By Leil on Saturday, February 28, 2004 - 02:41 am:
I'm seing a m/z corresponding to previous MS analysis in all the analyses I'm performing further. Attempts to infuse several time the solvent of the sample didn't help. Are there recommended way to get rid of such a mass?
By Anonymous on Saturday, February 28, 2004 - 07:41 am:
MS? LC/MS? Infuse how?
By Anonymous on Monday, March 1, 2004 - 01:04 am:
To infuse ACN/H2O 50/50 or ACN/H2O 90/10.
By MG on Monday, March 1, 2004 - 06:22 am:
If this is infusion only with syringe pump (no LC), then wash your syringe 5 or 10 times with solvent. With your tubing disconnected from the ion source, flush an entire syringe volume of solvent through the tubing into a waste container. Reconnect your tubing and let the syringe pump run for a little while, then see if the ions are still there. Some compounds used as mass calibrants, such as PPG or Ultramark, are notorius for memory effects. For those, it's best to reserve a separate syringe and tubing for their use.
By Leil on Monday, March 1, 2004 - 12:00 pm:
The mass observed correspond to the compound used to fine tune the MS detector. At the end of tuning procedure, the seringe was washed with several time with MeOH/H2O 50/50. The compound is soluble in methanol. Although pumping several times entire seringe of MeOH/H2O 50/50, that mass can still be observed. The tuning procedure and pumping with MeOH/H2O, were performed with a flow of the mobile phase. In further step, when the system was used for LC/MS for another application (other compounds), the TIC chromatogram showed a peak with m/z corresponding to that compound.
By MG on Monday, March 1, 2004 - 03:03 pm:
You can also try cleaning your ion source and see if that helps.
When you say you saw a peak with m/z corresponding to your tuning compound, do you mean that this was a chromatographic peak, or that you see the tuning mass as constant background?
By Leil on Wednesday, March 3, 2004 - 05:01 am:
A distinct peak is really observed in the TIC chromatogram with m/z of the tuning copmound. By the way I way no idea on how to clean the ion source.
By MG on Wednesday, March 3, 2004 - 08:51 am:
If there's a distinct chromatographic peak, that's a different problem. Something with that mass has contaminated your autosampler, column or mobile phases. If it's a gradient analysis, running the gradient with no injection will help isolate the problem.
Call your MS manufacturer's tech support number, and someone will probably tell you how to clean the front side of your ion source. Even if it's not related to this problem, it will be useful knowledge to have. Eventually, the cleaning will be needed.