Derived channels for peak purity determination

Hi there,

 I have a query about what derived channels should be used to process peak purity results from.  Our company seems to have adopted processing a derived channel from either 1) MaxPlot or 2) the prescribed (single) analytical wavelength for the method being interrogated.

 Q/ If you were writing a SOP / instructional document what would you prescribe and why?

We understand that you would use MaxPlot to set/check for a suitable noise region and to ensure maximum absorbances aren’t above 1 AU.  However, does it matter what derived channel is used for actual peak purity processing?  Peak integration would be (slightly) different between the two derived channels, but for actual peak purity determination wouldn’t you get to the same result (more often than not) regardless of what derived channel was processed?

Best Answer

  • Accepted Answer
    @rob_burgessI would recommend using MaxPlot when developing the processing method for the reasons you describe - selecting a proper noise interval and making sure that all peaks do not exceed 1.0AU.  I would then recommend using an appropriate wavelength for your quantitative analysis.  It is not unusual to see a small difference in the peak purity results generated from MaxPlot as compared to peak purity results generated from a particular wavelength because of slight differences in the integration of the peak from one to the other.


  • Peak purity processing looks at the PDA spectrum collected across the peak for the analyte of interest. It then compares this spectrum to that of the same compound in your reference standard.

    In the purity setup for the processing method you specify wavelength range, noise window, threshold criteria, and purity passes. These parameters are what you want to provide guidance around depending upon the application.

    For example, if your mobile phase has a UV cutoff of 240 nm you don't want to use a spectral window of 190 - 400 nm through which you are determining peak purity.

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