In order of purity, from highest to lowest. This is the only universally accepted standard.
Chemicals are of the highest purity attainable.
Reagent Purity is generally equal to ACS grade. This grade is suitable for analytical work and is more than adequate for general lab use. USP grade may be used for most laboratory purposes. Lab An upper-level intermediate quality. Although this grade does contain impurities, it is usually pure enough for use in educational laboratories.