Empower Tip: Working with GPC/SEC data in Empower

In this tip we will learn about universal calibration using Mark-Houwink constants (k and alpha).

The advantages to this technique are it is an easy and accurate method, you can use one calibration curve for different types of polymers, and you can determine the intrinsic viscosity of a polymer. The disadvantage is that the accuracy of the results depends on the accuracy of the Mark-Houwink constants.

Let’s see how it’s done!

Bring the Sample Set into the Alter Sample window and click the Amounts tool. Change the SampleSet Type to Standards & Unknowns.

STEP 2Click the K-Alphas tab. Enter the Ks and Alphas for the standards and samples. You can find these values in polymer handbooks and/or Google them.

STEP 3Create a Processing Method and on the Calibration tab, select Universal for the GPC Technique.

STEP 4After processing the Sample Set, we see the result for a sample. The calculation of Mv and [n]P (the intrinsic viscosity) are done in addition to the other molecular weight calculations.

STEP 5The calibration curve plots Retention Time on the x-axis versus Log(MolWt[n]) on the y-axis to reflect the addition of the viscosity term. Log(MolWt[n]) is the log (base 10) of the hydrodynamic volume.

STEP 6Click the Viscosity Law tab to view the Viscosity Law plot which is also known as the Mark-Houwink plot. This plot illustrates the relationship between viscosity and molecular weight. The slope of the plot is alpha, and the y-intercept is K.

STEP 7Here is a comparison of the results for a polymer processed using the Universal calibration curve versus the Relative calibration curve developed in an earlier tip. Why is there a difference in the molecular weights?

Email me at neil_j_lander@waters.com with your answer!

It’s that easy!

Final Note

Intrinsic viscosity is the polymer’s contribution to the viscosity when it is in solution.