Tip #255: Peak Purity Parameters for PDA Data

Welcome back to Get Empowered! In this week’s tip for Empower Chromatography Data System (CDS), we will discuss Peak Purity parameters for Photodiode Array (PDA) data. (In last week’s tip, we discussed the Spectral Contrast parameters for PDA data, Tip #254).

Let’s get started.

Step 1

On the ‘Purity’ tab of the Processing Method there are several Purity Parameters. To begin, check the ‘Purity Enabled’ box to have Peak Purity calculated. The Active Peak Region (%) defaults to 100.0. This means Peak Purity will be calculated using all spectra from ‘peak liftoff’ to ‘peak touchdown’ (figure 1).

Figure 1

Step 2

If the baseline is noisy, you may want to enter a value less than 100.0 to ensure Empower does not use noisy baseline spectra to calculate Peak Purity (figures 2 & 3).

Figure 2

Figure 3

Step 3

The Threshold Angle can be calculated in a variety of ways. Typically, it is the sum of the Noise Angle (which is based on the noise interval selected) plus the Solvent Angle. It is recommended to try AutoThreshold first. AutoThreshold determines the Solvent Angle for each peak in the chromatogram. The Solvent Angle is automatically calculated as a function of the Maximum Spectral Absorbance (MSA) of a peak. MSA is the maximum value of baseline-corrected spectral absorbance for a peak. AutoThreshold does need to be validated and there are some limitations (figure 4):

Figure 4

• Make six injections of the standard (figure 5).

Figure 5

• Create a PDA Processing Method and follow Steps 1 & 2 above.
• Determine the ‘Noise Interval’ as described in Tip #254.
• Set the Threshold Angle to ‘AutoThreshold’.
• Process the six injections. If the ‘Purity Angle’ is less than the ‘Purity Threshold’ for all peaks in all injections, then AutoThreshold is working (figure 6).

Figure 6

• You can use the Threshold Angle obtained from AutoThreshold for Peak Purity testing on any unknown, as long as its maximum spectral absorbance is less than 1.0 AU and less than five times the maximum spectral absorbance of the standard used to develop the method.

Step 4

If the Purity Angle is greater than the Purity Threshold for any of the peaks, in any of the standard injections, you need to determine the Solvent Angle separately. That will be described in next week’s Tip #256.

It’s that easy!

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

Please rate this Empower Tip of the Week

Next time in Empower Tip #256– we will continue our series on Peak Purity using both PDA and QDa Detectors.

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