We analyse oligonucletide using Ion-pair reversed phase chromatography. The mobile phase A is composed of triethylamine (TEA), hexafluoroisopropanol (HFIP), water. And the mobile phase B is the mixture of methanol and acetonitrile. The ghost peak has no specific UV absorption, so this is not derived from sample. This peak does not always appear. And this ghost peak does not show Gaussian distribution and is jagged. We think that this comes from TEA, but we don't have good resolution for this. Do you know the reason why the mobile phase that contains HFIP-TEA produce a big ghost peak?
From your description, the TEA is used as the free base.
1) This might damage a bonded-phase column.
2) For ion pairing, the TEA needs to be protonated; usually one uses an acid that acts as a buffer e.g. formate, acetate, bicarbonate; the bicarbonate is the easiest to evaporate.
3) When the TEA is not buffered, the solution you inject is likely to alter the ionic composition of the mobile phase, causing one or more "system peaks". There is some literature on system peaks, partly because they have been used to determine analytes that have no detector response. In your case a system peak might be due to an impurity or degradation product of a mobile phase component.
The suggestions made are possible causes. However, their is another well documented and likely explanation too. HFIP is not recommended for use with a lot of HPLC systems. Please see linked article for more info.
- "An Often Ignored HPLC & LC/MS Contamination Source. Did you check your Vacuum Degasser?"; https://hplctips.blogspot.com/2015/08/an-often-ignored-hplc-lcms.html
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