Peak Identification: Using Retention Time Reference Peaks - Tip 310

OBJECTIVE or GOAL

Use Retention Time (RT) reference peaks.

ENVIRONMENT

• Empower
• Tip of the Week #310

PROCEDURE

STEP 1
The Processing Method is developed with a standard, and the peaks are named accordingly (Figure 1).

STEP 2
We run a sample and see that there is a peak at 8.033 minutes that has a Peak Type of Unknown. Peaks 3 and 4 show "Peak Type Missing" (Figure 2). 

STEP 3
In this example, the peak at 8.033 minutes is Peak 3. The expected retention time is 8.146 + 0.058, so it is not identified properly. This means that the peak needs to fall in the range of 8.088 – 8.204 to be identified properly (Figure 3).

STEP 4
Make Peak 2 the RT reference peak in the RT Reference field on the Components tab of the Processing Method (Figure 4). 

Empower makes the following calculation:

(RT of RT Ref Peak in Sample/RT of RT Ref Peak in Standard) x RT of peak of interest in the standard, where RT = Retention Time 

Substituting in the actual numbers: (4.842/4.889) x 8.146 = 8.068

STEP 5
The expected range for the peak is now 8.068 + 0.058, which translates to 8.010 – 8.126 and the peak is identified properly (Figure 5).

STEP 6
You now have the option to identify the peak via the Relative RT Reference value rather than absolute retention time (Figure 6).

Important things to keep in mind when using RT Reference peaks:

• The RT Reference peak must be in every chromatogram.
• This is applicable to chromatograms where the peaks are close together or the RT Windows must be kept small.
• This adjusted retention time is for peak identification purposes only; it does not affect the calibration curve.
• You can add the "RT Reference used" field to the peaks table in Review and to the report, to quickly identify the RT Reference peak used without having to go back to the processing method.
   

ADDITIONAL INFORMATION

This can be done with either the Pro or QuickStart interface.