Persistant ghost peak????

Sue1975

<p> I wonder if someone could help us.  We have had a few pump issues with our UPLC and the last time an engineer came he replaced the whole torpedo unit on primary pump B.  He left the system in perfect working order (many thanks!).  Unfortunately since then, we now have a strange peak in our chromatograms.  It is not contamination in any of our solutions/mobile phases/sample solvent.  The method is not heavily buffered, we use a gradient with ACN & 20mM potassium hexafluorophosphate pH 2.5.  The sample solvent is a 50:50 mix of the mobile phase.  We have performed wash after wash over several days, including the routine cleaning from sheet 715001908 REV. A.  We have tried new columns, changed the sample syringe and needle and still it remains.  Does anyone have any ideas of what it could be?  Could it be something from the change of torpedo?  Any help gratefully received.</p>

WesleyCrozier

Our lab had an issue similar to this one and we discovered it was contamination in our water.  Even HPLC grade water will have miniscule amounts of contaminant that stick, amplify and then elute at a specific point in the gradient.  If the peak(s) is consistantly the same area count even after repeat injections of entirely different compounds it's a good indication the contamination is from the mobile phase.  I doubt it has anything to do with the pumps being changed, as any contamination there would decrease in intensity after such rigorous washing.  It sounds like perhaps something else happened around that time.

lconnor1

I have attached a pdf document that I found very helpful. It outlines the many possible sources of contamination in RP gradient chromatography. You can eliminate them one by one starting with the most obvious.

Another good source to look at is LCGC Online. An article I read recently was titled:

Ghost Peak Investigation in a Reversed-Phase Gradient LC System

May 1, 2011 By: Silvia Sadikin, Dee Dee Zhang, Roger Inloes, Sanjeev Redkar, John W. Dolan LCGC North America

Follow this link: http://chromatographyonline.findanalytichem.com/lcgc/article/articleDetail.jsp?id=725248

Good luck

Zach_Giles_GSK

My old lab saw a similiar issue and it was in the formic acid we were adding.  I didn't see you mention it but I thought I'd throw it out there, as I think it could be a mobile phase issue as well.  Our formic was being delivered in plastic bottles, and when we switched to formic in glass bottles the problem went away.  Also, you can try changing the sample loop and/or the valve on the sample manager.  I wouldn't expect anything from changing the torpedo since the torpedo only controls the piston, and doesn't actually touch solvent...unless some oil or something got on the piston during the install.

WesleyCrozier

We have very prominant ghost peaks when running a gradient with Formic acid.  It happens to be in plastic bottles, so that may be the issue.  Could you give us your source for formic acid in glass bottles?

Zach_Giles_GSK

We got it from EMD cat# 11670-1.  It's insanely expensive (~$800), but it eliminated our ghost peak.