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Primary and Secondary Standards

The process of standardization involves comparing a solution to a standard solution to determine its exact concentration.
The process of standardization involves comparing a solution to a standard solution to determine its exact concentration. In standard solutions, we use standard substances and know their concentrations accurately. Traditionally, we label standard solutions either as primary standards or secondary standards. A secondary standard solution is standardized through a primary standard. Secondary standards can be used for a variety of analytical experiments.

Materials that contain the substance of interest at a known concentration are called biological standards. Units of measurement can also be specified. New material can be tested using this standard to determine its concentration. Primary standards are therefore used as primary calibrators or primary reference materials.

Functions of these primary and secondary standards
  1. The standardization of volumetric solutions
  2. The purpose of this reference is to determine unknown concentrations using it
  3. The preparation of secondary standards
  4. Calibration of instruments.
Primary standards
Primary standards are chemicals or reagents that have particular properties, especially

1. This is an incredibly pure substance
Primary standard materials should have a high degree of purity, preferably 99.98%, meaning they must be a chemical that has been prepared from very pure materials. There are various grades of purity of chemicals in chemistry labs. The purity percentage appears on the label. It is a suitable material for primary standards when the chemical is pure to 99.98% or more.

2. High level of stability
It should have a high degree of stability which means it will not easily react when it is pure. A more accurate expression would be that it should be relatively inert. If a reagent is unstable or changes its properties over time, it may not be reliable, since it reacts easily with air, water, or other molecules. Unreliable and unstable chemicals cannot ever be used as standards.

3. As anhydrous as possible
Salt should be anhydrous, meaning that its molecular structure contains no water molecules.

4. There is less hygroscopicity
Having anhydrous properties is not enough. It is preferable if the chemical is less hygroscopic than water molecules are absorbed when the container is opened.

5. The molecular weight of this substance is very high

6. Easy to weigh
The pure nature of the material allows it to be weighed easily since its weight is a true representation of its actual molecular weight.

7. It must be available and ready for use

8. Ideally, it should be nontoxic

9. It shouldn't cost too much

Secondary standards
Laboratory standards such as those involved in producing chemicals, reagents, kits, or producing quality control materials for other businesses are considered secondary standards. Primary standards are used as primary calibrators or primary reference materials. Additionally, secondary standards are used in smaller labs for the calibration of control materials, which is used for analyzing unknown concentrations of substances. As such, secondary standards function primarily to perform external quality control on smaller laboratories. To apply the secondary standard to the primary standard, it must be standardized and compared.

To prepare the secondary standard solution, an aqueous solution of high purity must be used. Water must be deionized when used as an aqueous solvent. Standard solutions prepared without pure solvent are worthless (These points apply to primary standard solutions as well).

Similarly, individuals should check dates of manufacture, expiration dates, dates of receipt of high-grade chemicals, whether the conditions for their transport were followed or not, whether the seal has been damaged, its purity, and whether a standard reference material was used before using them.

Chemicals and reagents classified as secondary standards have certain properties, for instance
  1. Compared to the primary standard, it is less pure
  2. Stability and responsiveness are less than primary standards
  3. This solution, however, remains stable for quite some time
  4. A comparison has been made against primary standards
Chemicals that meet the requirements for being standard chemicals, but do not meet those of primary standards
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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