Primary and Secondary standards

Introduction Primary and Secondary standards

The standardization process involves comparing a solution to a standard solution to determine its precise concentration. We used standard substances in standard solutions and knew their concentrations precisely. Traditionally, standard solutions are classified as either primary or secondary standards. A primary standard is used to standardize a secondary standard solution. Secondary standards are useful for a wide range of analytical experiments.

Biological standards are materials that contain the substance of interest at a known concentration. Measurement units can also be specified.  This standard can also be used to test new materials to determine their concentration. As a result, primary standards are used as primary calibrations or primary reference materials. A solution having a low reactivity and high purity is called a primary standard solution. Compared to primary standards, a secondary standard is less pure and more chemically reactive.

Functions of primary and secondary standards

  • The standardizations of volumetric solutions.
  • The purpose of this references is to determine unknown concentration using it.
  • Calibration of instruments.
  • The preparation of secondary standards.

Primary standards

Primary standards are chemicals or reagents with specific properties,

  • They are pure substances: Primary standard materials must be a chemical that has been prepared from extremely pure materials and have a high degree of purity, preferably 99.98%. Chemistry labs use chemicals of different grades of purity. The label states the purity percentage. For primary standards, it is appropriate when the chemical is at least 99.98% pure.
  • High degree of stability: When it is pure, it should have a high degree of stability, meaning it won’t react easily. It should be relatively inert, to put it more accurately. Reagents that react readily with air, water, or other molecules may not be dependable if they are unstable or change over time. Chemicals that are unstable and unreliable cannot be used as standards.
  • It should be anhydrous as possible: Salt should be anhydrous or dehydrated, means that its molecular structure should not contain water molecules.
  • There is less hygroscopicity: It is not enough to have anhydrous properties. When the container is opened, it is preferable if the chemical is less hygroscopic because water molecules are absorbed.
  • Easy to weigh: The material’s pure nature allows it to be easily weighed because its weight is a true representation of its actual molecular weight.
  • The molecular weight of this substance is very high
  • It must be available and ready for use
  • It should be nontoxic
  • It should be cheap

Secondary standards

Secondary standards include laboratory standards used in the production of chemicals, reagents, kits, or quality control materials for other businesses. Primary standards are used as primary calibrators or primary reference materials. Whereas secondary standards are smaller labs for the calibration of control materials, which is used for analyzing unknown concentrations of substances.

Secondary standards function primarily to perform external quality control on smaller laboratories. The secondary standard needs to be standardized and compared in order to be applied to the primary standard.

An aqueous solution of high purity must be used to prepare the secondary standard solution. Water must be deionized when used as an aqueous solvent. Standard solutions prepared without pure solvent are worthless.

Chemicals and reagents classified as Secondary standards have specific characteristics, such as;

  • It is less pure compared to the primary standard.
  • Stability is less than primary standards.
  • The solution of secondary standard comparatively remains stable for quite long time.

They are also referred to as chemicals that satisfy standard chemical requirements but fall short of primary standards.


A standard, also known as a calibrator, is a material that contains a known concentration of a substance of interest that can be expressed with definite numbers and units. It is classified into two types: primary and secondary.

When compared to the secondary standard, the primary standard is purer, more stable, less reactive, anhydrous, and less hygroscopic. Secondary standards are titrated or calibrated against primary standards and used as a reference material for analysis in all labs across the country. To maintain the standard’s quality, the solution should be prepared with pure, de-ionized aqueous solvent.

A primary standard serve as a primary reference material in a clinical lab setting. In laboratories, secondary standards are used as an external quality control to calibrate internal quality control. Unknown sample is analyzed after both external and internal quality check is complete and satisfactory.

Frequently asked questions

What are the criteria for primary standard?

Primary standard must have high state of purity, stability in air and solution, solubility, reasonably high formula mass.

What is the example of primary standard?

Sodium carbonate, potassium hydrogen iodate, potassium dichromate, oxalic acid etc. are the examples of primary standard.

What are the essential properties of primary standard?

A primary standard is a reagent that is very pure, stable, non-toxic, not hygroscopic and has high molecular weight.

What is secondary standard?

As secondary standard is a chemical or reagent which has certain properties such as, less pure than primary standard, less stable and more reactive.

What are the features of secondary standard?

Secondary standard is hygroscopic, more reactive, less stable. Their solutions molarity changes after some times.

What are the examples of secondary standard?

NaOH is one example of secondary standard.

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