Picking up on the connotative details of any language can be tough, and English is no exception. From native speakers to beginners, individuals often struggle to grasp some of its finer points. And though the results are rarely disastrous, they can be damaging and should be avoided whenever possible.
Not sure where such difficulties apply? Take [...]
1: Examination and determination as to characteristics (as weight, measure, or quality)
2: Analysis (as of a drug) to determine the presence, absence, or quantity of one or more components.
3: A substance to be assayed; also : the tabulated result of assaying
Determination of the relative strength of a substance (as a drug) by comparing its effect [...]