Chromatography Forum

ESI POS mode,

M+1 254.1 and fragments, 236, 218, 206, 188, all of fragment have equal intensity.

high resolution might indicates its formula to be C12H16NO5.

ESI POS mode,

M+1 254.1 and fragments, 236, 218, 206, 188, all of fragment have equal intensity.

high resolution might indicates its formula to be C12H16NO5.

ESI POS mode,

M+1 254.1 and fragments, 236, 218, 206, 188, all of fragment have equal intensity.

Maybe one of these? http://www.chemspider.com/Search.aspx?q ... 7d5ca435a0

Generally it helps to know as much as possible about the background of the sample you are analyzing.... (e.g. pharma-, enviromental-type, etc..)

From the fragments above you have loss of 2 H2O and loss of CH2O from your molecule (and that you should be able to confirm since you have access to accurate mass capabilities..).

Good luck.

Do you have any other indication of chemical characteristics? If you are separating by LC do you have any information about the compund from the location in the chromatogram?

What mass resolution is your instrument and how good is the mass accuracy (or another way - are there other fomulae that should be considered)? Just because you can get the instrument to print out four places after the decimal, there are instrumental issues that may limit the value of those numbers.

But most helpful is history of the sample. I've spend many hours the past several weeks trying to determine what several related compunds are in a mixture - and it would have been almost impossible without having a lot of information about the sample.

thanks for your help.
I wonder what kinds of function groups can loss water and fomaldehyde.
I assume should hydroxyl group and aldehyde group. any other thought?

Do you have any other indication of chemical characteristics? If you are separating by LC do you have any information about the compund from the location in the chromatogram?

What mass resolution is your instrument and how good is the mass accuracy (or another way - are there other fomulae that should be considered)? Just because you can get the instrument to print out four places after the decimal, there are instrumental issues that may limit the value of those numbers.

But most helpful is history of the sample. I've spend many hours the past several weeks trying to determine what several related compunds are in a mixture - and it would have been almost impossible without having a lot of information about the sample.

I guess water should be non-primary hydroxyl group and formaldehyde is primary hydroxyl group.

Do you have any other indication of chemical characteristics? If you are separating by LC do you have any information about the compund from the location in the chromatogram?

What mass resolution is your instrument and how good is the mass accuracy (or another way - are there other fomulae that should be considered)? Just because you can get the instrument to print out four places after the decimal, there are instrumental issues that may limit the value of those numbers.

But most helpful is history of the sample. I've spend many hours the past several weeks trying to determine what several related compunds are in a mixture - and it would have been almost impossible without having a lot of information about the sample.

Look at the fragmentation of alcohols. http://www.chemistry.ccsu.edu/glagovich ... index.html They often lose water by elimination, giving a neutral loss of 18. Would an aldehyde give rise to loss of formaldehyde? If you could get it to be protonated, maybe.

As I look at the loss of water, any abundance at 272 or 290? And do you have water in your solvent? What is your solvent by the way? Seeing the loss 254 to 236 (18 ) and 236 to 218 (18 again) I am wary of M+H+H2O. (I work largely with GC-MS but ESI is a chemical ionization type technique.)

Is this infusion or LC. The next question is: Do we know that these are all from the same compound. m/z 206 seems to break a pattern of losses of 18, but 188 is a loss of 18 from 206.

Where I am headed is: Perhaps you have a molecule formula C12H12NO3 and a mass of 218 and a second compound with mass 188.

And, if the instrument gave you an "accurate mass of " 254.1, you could have anything in the range from mass 254.05 to 254.15, and a bit more depending on the stability of your mass measurement. Examination of m+1, m+2, etc. might help, but will be confounded by the presence of the protonated molecular ion.

Without further information about the sample, an attempt to examine the mass spectral data will only lead to speculation and more questions.

[quote="jiang295"]I guess water should be non-primary hydroxyl group and formaldehyde is primary hydroxyl group.




Loss of CH2O might be from a CH2OH group present in your molecule. Loss of water might be from a OH (or more in your case).

LC-MS is not so powerful if you know absolutely nothing about your sample. Which LC-MS are you using? Q-TOF, iontrap?

thanks a lot for your detailed explanation.
sure, I want to isolate this compound for NMR.
my run is from lc.
I never see M+H+H2O in my esi.
what kind of compound will form this adduct?

Look at the fragmentation of alcohols. http://www.chemistry.ccsu.edu/glagovich ... index.html They often lose water by elimination, giving a neutral loss of 18. Would an aldehyde give rise to loss of formaldehyde? If you could get it to be protonated, maybe.

As I look at the loss of water, any abundance at 272 or 290? And do you have water in your solvent? What is your solvent by the way? Seeing the loss 254 to 236 (18 ) and 236 to 218 (18 again) I am wary of M+H+H2O. (I work largely with GC-MS but ESI is a chemical ionization type technique.)

Is this infusion or LC. The next question is: Do we know that these are all from the same compound. m/z 206 seems to break a pattern of losses of 18, but 188 is a loss of 18 from 206.

Where I am headed is: Perhaps you have a molecule formula C12H12NO3 and a mass of 218 and a second compound with mass 188.

And, if the instrument gave you an "accurate mass of " 254.1, you could have anything in the range from mass 254.05 to 254.15, and a bit more depending on the stability of your mass measurement. Examination of m+1, m+2, etc. might help, but will be confounded by the presence of the protonated molecular ion.

Without further information about the sample, an attempt to examine the mass spectral data will only lead to speculation and more questions.

thanks,

i am using waters qtof.

I guess water should be non-primary hydroxyl group and formaldehyde is primary hydroxyl group.




Loss of CH2O might be from a CH2OH group present in your molecule. Loss of water might be from a OH (or more in your case).

LC-MS is not so powerful if you know absolutely nothing about your sample. Which LC-MS are you using? Q-TOF, iontrap?

(1) I don't see water adducts either.
(2) The Chemspider search is a jolly good idea, but you'll have to do it again and make sure you use the right mass. The structures given are mostly charged carboxylic acids (negative ions), or ion pairs of things that would appear separately in ESI. Only one has two hydroxyl groups, and they're phenolic groups that are less easily lost.
(3) Are you sure you're looking at a hydrogen adduct? I can't remember which elements are included by default in Waters' mass-to-formula conversion.
(4) If you do have other adducts present, they may fragment differently and give you more information? Similarly, does it form a negative ion?
(5) Does the peak also have a UV absorbance or any other characteristics that might help?
(6) and yes, any information about the source of the sample is helpful! I find it easier to identify what a sample ought to contain from web and literature searching, and confirm by LC-MS, rather than identify from scratch... but don't tell any of my clients that! Analysis by wikipedia...

The numbers sort-of look familiar to me, but I can't think why, and after a while, all numbers start to look familar.