compound identification
Quote from Guest on February 6, 2023, 8:51 amHello,
i trying to analyze my first batch of chromatograms. In particular, there are calibration chromatograms where there should be toluene and alpha pinene on it. The peaks are visible, but the identification for toluene is always 3 methylpentane, and alpha pinene is only identified by gamma terpinene. (I use the NISTDEMO library)
If tried using different interval selection, as well as choosing different model components, but identification does not change, and i know the calibration gas does not contain these compounds. HOw could i approach this issue?Thank you very much
Hello,
i trying to analyze my first batch of chromatograms. In particular, there are calibration chromatograms where there should be toluene and alpha pinene on it. The peaks are visible, but the identification for toluene is always 3 methylpentane, and alpha pinene is only identified by gamma terpinene. (I use the NISTDEMO library)
If tried using different interval selection, as well as choosing different model components, but identification does not change, and i know the calibration gas does not contain these compounds. HOw could i approach this issue?
Thank you very much
Quote from Beatriz Quintanilla on February 6, 2023, 3:50 pmHello!
We advise you to get the full NIST library, since the demo version is not comprehensive enough and that could hinder the identification of some compounds. We assume the models calculated are good, but the identification step fails for that reason. In the meantime, you can check manually if the average spectrum modelled in PARADISe for each of those compounds match the ones available at the online version of the NIST library.
Note that, in any case, the identification of terpenes (alpha pinene, gamma terpinene) is tricky because their mass spectra are very similar, usually presenting the same main ions and maybe some slight differences on the intensity ratio. In your case, the use of internal standard allows to confirm which terpene is expected to find.
I hope this helps!
Best,
Beatriz
Hello!
We advise you to get the full NIST library, since the demo version is not comprehensive enough and that could hinder the identification of some compounds. We assume the models calculated are good, but the identification step fails for that reason. In the meantime, you can check manually if the average spectrum modelled in PARADISe for each of those compounds match the ones available at the online version of the NIST library.
Note that, in any case, the identification of terpenes (alpha pinene, gamma terpinene) is tricky because their mass spectra are very similar, usually presenting the same main ions and maybe some slight differences on the intensity ratio. In your case, the use of internal standard allows to confirm which terpene is expected to find.
I hope this helps!
Best,
Beatriz
Quote from Guest on February 7, 2023, 3:54 pmhello Breatriz,
thanks for the comment, it was really useful as this was exactly the issue. I had a library for my MSDOS chem station version, and it would not work if i put it in the NIST MSSEARCH forlder. So i had to convert it to the NIST MS software format.
I had many issues until i found this post: https://drchrispook.com/2021/04/08/convert-nist-mainlib-and-replib-ei-libraries-to-msp-format-to-annotate-gc-ms-data-with-ms-dial/
basically allowed me to export my "full" library to the NIST MS format into different subfiles, I did not even need to merge them, i simply loaded these many libraries in the MS Search programme and it worked!
thank you very much
Best regards
hello Breatriz,
thanks for the comment, it was really useful as this was exactly the issue. I had a library for my MSDOS chem station version, and it would not work if i put it in the NIST MSSEARCH forlder. So i had to convert it to the NIST MS software format.
I had many issues until i found this post: https://drchrispook.com/2021/04/08/convert-nist-mainlib-and-replib-ei-libraries-to-msp-format-to-annotate-gc-ms-data-with-ms-dial/
basically allowed me to export my "full" library to the NIST MS format into different subfiles, I did not even need to merge them, i simply loaded these many libraries in the MS Search programme and it worked!
thank you very much
Best regards
Quote from Guest on February 7, 2023, 3:58 pmQuote from Guest on February 7, 2023, 3:54 pmhello Breatriz,
thanks for the comment, it was really useful as this was exactly the issue. I had a library for my XP chem station version, and it would not work if i put it in the NIST MSSEARCH forlder. So i had to convert it to the NIST MS software format.
I had many issues until i found this post: https://drchrispook.com/2021/04/08/convert-nist-mainlib-and-replib-ei-libraries-to-msp-format-to-annotate-gc-ms-data-with-ms-dial/
basically allowed me to export my "full" library to the NIST MS format into different subfiles, I did not even need to merge them, i simply loaded these many libraries in the MS Search programme and it worked!
thank you very much
Best regards
Quote from Guest on February 7, 2023, 3:54 pmhello Breatriz,
thanks for the comment, it was really useful as this was exactly the issue. I had a library for my XP chem station version, and it would not work if i put it in the NIST MSSEARCH forlder. So i had to convert it to the NIST MS software format.
I had many issues until i found this post: https://drchrispook.com/2021/04/08/convert-nist-mainlib-and-replib-ei-libraries-to-msp-format-to-annotate-gc-ms-data-with-ms-dial/
basically allowed me to export my "full" library to the NIST MS format into different subfiles, I did not even need to merge them, i simply loaded these many libraries in the MS Search programme and it worked!
thank you very much
Best regards