Empower Tip: Peak Purity

When creating a new Processing Method, be sure to select ‘PDA’ and click the ‘Purity’ tab. The default Spectral Contrast values appear.

The ‘Wavelength Limit’ should be set to start above the UV cutoff of the mobile phase and end at a value that includes all absorbances. Start with ‘MAX Plot’ and look at the UV spectra for the peaks of interest.

Enter the ‘Wavelength Limit’ in the ‘Start’ and ‘Stop’.

The ‘Noise Interval’ in minutes should be determined from ‘MAX Plot’ as well. This interval should be 2–4 peaks widths (at half height) long. Remember to multiply the ‘interval’ by the ‘Sampling Rate, from the Instrument Method, to calculate the number of data points in the interval, as it must contain a minimum of 12 points.

Zoom in on an area of the baseline that does not have any significant absorbance.

Enter the region determined from Step 5 into the ‘Noise Interval’ field.

Verify the ‘Noise Interval’ by selecting ‘Display Noise Spectrum’ from the ‘Spectrum Review’ menu. Each value plotted is the ‘root-mean-square noise’ at each wavelength in the spectrum. The shape of the noise spectrum should be random and not resemble the spectra from the peaks of interest. The noise spectrum is chemistry-dependent.

If the ‘Noise Interval’ contains less than 12 spectra, Peak Purity will NOT be calculated, and you will see messages in the Message Center indicating that the Noise Interval is invalid and does not contain sufficient spectra.

It’s that easy!