By Noah on Friday, August 6, 2004 - 04:59 am:

Hi, everybody

Everytime when I run a blank or sample on LC/MS,ESI+, mobile phase (acetonitrile-water), I obtain m/z 102.3 Can any one tell me what is the cause of this peak?

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By Kostas Petritis on Friday, August 6, 2004 - 09:22 am:

Noah,

This is due to triethylamine (molecular weight of 101). Kind of difficult to get rid of it but still feasable.

Kostas

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By Noah on Monday, August 9, 2004 - 11:53 pm:

Thank you Kostas Petritis, but to my surprise is that I did not add triethylamine to mobile phase and blank. Can you please explain what might be the cause?

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By Kostas Petritis on Tuesday, August 10, 2004 - 01:53 pm:

Hi Noah,

It might be your column if ever has been used with triethylamine in the past or maybe someone used in the past a mobile phase with triethylamine and negative ionisation but as I said before it is kind of difficult to get rid of it.

Do you see the peak when 1) you infuse fresh water:methanol if not 2) do you see it when you infuse your mobile phase, if not 3) do you see it if you pump your mobile phase without the column if not 4) do you see it when you pump through the column?
If 1 is yes then your MS is polluted by that, in general I get rid of volatile pollutions by using the heated nebuliser with 50:50 water methanol overnight at 300-400 C.
If 1 is no and 2 is yes then your mobile phase is propably contaminated.
If 1-2 is no and 3 is yes maybe the pump still gives you some of the triethylamine propably due to previous use of it (kind of unlike though).
If 1-3 is no and 4 is yes then your column still leaks triethylamine, assuming that you have used a previous method that contained triethylamine with the same column.

Anyway all the above are assumptions, I hope something of the above will work for you.

Let us know if ever you track down the reason, it will might help someone in the future...

Kostas

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By Noah on Wednesday, August 11, 2004 - 04:00 am:

Thank you Kostas, I will come back to you.

Best regards
Noah

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By Noah on Thursday, August 19, 2004 - 04:24 am:

Hi, Kostas

I think my MS is polluted with triethylamine. I remember at one stage, a service technician messed up the ion source compartment with one of the buffers, of which I think one of them contained triethylamine.Leaving the nebuliser heated overnight at 300-500 is not gonna be possible for me, Nitrogen gas is going to be finished within some few hours. My MS is consuming 700 liters/hour. Is there any method that I can use to get rid of this? If I leave it, will it not affect my future results?

Thank you

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By Kostas Petritis on Wednesday, August 25, 2004 - 04:20 pm:

Hi Noah,

I am sorry to hear that a service technician used triethylamine by error. Actually I remembered of an article describing the problems you might have if you use triethylamine or if your MS is polluted with triethylamine. The reference is below and I have copy paste an interesting part that might be the answer in your problem (quite labor intensive unfortunately). Personally I faced the problem of triethylamine some year ago when I wanted to analyse ACC (1-amino cyclopropane-1-carboxylic acid MW=101) so even traces of triethylamine decrased the LOD of my analysis. Fortunately, by using MS/MS I was able to be more specific and deal with that problem.
The reference for that is: K. Petritis et al. Phytochemical Analysis 14, 2003, 347-351.

And here is a letter to the editor about triethylamine and the problems it causes if it is used with MS.

Rutters H, Mohring T, Rullkotter J, et al.
The persistent memory effect of triethylamine in the analysis of phospholipids by liquid chromatography/mass spectrometry
RAPID COMMUNICATIONS IN MASS SPECTROMETRY 14 (2): 122-123 2000

As the vacuum unit of the LCQ instrument is not designed for baking, other procedures had to be employed to remove the contaminant (TEA). Even several cleaning cycles of ESI source, heated capillary, API stack and the ion optics using various solvents and replacement of a number of mass spectrometer parts, tentatively identified as the most contaminated ones, did not significantly reduce the intensity of the TEA signal. Cleaning procedures recommended by the instrument manufacturer (Thermoquest, personal
communication) or other researchers working with TEA (DeJohn, personal communication), i.e. sonication with formic acid/acetonitrile (50:50 v/v) did not improve the instrument performance.
Finally, we disassembled the whole vacuum unit and all attached parts of the instrument, had all the metal pieces (ion optics, trap, vacuum manifold, etc.) cleaned by a mass spectrometer manufacturer (MassTech, Bremen, Germany) and replaced all Teflon, PEEK and other plastic components (including analyzer mount, tube lense and skimmer mount, all sealings, tubings, etc.). This ultimately removed the TEA contamination to a level below the detection limit. From this experience we conclude that TEA was strongly adsorbed on the surfaces of the vacuum manifold
and parts therein. Ionization may have occurred by proton transfer from solvent ions generated by the ESI process to desorbed TEA molecules.
Therefore, we strongly recommend refraining from the use of triethylamine in analyses using ion-trap LC/MS and considering alternative eluent modifiers if the instrument is ever to be used for the analysis of low molecular weight substances in positive ion mode.

Hope the above helps!

Regards,

Kostas