Sudden drop of MS signal

[yangz00g]

Bad luck recently.

Running a LC-MS/MS methods for some nerve agents, LC is water 2795, MS is Micromass Quattro LC, with Z-spray ESI. Everything worked fine last week, all of a sudden, the sensitivity droped this week to about 10% of last week's. No seting has been changed.

Cleaned the coins, signal went up a little bit, still only portion of last week's, and began to drop after a few injections. No time to clean the source, is really a dirty source can have such big effects? I doubt. Anyone has similar experience? Thanks in advance.

[MIB_EO]

"really a dirty source can have such big effects?"

Yes absolutely it can.

However before you do so I'd check your spray and capillary. A dirty or partially block probe is often a cause. Check with fresh sample too, another frequent cause of poor sensitivity. Also check your gas supply and pressures.

[alpesh]

we are using API instruments. we have never faced problem mentioned by you. dirty source is always been a problem for sensitivity drop but not to the extent said by you. source cleaning will always get back sensitivity. there might be something wrong with either LC part or MS part
alpesh

[yangz00g]

MIB-EO and Alpesh, thanks

Everything we can check was checked and compared to previously saved settings, nothing abnormal. We began to think it's problem of the HILIC column (HILIC!), the bleeding partices from the propably aged column might cause the problem. A new cloumn was in palce, coins cleaned, capillary checked ( I still don't believe a dirty source can cause such a sharp drop, so we did not clean the source, in addition , we don't have time), sensitivity got up to the level we had right after a coin cleansing yesterday, and seemed to drop again after a few injections (still running. BTW, we use new mobile phase, clean matrix at this point. Any inputs? Could be some electronic parts malfucntioned, but the reading is OK?

[Patrik Appelblad]

Could it be related to any components in the mobile phase?
Have you a new source of buffer salts?

At negative mode I've seen similar effects among different sources of ammonium acetate at neutral pH.

[sassman]

You said that you checked the capillary. How did you do that? Are you getting a good spray? It should be smooth with no sputtering.