How to use thresholds for fractionation in PurityChrom?

PurityChrom gives you the possibility to fractionate peaks via thresholds. This is an optimal fractionation method for well baseline separated and defined peaks. A threshold is set at a specific UV Level as indicated in the example by the blue line. If a signal is overstepping this value, fractionation will be automatically started. If the signal falls below the threshold, fractionation will be stopped, and the valve will switch back to waste position. Both levels can also differ. Be aware that if a peak also consists of a shoulder, which is above the threshold, this shoulder will be collected in the same fraction.

You can also combine the limiter with a threshold. Every fraction, that is recognized by the threshold settings, will be divided into smaller sub-fractions by the limiter function and thus, fractions will not be bigger than the defined limiter value. If you adjust the limiter volume according to your working flowrate and regular fraction sizes, you will minimize contaminations by peak shoulders.

The fractionation via threshold can be defined in a method (time control file) using the threshold tab. Here you can specify at which start and end point the threshold function should be active and which level of signal is triggering the threshold actions. It is important to define the actions that should be carried out upon exceeding or undershooting the signal. This you can do by clicking on the red dots indicated in the screenshots. After defining all parameters for the threshold function, don´t forget to insert them into your time control file by using the button “insert”.

If you want to have different UV values for start and end point of your fraction collection, simply add two thresholds with different UV signal intensities and then define for one only the “Over Event actions” and for the other only the “Under Event actions”. When you would like to combine the limiter and the threshold, simply add the “fraction limiter” command to your method.

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