What Is a Reagent? Definition and Examples

Reagent vs Reactant
A reagent is added to a cause a reaction or test if one occurred, while a reactant is a starting material in a reaction that is consumed to make the product.

A reagent is a substance added to a system to cause a chemical reaction, test whether one occurred, or test for a specific chemical.

Reagent Examples

A reagent may be a compound, mixture, or solution. In organic chemistry, more reagents are inorganic compounds or small organic molecules. In biotechnology, reagents include monoclonal and polyclonal antibodies, oligomers, and cell lines. In analytical chemistry, reagents are often indicators that change color to confirm the presence or absence of another chemical. Examples of named reagents include Grignard reagent, Tollens’ reagent, Fehling’s reagent, Millon’s reagent, Collins reagent, and Fenton’s reagent. But, not all reagents have the word “reagent” in their name. Solvents, enzymes, and catalysts are also examples of reagents.

Reagent vs Reactant

In older literature, the terms “reactant” and “reagent” often were used interchangeably. However, the two terms don’t mean the same thing today. A reactant is a starting material for a chemical reaction that is consumed to make one or more products. A reagent isn’t necessarily consumed in a reaction.

What Reagent-Grade Means

Suppliers may identify chemicals as “reagent-grade” or “reagent-quality.” What this means is that the substance is pure enough to be used for chemical analysis or physical testing. The American Chemical Society (ACS) and American Society for Testing and Materials (ASTM) are among the organizations that set the purity levels for labeling a product as reagent-grade. Typically, reagent-grade chemicals are free of contaminants that affect common tests. For example, reagent-grade water contains low impurity levels of bacteria, sodium and chlorine ions, and silica. Chemicals that are not reagent-grade may be called crude, practical, or technical grade. Lower purity chemicals are more economical and useful for most applications, but if a protocol specifies reagent-grade there’s probably a good reason. Which grade you choose depends on the nature of the work being performed.


  • Fox, Jeffrey L. (1 January 1979). “Antibody reagents revolutionizing immunology”. Chemical & Engineering News Archive. pp. 15–17. doi:10.1021/cen-v057n001.p015
  • Ishino, S.; Ishino, Y. (August 2014). “DNA polymerases as useful reagents for biotechnology: the history of developmental research in the field”. Frontiers in Microbiology5: 465. doi:10.3389/fmicb.2014.00465
  • IUPAC (1997). “Reactant”. Compendium of Chemical Terminology (the “Gold Book”) (2nd ed.). Oxford: Blackwell Scientific Publications. ISBN:0-9678550-9-8. doi:10.1351/goldbook