I need your comments on the optimal conditions for measuring underivatized N-glycans in ESI-MS in negative mode?

Normally in GC-MS results will be in retention time vs peak area. Has anyone tried to get the retention index from the raw data of the chromatogram using any software?

The rules for authorship are often vague or non-existent. How much input from the person performing mass spectrometry analysis do you feel is required to warrant inclusion as an author? For example, does a paid service (in-gel digestion of submitted gel bands) or technical assistance justify authorship? Or, is data production usually accompanied by analysis? If so, what depth of analysis? I am especially interested in comments from members of core facilities with regard to how much work they perform to be (or not be) an author on a collaborators manuscript.

We need an accurate mass calibration solution which covers the whole mass range without contaminationg our system too much. Actually we use a mix containing Ultramark 1621 and several other compounds of lower masses. We don't like to use sodium salt clusters, since it causes many sodium aducts even after cleaning. We were also not really satisfied with PEGs as well as CsI.Therfore we are looking for about 2-3 compounds in the mass range of 2000 to 4000 whitch are avialabel in a good qualty, give a good signal in positve and negative mode, are cheap, and do not contaminate our system too much.

Does anyone know of a LC-MS/MS or LC-MS method for the analysis of pregnenolone 16 alpha carbonitrile in plasma samples?

They are a complex of basic, acidic and neutral. I need the range to be from 0.5 to 50 ug/ml to include the lethal dose but I am getting up to 25ug/ml only for most of them. With higher concentrations , I have a quadratic curve. I am using a C18 column (150*2.0 mm, 5u) with 10 mM Ammonium acetate and ACN with gradient system.

We are using an LC-MS iontrap with ESI.

in mass spectrometry, we used negative ion mode deprotonated in ESI. What does deprotonation mean?

I have been working for a method development for perfluorocarboxylic acids (10 compounds) using LC/MS/MS (Agilent 6410). I started with MS parameter optimization by injecting individual compound (in methanol) directly into the mass spec and monitoring transition ions which I obtained from literature. My understanding is that, I would maximize the precursor ion in MS1 by changing fragmentor voltage (often called cone voltage), and then maximize the product ion in MS2 by changing collision energy.

However, for the compounds of interest, I am observing both precursor and product ions in the MS1 scan in comparable abundance. That also means, the product ion is maximized in MS2 for zero or very small collision energy. If I apply higher collision (> 3ev) energy, the product ions are decreasing.

I understand the collision and fragmentor voltage are instrument specific. The literature I am looking into has used a range 8-20 ev collision energy.

I would really appreciate any input in addressing the following concerns:

1. Would my method be valid if I observe both the ions in MS1 and report zero collision energy for product ion?

 If not,

2. What can I do to remedy this situation?

3. I have seen a paper using pseudo MRM for similar compounds where they monitored same ion in MS1 and MS2. Can I use similar approach?

Thanks in advance.