Mass drift in Ion trap

[Atinuch40]

Dear all

I am trying to analyse urinary F2-Isoprostane (m/z 353 to 193)
by ESI-Ion trap XCT with negative ionisation .

Mobile phase is 5 mM ammonium acetate and MeOH:ACN. I prepare sample by SPE and inject sample during 7-9 min into MS

I have good LOQ and good mass spectra 6 months ago but now
I am getting poor sensitivity and I have a problem about mass drift
(drift from 353) when I inject spiked standard at low concentration about 12 ng/ml so it get low or no fragmentation.

I tune MS by tuning mixer and analyte but mass still drift.

Does anyone have any suggestions?

[MIB_EO]

More details please.
Over what time scale is your mass drift?

Does the drift happen over the course of a run? or a day? or from one day to the next? or is it that the mass is no longer the same as it was six months ago?

How big is the magnitude of drift over what time? is it always in the same direction?

Is the resolution / sensitivity effected?

Have you checked the calibration? How current is it? How is the temperature stability in your lab? Have you experianced power supply issues recently? are you on a UPS?

Temperature is the most common cause of change in mass position.
If the mass is noticeable drifitng over an hour you probably have an instrument fault (breakdown in the detector or a failing power supply neither of which is user servicable).

[Atinuch40]

In the first injection everything is OK, it always drift after 2-3 injection.
We set the mass range at 353 +/- 0.5. So if mass is drifted over this range (>+/- 0.5).

After work I tuned MS by tuning mixer and I found that the mass drift from the normal mass of tuning mixer so I have to adjust mass and tuned by manual tune.
After that I come back in the next day it still drift so I have to tune it again.

I don’t think the temperature is the cause of mass drift because the room is well temperature control and we have UPS.

Another problem I recently found that in spiked sample, m/z 353 always spilt into 2 mass 352.1 and 353, m/z 353 still fragment but not thing happen with m/z 352.1 so fragmentation is not complete and I have low peak area of 193.
Is it the matrix effect?. But it is the same urine as six month ago.

I need to show you our mass spectra but I don’t know how to do.

Last week I cleaned capillary and we found that the top of capillary had a tiny scratch on the ionization source side. Could this be the cause of the problem?

If the mass drift cause from an instrument how can I do?

I quite new with LC/MSMS, I'm so sorry if my answer make you confuse :
( Thank you

[Atinuch40]

In the first injection everything is OK, it always drift after 2-3 injection.
We set the mass range at 353 +/- 0.5. So if mass is drifted over this range (>+/- 0.5).

After work I tuned MS by tuning mixer and I found that the mass drift from the normal mass of tuning mixer so I have to adjust mass and tuned by manual tune.
After that I come back in the next day it still drift so I have to tune it again.

I don’t think the temperature is the cause of mass drift because the room is well temperature control and we have UPS.

Another problem I recently found that in spiked sample, m/z 353 always spilt into 2 mass 352.1 and 353, m/z 353 still fragment but not thing happen with m/z 352.1 so fragmentation is not complete and I have low peak area of 193.
Is it the matrix effect?. But it is the same urine as six month ago.

I need to show you our mass spectra but I don’t know how to do.

Last week I cleaned capillary and we found that the top of capillary had a tiny scratch on the ionization source side. Could this be the cause of the problem?

If the mass drift cause from an instrument how can I do?

I quite new with LC/MSMS, I'm so sorry if my answer make you confuse :
( Thank you

[Atinuch40]

In the first injection everything is OK, it always drift after 2-3 injection.
We set the mass range at 353 +/- 0.5. So if mass is drifted over this range (>+/- 0.5).

After work I tuned MS by tuning mixer and I found that the mass drift from the normal mass of tuning mixer so I have to adjust mass and tuned by manual tune.
After that I come back in the next day it still drift so I have to tune it again.

I don’t think the temperature is the cause of mass drift because the room is well temperature control and we have UPS.

Another problem I recently found that in spiked sample, m/z 353 always spilt into 2 mass 352.1 and 353, m/z 353 still fragment but not thing happen with m/z 352.1 so fragmentation is not complete and I have low peak area of 193.
Is it the matrix effect?. But it is the same urine as six month ago.

I need to show you our mass spectra but I don’t know how to do.

Last week I cleaned capillary and we found that the top of capillary had a tiny scratch on the ionization source side. Could this be the cause of the problem?

If the mass drift cause from an instrument how can I do?

I quite new with LC/MSMS, I'm so sorry if my answer make you confuse :
( Thank you

[MIB_EO]

So If I've understood you: on your first injection you see a peak at 353. On you second injection of the same sample you don't, but if you re-tune you can ?

Have you tried other samples? Try some other standards. Does the same thing still happen? If it does then you probably need to contact the manufacturer see below.

If it doesn't then it is a sample issue. samples do degrade over time.


"capillary had a tiny scratch" This may cause sensitivity problems it cannot have anything to do with mass drift as the mass is analysed later in the ion path.

"If the mass drift cause from an instrument"
This does sound like an instrument problem to me. You should contact the instrument manufacturer's technical support department as there is unlikely to be anything you can do without service support. Try their webpage for contact details.