Empower Tip: Helpful Empower Tools

In this tip, we start a discussion about tools in Empower that can help with variations in peak retention times. It is not unusual to observe slight variations in peak retention time from injection to injection. If the variation in retention time becomes excessive this can result in peaks not being identified properly and consequently components not quantitated.

We start with a standard containing four components, all identified properly.

In the sample chromatogram Peak #3 has shifted and is not identified. The peak type is Unknown. The peak table also shows that Peak #3 is missing. Clearly, we see the peak at 8.033 minutes, however, Empower has not identified it.

If the peaks are well separated, we could increase the retention time windows around the peaks which would compensate for the shifts in retention time.

Another tool we have is the Retention Time Reference peak or RT Reference as it is called out in the Components tab of the Processing Method. A Retention Time Reference peak must be in every chromatogram and ideally, should be well separated from the rest of the peaks. As long as Empower identifies the reference peak, it will properly identify any peaks referenced to it. In this example, I have selected Peak #2 as the reference peak.

STEP 5:

This is the calculation for the temporary retention time used for peak identification. This does not change the expected retention time listed on the Components tab of the Processing Method.

Substituting in the real numbers: (4.842 / 4.889) x 8.146 = 8.068. The temporary expected retention time for the peak is 8.068 +0.091 minutes. Now the peak at 8.033 minutes falls within the new retention time window and is identified properly.

It’s that easy!