|Waters Synapt G2-Si - multiple issues to access CCS values||nicolas macorps||2022-08-31|
Dear Skyline support,
I have been trying to use Skyline to analyse data obtained with a Water Synapt G2-Si with ion mobility (IM) experiments. Experiments are performed with the HDMS mode (ion mobility, elution time and full scan MS only). The ion mobility technique is TWIMS that use a calibration curve (mob_cal.csv file in the sample root) that the proprietary software uses to correlate measured drift times to CCS values.
I want to use Skyline.ms to have a solid workflow with this software to quantify PFAS (small targeted molecules) in various samples. To confirm that I am indeed looking at a PFAS, I need to access CCS values (which include the need to create an IM library) so I can then have it when exporting a "report'.
I encountered some issues when using Skyline features which is why I am opening this support feed. You can find uploaded in the "File Sharing Folder for Skyline Support" my folder under the name "Synapt_CCS_PFAS_SkylineSupport.zip". This file contains *.raw data from the Water Synapt, *.sky file (with the trageted list molecules in a *.csv in case it is needed) and snapshots of some error message I got along my tests.
1) Skyline crashing when importing *.raw files :
When trying to import Synapt *.raw files (220621008.raw and 220621009.raw in the *.zip folder), skyline crashes at the importation step (software closes without error message). This issue was encountered and reported in another support feed. The proposed solution in this feed was to convert *.raw into *.mzML files, but it seems that this approach doesn't allow for CCS values when creating IM library.
I went looking into the *.raw folders and found that when changing _FUNC002.DAT into _FUNC002.temp (in other words I "remove" this function from the *.raw file) I was now able to import without crashing the *.raw file and was able to obtain chromatograms with full scan spectrum and drift time (ms) distribution.
I initially thought that this "Function 2" contained "lockmass" data which can cause some issues when converting into *.mzML so I thought that removing this function could fix the problem. However I cannot be sure that this function is indeed the "lockmass" when looking in the "_extern.inf" file nor in the "_HEADER.TXT". The only information I have on these files are for the function 1 : "MOBILITY MS FUNCTION". So function 2 may also contain IM data from the HDMS experiments but I cannot be sure.
In any case, I kept going with modified *.raw files with the change of _FUNC002.temp (220621008_modify.raw and 220621009_modify.raw) to try to obtain CCS values
2) Negatives CCS values when creating IM library with "use results"
Now having something to work with, I tried creating the IM library for my molecules. I was happy to see that I could obtain some CCS values by doing so. Unfortunatly they are all with a negative sign and as such completely incorrect. I had two thought on that :
- Conversion of drift time into CCS values using the mob_cal.csv file (as done by the proprietary software) is not performed in Skyline in this manner or Skyline needs another type of file to do so.
- We need the function 2 to be active to have CCS values
For the latter, I tried to reactivate the function 2 in the *.raw file and reimport them. Doing so led to no crash so I followed with the creation of an IM library. I ended up with an error message "Failed using results to populate ion mobility library: [SpectrumList_Waters:spectrum()] Bad index: 18446744073709551615" (you can find the snapshot in the *.zip file and the extended error message in a *.TXT file in the *.zip).
Further trying with reimportation led to a crash of the software as mentionned in my first point.
I hope you have enough elements with this description to help me ?
- Do you know why Waters HDMS experiment *.raw files would make the software crash ?
- Do you know why I have negative CCS values when creating the IM library with the "use results" feature?
Let me know if you need anything else from me.