removing ion-pair reagent contamination
We have recently completed the analysis of a set of samples using ion-pair chromatography. Although I was quite pleased with the results, the mobile phases we used, (nonafluoro pentanoic acid on one instrument, and pentafluoroheptanoic acid on another instrument - both are Aquity UPLCs), are proving extremely difficult to get rid of; both instruments show quite clear IPR parent ion contamination even after exhaustive flushing sequences. We've tried all the recommended flushing mixes (acid, base, strong solvent, weak solvent) and have also changed a number of different filters (solvent frits, in-line filters, mixer) and tubing (of course there is no column). In 15 years of working with LCs I have really never seen a contamination issue quite like this before; I was wondering if anybody had experienced a similar problem and could perhaps advise us on how to proceed. An online chromatography forum answer has just suggested that the degasser could be the source of the problem; is this a straightforward / cheap component to change over?