Hello Everyone
Currently, I use 1260 Infinity II GPC/SEC MDS (with RI detector and Viscometer) for molecular weight determination.
Some of my sample have weird RI peak. And, this affects calculated Mn and Mw.
Apart from positive sharp RI peak, I have negative and fluctuate RI peak as attached figures.
Anyone know how to fix this problem ? I do not know it is because my sample / detector / or anything else
Hi Phuthiphong,
You mention “strange” RI peaks. Based on a screenshot of your first sample shown (see below), it appears that the yellow highlighted part of your RI signal is the solvent peak. Since your sample peak is very close to the solvent peak and might even interfere with it, I can only recommend you to switch to a column set with smaller particle sizes/pores or add another column to your column set (however, I assume you are already using three columns if you are measuring at 1 ml/min).
The negative RI peak from your sample pyk5 is due to a negative dn/dc value. The signal intensity (SI) in RI detectors (concentration detector) is based on SI = c * dn/dc. For some polymer/solvent pairs, the dn/dc is negative. Sample ss02 is showing a differential peak indicating the eluting sample component has a partial negative dn/dc.
Another hint: The viscometry trace is showing a pressure pulse on each injection and thus the injection system should be serviced to avoid this behaviour.
Best regards!
