Hello,

ESI source in negative mode will be more accurate for mass spectral study of glycosides.

Usually EIMS didn´t give the molecular ion for glycosides, because these are thermically unstables. For molecular weight determination in glycosides you need another soft MS technique like FAB-MS which gives you a pseudomoelcular ion.

EI-MS often break down the molecular structure totally, so it is used for comparing fragment ion patterns with the library. If you want to get a pseudo-molecular ion of glycosides, I recommend you to use ESI- or FAB-MS instead.

It is highly unlikely that you will observe M+in EI. Try softer methods like FAB or MALDI if you are keen on the molecular ion peak

Dear Prof. Greetings

It seems that you forgot your work, done by your hands, by time!!! Did you forget Salvadoside which was measured by FAB-MS?  I miss you dear.

Dear Prof. M. Salah,

It is my pleasure to answer this question, I recommend soft ionization technique like FAB-MS or ESI-MS as the glycosidic linkage is very likely to break using EI-MS because the 70 electron volts (ev) are much more stronger than bond energy, if the bond energy can withstand 10 ev then a molecular ion peak could be observed, but this is not the case in most glycosides.

in ESI (electrospray ionization) the compound solution (in completely volatile solvent, i.e. no buffers with salts) is sprayed in heated ionization chamber fed with damping gas (noble gas like helium) under electric charge either in positive mode (usually for compounds easily acquiring protons such as alkaloids) or negative mode (usually for compounds easily losing protons such as phenolics).

further fragmentation could be enhanced using SIM mode with certain collision energy to confirm aglycone and sugar masses. or even to detect single amino acids in peptides.

FAB mass and chemical ionization is also a good candidate for such type of compounds.

Thanks a lot for all of you. I asked you because I have seen a paper published in a highly ranked Journal containing EI MS analysis for a glycoside with deoxy sugars. They determined its molecular weight depending on this analysis.

At least we now know that you were just looking for a confirmation of the negative