Identification by GCMS using library standards--Have the protocols changed?

Identification by GCMS using library standards--Have the protocols changed?

Posted by Wayne Morris on Feb 1, 2015 12:54 pm

With the ever increasing use of libraries of standard mass spectra, have the instrumental analysis protocols for identification changed?  The protocols of analytical chemistry have always stated that the analyses of the  standard and the unknown samples should be done under the same conditions.  Obviously, library spectra are run on different insttruments and with under many circumstrances with different or unknown instrumnental parameters.  In some instrances, the standards are not readily available or cost prohibitive for the analytical lab to purchase.  So, can a "proper" identification be made?

Another issue, I have seen identifications made using ONLY the fragmeent masses rather than the relative intensities AND the fragment masses when comparing the spectra of  library standards and unknown samples.  All the protocals I have ever seen require that both be used. 

Finally, if the standard sample is not run on the same instrument at the relatively same time as the unknown samples, there is no retention time data available with GCMS and only the MS data is used and the identification via comparisons may be done using the above mentioned methods.  Was a "proper: identification made?  Een if another GC run is made using a different instrument and parameters, is that retention time match confirmation?  Or, if another test such as IR is done, is that sufficient for a proper identification, especially if the standard is also from a library?

So, what are your feelings towards this apparent change of analytical protocols?  And how, if you agree that the above issues do not matter, how do justify that opinion.  If you agree with my opinion that it is not proper, how to you handle it when you see such an "idetification" done?

Thank you, Wayne Morris
Wayne A Morris

Re: Identification by GCMS using library standards--Have the protocols changed?

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