LC-MS Problem, Please help

[dreamer_25m]

When I go to 100% ACN (say 5 to 100% ACN in 15 mints and keep 100% ACN for 5 minutes, in a ghradient) in a Trap I always see two predominat ions, 256 and 282 (ESI, +). I normally use SB C8 or C 18 column.
The trap we are using is Agilent SL.
Its is very problematic, specially if the compound of interest elutes out at 100% ACN because these two peaks (282, 256) are so huge that they almost mask other ions.
I have tried cleaning procedure elaborately and it didnt help. The peak is not coming from LC as it is present when I use syringe pump for direct infusion as well.
The agilent engineer is saying it is true universally. Everyone sees those ions when you go go to 100% ACN and keep the gradient for few minutes. Somehow I dont agree with that and I would really really appreciate the readers observation in this regard.

[Ericz]

Peak 282 is said to be typical from plasticizer. I guess 256 is associated with that, too, although the difference is 26 which I have no idea about (C2H2???). Can anybody have more ideas?

[MG]

I have a list of "Common LC/MSD contaminants" from Agilent, dated from 12/2000. According to the list, 256 and 284 come from nylon filters (sometimes used to filter mobile phases). Not sure about 282.

[Basil]

Hi MG,

I also have an MSD Trap from Agilent, and it would be very usefull to have the list of common LC/MSD contaminants.

Did you downloaded from the agilent web page ?.

Or you could send to us by e-mail ?

Thanks

[dreamer_25m]

Thanks for all the replies. Any of you see these peaks when you go to 100% ACN and keep it for few mints.
There was a discussion before and some one attributed 282 is the protonated oleic acid amide(281+H+)
The common LCMS contaminant table can be obtained from Agilent
Thanks again.

[jan]

Hi, MG,

I am very interested to see the list of "Common LC/MSD contaminants" you mentioned. Is that possible for you to post this list? Thank you very much.

Jan

[MG]

I don't remember where I got the list. It is a photocopy, probably dating from when we had an LC/MSD. I couldn't find it on the web either. I imagine Agilent would probably make it available to their customers who use their LC/MS equipment. I don't really want to post the whole list here, mainly because I don't have time to type it all in, and also because I suppose there could by copyright issues. Sorry.

In the absence of that, here's a link you may find useful, that gives several references on contaminant ions.

http://www.xasa.com/grupos/en/sci/artic ... .mass-spec

I already had the U. of Southampton table and the JASMS article printed. Neither one mention 256, but the JASMS article attributes m/z 282 to "plasticizer in polyethylene".