figure 2

Step 2

On the Data tab of the Instrument Method, select the solvent lines with the solvents used in the gradient (figure 3).

figure 3

Step 3

The polymers are separated, and we record the retention time of each (figure 4).

figure 4

Step 4

Peak Custom Fields are created to report the ‘y’ value at the retention times determined in Step 3 (figure 5).

figure 5

Step 5

The ‘%A’ channel has been processed and we see the ‘%methanol’ at which each polymer elutes (figure 6).

figure 6

Step 6

The ‘%C’ channel has been processed as well and we the ‘%THF’ at which each polymer elutes (figure 7).

figure 7

It’s that easy!

Final Note: This can be done with either the Pro or QuickStart interface.

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Next time in Empower Tip #266– we will answer an Empower user question on Control Charts.

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