I have some organic molecules (carbamate derivatives) they show UV absorption yet looking in the mass scan , I can not see any ionization , I have tried positive and negative mode of ionization and nothing worked, I use a concentration of around 100 microgram/ml, any suggestions from mass experts. Instrument used is UPLC-UV-MS-MS by Waters.
Dear Salah, carbamate derivatives tend to fragment quite extensively in mass spectroscopy. Try to look for obvious fragments if parent ion is not visible.
Eg. -44 and -100 for Boc derivatives.
If you want to increase the parent ion try to reduce the cone and lens voltage.
Dear Fillipo,
I guess the extensive fragmentation is possible if we use EI but we are using ESI ( a soft technique which should cause slight or no fragmentation) , also the cone and lens voltage are applicable with EI sources as far as I remember. Thanks a lot for offering advice
The carbamoil group is easily breakable even with ESI, so given all worked properly in your case you may not see the intact molecule due to breakage and transpositions. Here is a paper who explain this phenomenon and a protocol they used to overcome this issue.
http://www.sciencedirect.com/science/article/pii/S1044030505000528
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