Chromatography Forum

is there any possibility to identify the isomer ( o-,m-,p- isomer) by the fregmentation pattern of mass.
if yes then what is the region.

The answer, of course, is yes.

The fragmentation may need to be asscoiated with benze ring broken and re-arrangment.

If you have some training on pahyscial organic chemistry, you may have a better understanding on it. If not, I suggest you read some related book.

Yes, physical organic will certainly help in understanding, but you will need a good book on MS (McLafferty?) to get concrete ideas.

I assume you are talking about electron ionization(EI). Some compounds, like the regioisomers of xylene, give identical EI mass spectra. These compounds have to be differentiated by their retention times. You can tell that the spectrum is that of xylene, but you cannot tell which isomer of xylene. If the substituents have functionality in the form of heteroatoms, your can sometimes distinguish between the spectrum of the ortho isomer and the spectra of the meta and para ionomers. You will most likely need to use retention time, again, to distinguish between these latter two isomers. This difference between the EI mass spectra of an ortho isomer and the meta and para isomers is due to the ortho effect.

LCR is offering a course over the Internet on the interpretation of mass spectra beginning January 17, 2008. You may want to consider taking that course. Jack Watson and I have just published the fourth edition of Introduction to Mass Spectrometry: Instrumentation, Applications, and Strategies for Data Interpretation. This book provides a great deal of information regarding EI fragmentation.

The xylene spectra issue was one of the main sales points for the the GC- IRD (IR Detector.) IR detectors are capable of differentiating the isomers. For a price.

Best regards.