Empower Tip: Review Window and the Processing Method

In this tip, we are going to learn why it is important to align chromatograms when collecting data from both a PDA and a QDa mass detector (Part 5).

If the PDA and QDa are connected in series, there will be a small offset between the two chromatograms. If you want to properly compare the chromatograms, you need to compensate for the offset. Furthermore, Empower uses the retention times of the peaks from the UV chromatogram to extract the MS spectra for those peaks.

The UV chromatogram and the retention times of the peaks are displayed.

From the 2D Channels tab, we can select the TIC plot and overlay it with the UV chromatogram. (Be sure to click the Autoscale tool to correct for the difference in scaling.) You can see that the peaks in the TIC plot elute slightly later than those in the UV chromatogram.

Click on the ‘TIC plot’ and you can see the MS spectra for the peaks in Spectrum Review. The retention times in the Spectra table are taken from the peaks in the UV chromatogram.

We can correct for this offset in the Smoothing/Offset tab of the Processing Method by entering a small offset.

Reprocessing the injection with the revised Processing Method gives us a better overlay of the chromatograms and the retention times of the spectra are corrected to correspond to the peaks in the MS chromatogram.

It’s that easy!