Peak Identification: Use Update RT - Tip 311

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Article number: 251608

OBJECTIVE or GOAL

Use Update RT in peak identification.

ENVIRONMENT

Empower
Tip of the Week #311

PROCEDURE

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

STEP 2
in the second injection, the third peak is not identified. We know the third peak is benzoate (Figure 2).

STEP 3
Possible solution: The Update RT field on the component tab of the Processing Method can be used in the following way (see Figure 3):

This function does not replace the Retention Times specified in the component table of the Processing Method. It updates for peak identification purposes only.
Replace and Replace Standards should be used when retention time shifts are consistent (either increasing or decreasing) and there are no extra peaks that could be misidentified.
Average and Average Standards should be used when retention times fluctuate around a mean value and there are no extra peaks that could be misidentified.

STEP 4
The updated retention time will appear in the Calibration window. With the Update RT set to Never, the function is turned off. If you look at injection 1 side-by-side with the Calibration window, you see that the expected retention time, as per the Component tab, is 8.140 minutes and the time in the Calibration window is 8.140 minutes (Figure 4).

STEP 5
Set the Update RT to Average standards (Figure 5). Because there are three injections of the standard, Empower will use the following formulae to update the expected Retention Time for the peak:

For injection 1 - (RTct+RTinj1)/2=Average#1
For injection 2 - (2x(Average#1)+RTinj2)/3=Average#2
For injection 3 - (3x(Average#2)+RTinj3)/4=Average#3

Where RTct is the Retention Time of the component from the Component tab and Rtinj# is the Retention Time of the component from the current injection.

STEP 6
For injection 1, the retention time of the peak is 8.150; therefore, the calculation for expected retention time is (8.140 +8.150)/2, which equals 8.145 minutes. That can be seen in the Calibration window in the Time field (Figure 6).

STEP 7
For injection 2, the retention time is 8.141667; therefore, the calculation for expected retention time is (2x(8.145)+8.141667)/3, which equals 8.144 minutes (Figure 7). That can be seen in the Calibration window in the Time field (Figure 7).

Important Note: If you had selected Average instead of Average Stds, the averaging process for the expected Retention Time would continue through all of the sample injections.

ADDITIONAL INFORMATION

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