A highly purified chemical that is directly weighed or measured to produce a solution whose concentration is exactly known is referred to as a:

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A primary reference material is a highly purified chemical that is directly weighed or measured to produce a solution whose concentration is exactly known. Calibrators are also used in analytical chemistry, but they are not necessarily directly weighed, and their concentration may not be exactly known. Secondary standards are materials that are calibrated against primary reference materials. Working solutions are solutions prepared from primary or secondary standards to be used for analysis, but they are not directly weighed or measured like primary reference materials.

A Highly Purified Chemical That Is Directly Weighed or Measured