I hope others have given you a feel for the meaning. In some cases, they are totally unrelated.
Rolls Royce makes a quality car. How does purity apply at all in this case?
A chemical may be near 100% purity, but if it does not meet the required physical specifications (say granule size or bulk density) it is of poor quality.
"Whoever is spared personal pain must feel himself called to help in diminishing the pain of others. We must all carry our share of the misery which lies upon the world." -- Albert Schweitzer