Empower Tip: Review Window and the Processing Method

If Empower indicates that a peak is not spectrally pure, we may want to know how many spectrally different components are under the peak. In this week’s tip, we will learn about Multi-Component Peak Purity. Multi-Component Peak Purity is an extension of Peak Purity by comparing combinations of spectra from within the peak to the other spectra within the same peak. As a result of these comparisons, Multi-Component Peak Purity helps to determine the number of spectrally different components under a chromatographic peak.

STEP 1 This is the sample we looked at in Tip 137 with the impurity spiked at the 20% level. The Purity Angle is much greater than the Purity Threshold and the Purity Plot indicates that the peak is not spectrally pure.

In the plot properties, we can annotate the plot to indicate the point of Maximum Impurity. This is point across the peak where the spectrum is the most different from the apex spectrum.

The Purity Plot is now annotated with the point of Maximum Impurity with a vertical line marked with M.

Multi-Component Peak Purity is found on the Purity tab of the Processing Method. From the Purity Pass drop down list, select more than one Purity Pass, in this case I have selected two.

What does the second pass do? On the first pass, the apex spectrum is compared to every other spectrum across the peak. This results in the calculations of the Purity Angle, Purity Threshold and the Purity Plot. On the second pass, Empower compares each spectrum across the peak to the range of spectral shapes that can occur from the additive combinations of the apex spectrum and the spectrum from the point of Maximum Impurity. This set of comparisons results in the calculation of a new Purity Angle, Purity Threshold and Purity Plot for the second pass. Additionally, a new point of Maximum Impurity is identified. This would be the spectrum across the peak that is most dissimilar to the additive combinations of the apex spectrum and the spectrum from the point of Maximum Impurity from the first purity pass.

Once the sample is re-processed, we see the results of the second Purity Pass. The Purity Angle is less than the Purity Threshold and the Purity Plot indicates both the point of Maximum Impurity from Purity Pass one, indicated by the 1, and the point of Maximum Impurity from the second pass indicated by the M.

If we zoom in on the Purity Plot for the second Purity Pass, we see that the Purity Angle plot is now below the Purity Threshold plot. This tells us that there are two spectrally different components under this chromatographic peak.

If the second purity pass still indicates an impurity under the peak, we can perform a third purity pass. If the third purity pass Purity Angle is less than the Purity Threshold and the Purity Plot agrees, then we can conclude there are three spectrally different components under the chromatographic peak. You can extend this logic to the fourth purity pass.

It’s that easy!