Noisy leading spectrum in purity view of mass analysis window in Empower using an optical detector and a MS in series - WKB71256

SYMPTOMS

• Leading spectrum in purity view of the mass analysis window is noisy
• Trailing spectrum is not noisy
• Optical detector and mass spectrometer are installed in series (no ISM/split module)
   

ENVIRONMENT

• Empower

CAUSE

Because the two detectors are installed in series, the signal reaches the optical detector before it reaches the mass spectrometer. This causes a difference in retention time  that needs to be compensated for during combined processing of optical and MS data.

FIX or WORKAROUND

1. Determine the time difference between the optical and MS detection in the mass analysis window by comparing the UV and TIC/XIC traces. In the example screenshot below, the delay is approximately 0.005 minutes.
   
    
2. In the processing method, enter the observed time difference as a negative value in the MS Channel Time offset of the Smoothing/Offset tab. It is recommended that you set the leading and trailing spectra extraction points to 30% (default 10%) to avoid MS spectra extraction from the extreme ends of the front and tail of the peak.
    
3. Reprocess the data; data signals of optical and MS detection now align, and both leading and trailing MS spectra are free of noise.
   
    

ADDITIONAL INFORMATION