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UNIFI 3D peak detection is missing expected masses - WKB23327

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Article number: 23327

SYMPTOMS

  • Processing data with the UNIFI 3D peak picking process (or 4D peak picking process for Vion data) fails to detect all expected component peaks
    • For example, during analysis of a component containing bromine, the 79Br component was identified by the 12C main isotope, but UNIFI Component Summary did not assign the 81Br isotope. Even the 81Br isotope was always missing from the 3D spectrum.
  • Looking manually into the data set in Investigate, the missing spectrum peaks can be identified, and in the 3D plot of the isotopic pattern they are clearly present.

ENVIRONMENT

  • UNIFI 1.8.2
  • UNIFI 1.9 SR4
  • UNIFI 1.9.9
  • UNIFI 1.9.12
  • UNIFI 1.9.13
  • waters_connect UNIFI app (all versions)

CAUSE

When using Chromatographic Peak width = automatic in the 3D Peak Detection settings or 4D Peak Detection settings, UNIFI may fail to correctly identify peaks.

This is a problem with chromatographic separation. It occurs where peaks are poorly resolved, such as peaks that overlap and result in shoulders, or small peaks on the fringes of more intense peaks.

When Chromatographic Peak Width is set to Automatic, UNIFI determines the average peak width of all the 3D chromatographic peaks in the specified retention time range, and it applies that to all of the data. You can see the automatically determined peak width for a given sample by opening the 3D Viewer on the Investigate tab, which shows a plot of m/z versus retention time. Red dots show all the detected chromatographic peaks. Select the Peak Processing Information table to view the average peak width of all the detected peaks (that is, the value used for 3D peak width if you select Chromatographic Peak Width = Automatic in 3D Peak Detection.

FIX or WORKAROUND

  1. On the Investigate tab, find the average peak width of all the detected peaks in the data as described in the "Cause" section above.
    1. Open the 3D Viewer on the Investigate tab of the Analysis.
    2. Select the Peak Processing Information table to view the average peak width of all the detected peaks.
  2. In the Analysis, select Edit > Analysis Method.
  3. In Peak Processing Settings, select Find 3D Peaks.
  4. In 3D Peak Detection, go to Chromatographic Peak Width, select the Manually Specify Peak Width check box, and set Peak Width to less than half the average peak width value that you found at step 1b.
  5. Click the Update button at the top-right of the screen.
  6. Go back to the analysis Results.
  7. Select Process to apply the new peak detection settings.
  8. If the peak of interest is still not assigned, repeat step 4, lowering the peak width value in steps of 0.005 minutes.

ADDITIONAL INFORMATION

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