By Philip Lowden on Tuesday, July 27, 2004 - 03:29 pm:

I am getting a large series of nasty contaminant peaks in LCMS, separated by 14 mass units, covering a range from ~100 to ~600, examples include 255, 269, etc. There are also smaller peaks at 2 and 4 mass units less than the main series. This is with a water/acetonitrile mix (both fresh HPLC Gradient Grade from Fisher Scientific) and a (brand new) microbore C18 column. Any ideas what this could be and how to get rid of it? Thanks.

-------------------------------------------------------------------------------------------------------
By tom jupille on Wednesday, July 28, 2004 - 09:17 am:

Residual detergent on your glassware?

-------------------------------------------------------------------------------------------------------
By nitin karalkar on Thursday, July 29, 2004 - 01:55 am:

If you are getting the difference of 14 then thers are chances that you are getting the adducts of ammonia of molucular wt 14. Check your buffers and athe contant of buffersin mobile phase

-------------------------------------------------------------------------------------------------------
By michelle on Friday, July 30, 2004 - 03:57 pm:

Philip,
If you used the ESI- model, the 255, 269, 283 might be the fatty acid- , 14 is -CH2-. 283- is the stearic acid anion. Less 2 or 4 means corresponding unsaturate C-chain.
But I am not sure for your less information.
Michelle

-------------------------------------------------------------------------------------------------------
By Grant H on Tuesday, August 24, 2004 - 12:23 pm:

Have you resolved this issue? If you also have predominate peaks at 325, 311, and 297 it could be Micro detergent from glassware as mentioned earlier, when you are in ESI- mode. It would be the loss of CH2 in the case of Micro. This is something we have seen and have since kept all LC/MS glassware seperate from the regular washed glassware and the problem has gone away.

Grant