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.
"Success is not measured by what you accomplish but by the opposition you have encountered, and the courage with which you have maintained the struggle against overwhelming odds." -- Orison Swett Marden