Purity is better understood as a degree to which the substance containing impurities over and above which it can become toxic, unhealthy, unfit for consumption or no longer usable for some applications.
Any real substance like water or gold will always contain some impurities and never be 100% pure.
Abstract things like trust, love, hope, etc. can’t be measured and assessed a degree of purity. Managing emotions successfully in general, depends a lot more on the ability to apply relational and cognitive skills grounded in well understood psychological principles.