sudden drop in baseline

[jzt]

I would like to follow up on a question I posted more than a year ago, see the link to the old post which contains chromatograms: http://www.sepsci.com/chromforum/viewtopic.php?t=1591

When we encountered this issue, we were under very tight timeline to get the method done. So we switched the column from Synergi Polar-RP to ODS AQ. The baseline issue was resolved even though sample diluent, mobile phases and gradient remained the same. We never had time to go back and figure out what was going on.

A few months ago I was developing a new impurity method for a new compound. During the column screening stage, I saw the same baseline issue again with the Synergi Polar-RP but not with other Synergi columns. The problem was more pronounced at low wavelengths (210 or 220 nm), but not observed at 250 nm. I called the column vendor and was told that such baseline was known as the “shark fin baselineâ€

[haibinwan]

Your mobile phase is of quite low pH. It nears the lower pH limit of most silical based columns. The Zorbax SB columns (stable bond) can go down to pH 1. That is why it is stable for your case.

[zoom]

I've seen the same thing with the Synergi Polar-RP column. This column bleeds more than other phenyl columns because it has an ether linkage on its hydrocarbon connector.

The Polar-RP does not seem to be very robust. The one that I had died after only a few months.

[PJ8]

Has anyone else seen sharkfin like baseline problems on Luna phenyl hexyl columns? Is this a problem with individual column batches or just a problem with phenyl phases that happens after 'a while'?

How did the Luna PhHex fair on your colleagues test jzt?

[jzt]

PJ8,

sorry for the late reply. I didn't have time to check the forum recently. I asked my colleague, he said the phenyl hexyl is not so good.

[PJ8]

Thanks a lot JZT.

[Bryan Evans]

Hi JZT -

Have you tried our Unison UK-Phenyl column?
It also will give very low column bleed under acidic conditions.
Our polyfunctional ligand bonding and polymeric endcapping
are what make the Unison series so durable under acidic
environments:

http://www.silvertonesciences.com/modul ... TI118E.pdf