Contaminants m/z 113.996 127.9

Hello,We use Aquity UPLC coupled with a Q-TOF for metabonomics applications (scan 50 - 1000 m/z). LC eluents are water and methanol, both with 0.1% FA. We know that water-FA contains a main contaminant with 113.96 m/z and methanol-FA a contaminat with 127.9 m/z. Usually, these contaminants are constantly present in the baseline as shown in the Figure 1 of the pdf file attached. Recently, we observed that these contaminants (mainly the contaminant with 113.96 m/z) elute in fits and starts, forming a train of reiterated peaks that doesn't have any apparent repeatability in the retention times (Figure 2). This problem was observed for the first time with a HSS T3 column 100 mm + VanGuard pre-column, but even changing the column the problem still persists. After the preventive maintenance of the UPLC we observed a reduced number of peaks even if the problem wasn't completely fixed. Could the contaminants be due to TFA, that it is present in trace in the FA added to the eluents? Why contaminants elute as chromatographic peaks? Corrective actions?ThanksElia

Answers

  • Elia,

    I looked up the masses you are seeing in a table of common contaminants and adducts seen in mass spectrometry and could not identify these two masses with any certainty. In positive electrospray, it is unlikely you are seeing TFA contamination. This would be more easily seen in ES- mode. However, the good news is that you definitely see a reduction in these peaks after system cleaning. I was wondering what your cleaning procedures were? Perhaps you simply need to flush the system longer and with a variety of solvents. First, we recommend high quality (Optima Grade) solvents and additives if you can get them. I have also attached a thorough cleaning procedure that should remove contamination associated with the system. Do not allow any of these solutions to go into the mass spectrometer. Simply disconnect it. You may also want to clean the sample cone thoroughly to rule out MS system contamination.

    Finally, have you replaced both the guard column and analytical column? Do these peaks appear when both of these are replaced?

    Please keep us posted on your progress.

    Ken

  • Hello:

    It could also be mchanical and that the pump is delivering inconsistently causing the Formic Acid to elute in fits and starts.

    Could you send the primary and accumulator traces and the mobile phase conditions. Can you confirm that you are running isocratically and dialing in the required mixture. If so run with pre-mixed solvents and test to see what happens.

    Many TX

    Liz

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