[Ravinder]

Purity Angle should less than purity threshold....Peak Purity Pass
Purity Angle more than purity threshold....Peak Purity fails.what is the reason

[Golden_4_Life]

I don't think we understand what Question you are asking?
Are you saying that "peak purity" fails when it has a low reading?

[AC Prabakar]

The system will measure the Peak purity in the following manner.
System will extract the spectrum of apex of the peak.
Then it will split the peaks into different parts(these values also can be given by user!).
Simply the system will compare the apex peak with all of the different parts.
Here the purity angle and threshold come in to picture.

Purity angle is the numerical value of the measured peak's apex.
purity threshold is the numerical value of the minimum allowable variation range.

If the  minimum allowable variation range is (purity threshold ) lesser than that of measured value (purity angle) peak purity passes.If not it will fail.