Peak Purity

<p><span>We are using peak purity (Purity angle and purity thresold) for demonstrating specificity (Interference and degradation) for analyte and impurity peaks. There is always an issue of peak purity failing for impurity and/or analyte peak, specifically in degradation. We have to process all of the injections with same processing method and it is very difficult to define max noise area for purity determination with no peaks in that area in all injections. Also, for peak purity the absorbance should be less than 1 AU. In all the related substances determination methods usually the absorbance is higher than 1 AU. Therefore, dilution is required. when you dilute sample, the impurity and degradant peaks disappear, so you have to consider peak purity of impurities in concentrated sample and analyte in diluted sample, which, we find time consuming and confusing.</span></p><p></p><p><span>Is that any alternative to peak puirty determination. Anyone using methods/practices ohter than purity angle and purity thresold? </span></p>


  • lizh

    This is an interesting question, there are a number of issues....

    (1) Max noise area definition - have you considered adding a little to the final hold time in the run and selecting this period as your noise threshold. It does mean you are at the highest background absorbance value if you are running a gradient. This will add to the overall run time, but should help.

    (2) The limitation of using purity below 1 AU. This is a limitation fo the algorithm/detector function. I am not sure if there is a good way around this.But I will check with some more experts

    In the end I think this is a challenge for absorbance and the best solution might be to add MS detection as your analyses are becoming so complex. A single quadruple could give could assurance that your purity results are valid.

    I will collect some more answers on this.


  • RMJ

    Does the 0.5 minute minimum recommended noise interval for peak purity calculations apply to Acquity data collected at 10 pts/sec or greater?

    I have found this suggestion in older Millennium/Empower software training for HPLC systems, and want to learn if a shorter time interval could be recommended for the Acquity at the higher data rates?

    Also, does the number of points across the noise interval become a factor, as it is for accurately defining a peak?


  • lizh


    Here is the comments on your question from the Peak Purity Algorithm mathematician who developed are right!


    Good question.

    The minimum noise internal is not an absolute value.

    Rather, the minimum time for the noise interval corresponds to a peak width (measured at 5% height)..

    So, way back when, 0.5 minutes value was an appropriate minimum.

    With ACQUITY, peak widths are narrower than 0.5 minutes, so the minimum time for the noise interval can be less.

    The customer is right.