Chromatography Forum

Hi All,

In February we bought in 2 new Waters Triple Quad XRs, coupled to their premier UPLC system. Ever since we got them we have had nothing but problems with some form of contamination that's resulting in a very high baseline completely obscuring our peaks. I've tried everything I can think of to try and find the source of the contamination for good but so far have had no luck. We have been successful in getting rid of it once or twice, but it keeps coming back.

Here's all the information we have:

• For some reason this happens exclusively on the XRs, we’ve not had any contamination issues on any of our other Classic, I-class or absolute systems
• Contamination comes in the form of a high baseline that sits at around 95% and completely obscures any actual analytical peaks
• Contamination is not consistent across all analytes, just some, typically higher Mass (around 600-800), however as contamination gets worse, more analytes are affected.
• As well as high baseline, Contamination has also been discovered for actual analytical peaks, this is seen by doing a 0 ul injection of a freshly prepared solvent blank that has been prepared nowhere near any of the analytes
• Doing an MS radar scan from a mass range of 100-800 on a contaminated system shows a lot of very intense MS peaks, (e9) starting at around a few hundred
• Mobile phases, seal washes, needle washes have been prepared fresh, double gloved for analysis and still resulted in contamination
• Acid and base flush procedures seems to work on one system but not the other, this was the case both when the contamination first appeared and when it reappeared recently.
• Its highly suspected the contamination is in the LC over the MS, but this isnt certain.

any help or advice would be greatly appreciated.
Thanks

I would an injection with the gradient run twice in same method. Is second gradient background same as the first. Also solvents may be checked by direkt infusion and product ion scans for your target molecules.

Have you tried isolating whether the contaminant originates from the LC or the MS by bypassing the LC entirely and doing a direct infusion of the mobile phase into the MS source? Also, checking the system oil pumps or the nitrogen gas supply line might help rule out unexpected background sources.

Have you tried different types of glassware? Certain vendors have been a problem for very sensitive detectors. The one starting w/ S and ending in chott is one example...