Chromatography Forum

Dear collegues,

I'm using a GPC column with a pH 7,0 mobile phase (0,4M phosphate buffer) to detect and assay hyaluronic acid (MW:10xE6 D) in pharmaceutical products. The method I validated had plate count of 2000. Plate count values are reccomended higher than 4000, but I think it is not possible to increase plate count with this tecnique, as retention is only physical.
Am I wrong?
Thanks in advance!
A.M.

Assuming that you are talking about different plate counts with the same column, one certainly can change it via a change in macro molecule shape, via matrix (solvent) influence. On top of this, there is no such thing as pure size exclusion, so chances exist that one can change peak shape via changing interactions with the stationary phase as well.

In addition to Hans' comments, I'll point out that, to be meaningful, the plate count on a GPC column should be measured with a marker of clearly defined molecular weight. If your analyte has a distribution of molecular weights, what you will see is a broad peak which is essentially the superposition of all the narrower peaks for the individual species in that distribution. Trying to compute a plate count from this type of peak is essentially meaningless