Sure, but the reagent tests are really just qualitative, there's no good way of telling that the heroin I just bought from the nice man on the street corner is

Sure, but the reagent tests are really just qualitative, there's no good way of telling that the heroin I just bought from the nice man on the street corner is twice as pure as last weeks. I suppose there may be some tests that can tell if there is fentanyl present, which might help...?