OpenLab CDS Peak Identification in New Sequences

Hi all,

 

I am analyzing petroleum samples with a GC-MSD and I'm having trouble getting the software to identify peaks using OpenLab CDS (v. 2.5). I have optimized the data processing method for peak IDs based on standards and unknowns for a particular sequence, but when I upload a different sequence I cannot get the processing method to correctly ID some peaks even after I update the expected retention time (RT) for the time reference peak(s).

 

I have assigned 1-2 time reference peaks with large absolute RT windows (1.5-4 min) for each EIC. These reference peaks are easily identifiable and the large window should accommodate run-to-run RT shifts. The other peaks of interest have smaller absolute RT windows (0.1-0.2 min). In some cases, I made the RT window larger (~0.3 min) to ensure that the peak was correctly identified (see example below), but the software still refuses to ID the peak correctly. 

 

For example, in the chromatogram below the peak of "C25 22S Tricyclic" should be the left peak in the doublet (~44.25 min). As defined in the Compound ID table below, the targeted peak is the first peak within the RT window, but is still not assigned correctly. I also changed MS purity to 0% in the Compound Spectra section of the method to ensure this issue was not caused by a spectra mismatch between the reference and sample. 

 

 

 

I realize I could right click on the peak at 44.25 min, go to Assign Peak..., select the peak name, and check "update RT in the method". This will fix the issue in this sample but when I "Reprocess All", it leads to new misidentifications of the peak in other samples. Do I have to create a new processing method for each sample and update expected RTs for all "missing" (i.e. unidentified) peaks? That seems laborious and something that should be resolved using time reference peaks and appropriate RT windows.

 

Any advice you can give would be greatly appreciated. Thank you!

  • Hello,

     

    I am not seeing anything outwardly wrong with your method settings from what I can see of them in your screenshot. I would need to look at your data and method firsthand to investigate this issue. If you are OK with posting your data online, you can attach your result set (exported from Data Analysis as a .olax file from the Data Selection view) to a reply on this post. Otherwise I would recommend that you contact your local Agilent support for assistance: https://www.agilent.com/en-us/contact-us/page  

  • Hello,

     

     

     

    Okay here is a example of a common problem when using reference peaks. I am not sure this is your issue in this case, but is a typical problem users have with the concept. 

     

    In this example, I have data that has shifted earlier than the ERT by about 0.1 minutes. Peak D is my reference peak but the window is too narrow to pick it up. Typical as you stated the window size for reference peaks is wider to ensure identification. 

     

     

    The only change I made here is to widen the identification window for Peak D and reprocess. As you can see all the peaks are found even though the non reference peaks are not in the ERT window for the method. This is because the ERT window has been corrected for each injection by the delta of the ERT to the actual RT of the reference. 

     

     

     

    Now if I update the ERT of the reference peak only, either by using the right click menu or just typing in the ERT in the method and reprocess you can see the other peaks are no longer identified. This is because the reference is identified and the delta between the ERT and actual RT is much smaller and does not compensate for the non reference peaks. To once again make this work I need to update all the other peaks ERTs in the method. 

     

     

    Marty Adams

  • Thank you all for your help! In some cases I was updating the ERT for the reference peak and that was partially the problem.

     

    One issue I am still running into is the software only sometimes accounts for peak shifts. In the examples below, I loaded the method with this compound table and settings.

    It correctly identifies peaks in this chromatogram...

    But doesn't identify peaks in another chromatogram (processed with the same method)...

    In the second chromatogram, the peaks are all shifted ~0.1 min to the left but the software is not identifying the compounds.

     

    Any idea of why this may be? The compound windows seem appropriate and the peaks of interest are the largest in their respective windows.

     

    Thank you again for your help!

  • Hello,

     

    Does the result set log give you any errors or warning about the identification?

     

     

  • jwycech,

     

    One thing you might try is reprocessing with clear corrections and see if that changes anything.

     

    Marty Adams

  • Interesting, there are no errors/warnings listed for the sample with the unidentified peaks shown above.

     

    It's a long shot but the computer that came with the instrument has weak processing power (i5 processor, 8 GB of RAM). Perhaps the software is timing out before it can properly ID peaks? The reprocessing is notably slow (~1 minute per sample).

Was this helpful?