Primærstandarder

Primærstandarder, or primary standards, are highly pure chemical substances chosen for their well-defined composition, high stability, and minimal interaction with air or moisture. They are used to prepare standard solutions and to standardize titrants, reagents, and instruments in analytical chemistry. A primary standard should have a known molar mass, be readily weighed as a stable, anhydrous solid, and retain its purity over time under proper storage. Because of their properties, primary standards are typically dried before use and stored in tightly closed containers, often in desiccators, to minimize moisture uptake and CO2 absorption.

In routine analytical practice, primary standards enable accurate and traceable concentration determinations. They underpin volumetric analyses, including acid–base, redox, and complexometric titrations, by providing concentrations that can be calculated from mass and known stoichiometry. Secondary standards may be prepared from primary standards, but primary standards remain the reference against which other materials are calibrated.

Common examples of primary standards include potassium hydrogen phthalate (KHP) for acid–base titrations, anhydrous sodium carbonate for standardizing strong acids, and redox standards such as potassium dichromate (K2Cr2O7) or sodium oxalate under appropriate conditions. Other materials, such as ceric ammonium sulfate, are used as primary standards in specific redox systems. The choice of a primary standard depends on its purity, stability, non-hygroscopic nature, and the feasibility of accurate mass determination.

Overall, primærstandarder are foundational to accurate quantitative analysis, enabling reproducible and traceable measurements in laboratories.