how to explain the signal from runing of empty MS

[meillid]

when I just run empty MS (no infusion, no LC), I detect pretty strong signal of d0 NITROSAMINE which I run earlier even after 24hr bake out the instrument. Can the instrument be contaminated so much? what else to explain this? Did anyone ever run a empty MS? did you see any signals from this kind of experiment? Thanks a lot.

[Kostas Petritis]

It sounds like contamination...

Unless nitrosamine is very sticky (such as triethylamine) something wrong has been done. I do not know what kind of instrument are you using, but if after baking all the front part (i.e. orrifice etc) you still see the contamination, maybe is time for some tech support...

[meillid]

Kostas, I am using API2000. Thanks.

[Kostas Petritis]

Emily,

I read your previous messages and maybe the reason of your problems might be that "contamination". For example, heavily contaminated instruments, sometimes, they show only the contaminated ions, whatever you infuse. Have you tried to infuse something else (i.e. calibrant ions or some other compound than nitrosime). Do you see these ions?

If you still see only the contamination ions only, then maybe even when you are infusing nitrosime d8, you see only the contamination ions (i.e. nitrosamine d0). Have you tried to infuse your d8 in another mass spectrometer?

As for cleaning, unless you are a very experienced mass spectrometer, I wouldn't recommend to go any further than the Q0. In order to clen it (the Q0), you must vent your instrument down anyways, in the appropriate way (again I do not know your level of expertise).

If even after you have cleaned the Q0 the contamination is still there, I would call tech support, as probably the contamination is even furhter in the instrument.

[james little]

I have a Quattro Micro. After infusing for tuning at higher levels, I often see the compound in the background, but usually only when the LC eluent is being introduced or blank solvent added.

I always try to infuse as little as possible to tune, but to get the lowest detection limits for a compound, have to clean the sampling cone before getting the lowest detection limits..

[meillid]

I had tried to eliminate the possible contamination by baking the instrument for 24hr. It is good suggestion to infusion caliberate compound to further test the instrument. Thanks a lot.

[JA]

Is "baking out" a cleaning procedure defined for the maintenance of your instrument? I don't have any experience with Sciex equipment. We use Waters ZQ's (want triple quad ) and as James mentioned, contaminants can be seen when pushing some eluent into the source. Infact when flow stops all ions seem to disappear..

I've anecdotal evidence (at least) that our probes have been contaminated, even blocked, from prolonged heating without adequate cleaning. This is especially true after infusions. For the ZQ, a lot of parts in the source, ion guide and even analyser can be cleaned by sonication in methanol. Occasionally some formic acid is added. If this doesn't do the job on the source components and we're still not happy, things get replaced.

Anyway, I was concerned that this bake out could actually lead to deposition of unwanted material.

[Rafael Chust]

In theory, baking is done with the system turned off (read, source and chromatograph off) and vacuum on.

The idea is to vaporize any contaminant remaining in the system... but, if the contaminant has a high boiling point or is somewhat greasy, then baking is not good enough - "mechanical" cleaning (meaning "house-keeping" sort of cleaning) is required.

Also, if you bake your system at low temp (emaning under 250ºC), it is a waste of time...

I had a funny contaminant in my early days of GC-MS - it was oil from an oil-less turbo pump flowing back to the source...