Chromatography Forum

Lately, I've noticed the disappearance of the peaks for a high MW compound that is normally present in our sample matrices (C20-ish). I tried increasing the oven temp at the end of the run, holding the run longer at the final temp, increasing the injector port temp (in case it was getting stuck in the inlet), and it seems like it is getting stuck somewhere. Then I noticed that right around where the compound should be eluting, the baseline is drifting upward about 2pA.

Any thoughts on what is happening?

Also, when it comes to sustaining chromatographic integrity regarding column contamination, what is the best method of recurring maintenance: solvent wash or baking?

Thanks, guys!

Peaks often disappear due to contamination in the inlet so first clean your inlet and replace the liner. If that doesn't restore the peak(s), cut off one meter from the inlet end of the column. That is where sample crud condenses irreversibly changing the column activity.

Also, when it comes to sustaining chromatographic integrity regarding column contamination, what is the best method of recurring maintenance: solvent wash or baking?

The best practices for column maintenance are to change inlet liners often to minimize crud getting onto the column. Cutting on-meter increments from the front of the column is the second step. Flushing the column with solvents is the last resort and may or may not be effective.

@skunked_once: Thank you for the response! The inlet was cleaned earlier this week and the liner was replaced, too, so that isn't where the problem lies. I haven't yet cut the column, so I think that will be the next step, then followed by a solvent rinse if the problem isn't solved.

Is it possible that column bleed can cover up smaller peaks?

If this is a matrix peak (i.e. not a target analyte) then why are you worried that it has gone away ? And are you sure that it is still present in the samples ? How do the rest of the peaks look ?

In my experience solvent rinsing can turn a really bad column into a barely acceptable one, or an acceptable one into a piece of junk. Do it only as a last resort.

"Baking out" has probably damaged more columns than it has saved - stationary phases suffer at high temperatures for long periods, especially if the carrier gas is not really really clean. If you do try it, reverse the column, put the detector end into the inlet so that the heavy crud gets pushed out of the inlet end rather than deeper into the column.

Chopping off the first metre can do no harm.

Peter

I would pull the brand-new column spare out of the drawer and try that. If better, use it and order new spare. If same, return new column to the drawer and keep troubleshooting.