# Reagent

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Substance added to a system to cause a chemical reaction

"Reactants" redirects here; not to be confused with [Reactance](/source/Reactance_(disambiguation)) or [Regent](/source/Regent).

Reagents, such as [sulfur](/source/Sulfur) (pictured), are the starting materials used in chemical reactions.

In [chemistry](/source/Chemistry), a **reagent** ([/riˈeɪdʒənt/](https://en.wikipedia.org/wiki/Help:IPA/English) [*ree-AY-jənt*](https://en.wikipedia.org/wiki/Help:Pronunciation_respelling_key)) or **analytical reagent** is a substance or [compound](/source/Compound_(chemistry)) added to a system to cause a [chemical reaction](/source/Chemical_reaction), or test if one occurs.[1] A **reactant** is a substance or compound that is consumed in a chemical reaction.[1] The terms *reactant* and *reagent* are often used interchangeably, but reactant specifies a substance *consumed* in the course of a chemical reaction; *reagent* is used in the context of [chemical analysis](/source/Chemical_analysis), while *reactant* is used in the context of reaction itself. [Solvents](/source/Solvent), though involved in the [reaction mechanism](/source/Reaction_mechanism), are usually not called reactants. Similarly, *[catalysts](/source/Catalysis)* are not consumed by the reaction, so they are not reactants. In [biochemistry](/source/Biochemistry), especially in connection with [enzyme](/source/Enzyme)-catalyzed reactions, the reactants are commonly called [substrates](/source/Substrate_(biochemistry)).

## Definitions

### Organic chemistry

In [organic chemistry](/source/Organic_chemistry), the term "reagent" denotes a chemical ingredient (a compound or mixture, typically of inorganic or small organic molecules) introduced to cause the desired transformation of an organic substance. Examples include the [Collins reagent](/source/Collins_reagent), [Fenton's reagent](/source/Fenton's_reagent), and [Grignard reagents](/source/Grignard_reagent).[2]

### Analytical chemistry

In [analytical chemistry](/source/Analytical_chemistry), a reagent is a compound or mixture used to detect the presence or absence of another substance, e.g. by a color change, or to measure the concentration of a substance, e.g. by [colorimetry](/source/Colorimetry_(chemical_method)). Examples include [Fehling's reagent](/source/Fehling's_reagent), [Millon's reagent](/source/Millon's_reagent), and [Tollens' reagent](/source/Tollens'_reagent).[3]

## Commercial or laboratory preparations

In commercial or laboratory preparations, **[reagent-grade](/source/Chemical_purity)** designates [chemical substances](/source/Chemical_substance) meeting [standards](/source/Standardization) of [purity](/source/Purity_(gas)) that ensure the scientific precision and reliability of [chemical analysis](/source/Chemical_analysis), chemical reactions or physical testing. Purity standards for reagents are set by organizations such as [ASTM International](/source/ASTM_International) or the [American Chemical Society](/source/American_Chemical_Society). For instance, reagent-quality water must have very low levels of impurities such as [sodium](/source/Sodium) and [chloride](/source/Chloride) ions, [silica](/source/Silica), and bacteria, as well as a very high [electrical resistivity](/source/Electrical_resistivity). Laboratory products which are *less* pure, but still useful and economical for undemanding work, may be designated as *technical*, *practical*, or *crude* grade to distinguish them from reagent versions.[4]

## Biology

In the field of biology, the [biotechnology](/source/Biotechnology) revolution in the 1980s grew from the development of reagents that could be used to identify and manipulate the chemical matter in and on cells.[5][6] These reagents included [antibodies](/source/Antibody#Research_applications) ([polyclonal](/source/Polyclonal_antibodies) and [monoclonal](/source/Monoclonal_antibody)), [oligomers](/source/Oligomers), all sorts of [model organisms](/source/Model_organisms) and [immortalised cell lines](/source/Immortalised_cell_line), reagents and methods for [molecular cloning](/source/Molecular_cloning) and [DNA replication](/source/DNA_replication), and many others.[6][7]

### Tool compounds

Tool compounds are an important class of reagent in biology. They are small molecules or biochemicals like [siRNA](/source/SiRNA) or antibodies that are known to directly interact with or modulate a specific biomolecule—for example a [drug target](/source/Drug_target)—but are unlikely to be useful as drugs themselves, and are often starting points in the [drug discovery](/source/Drug_discovery) process.[8][9]

However, many natural substances are hits in almost any assay in which they are tested, and therefore not useful as tool compounds. Medicinal chemists class them instead as [pan-assay interference compounds](/source/Pan-assay_interference_compounds). One example is [curcumin](/source/Curcumin).[10][11][12]

## See also

- [Limiting reagent](/source/Limiting_reagent)

- [Common reagents](/source/List_of_reagents)

- [Product](/source/Product_(chemistry))

- [Reagent bottle](/source/Reagent_bottle)

- [Substrate](/source/Substrate_(chemistry))

- [All pages with titles containing *Reagent*](https://en.wikipedia.org/wiki/Special:Search/intitle:%22Reagent%22)

## References

1. ^ [***a***](#cite_ref-gold_1-0) [***b***](#cite_ref-gold_1-1) [IUPAC](/source/International_Union_of_Pure_and_Applied_Chemistry), *[Compendium of Chemical Terminology](/source/IUPAC_books#Gold_Book)*, 5th ed. (the "Gold Book") (2025). Online version: (1996) "[Reactant](https://goldbook.iupac.org/terms/view/R05163.html)". [doi](/source/Doi_(identifier)):[10.1351/goldbook.R05163](https://doi.org/10.1351%2Fgoldbook.R05163)

1. **[^](#cite_ref-2)** ["Common Reagents in Organic Chemistry"](https://commonorganicchemistry.com/Sidebar/Common_Reagents.htm). CommonOrganicChemistry.com. Retrieved 9 March 2026.

1. **[^](#cite_ref-3)** ["Analytical Reagents - Analytical Products / Alfa Chemistry"](https://reagents.alfa-chemistry.com/products/analytical-reagents.html?srsltid=AfmBOoq2MOEQ3AdLVOiUlD3AtVDjxDWSPwcKVt-TzrWCBGxY0mKqhh6E). Alfa Chemistry. Retrieved 9 March 2026.

1. **[^](#cite_ref-4)** ["Preparing Chemical Solutions, Reagents, and Buffers"](https://wp.stolaf.edu/chemical-hygiene/preparing-chemical-solutions-reagents-and-buffers/#:~:text=The%20ability%20to%20prepare%20accurate%20laboratory%20reagents,Calculator**%20Dilutes%20a%20solution%20of%20known%20molarity). St. Olaf College. Retrieved 9 March 2026.

1. **[^](#cite_ref-5)** Fox, Jeffrey L (1 January 1979). "Antibody reagents revolutionizing immunology". *Chemical & Engineering News Archive*. **57**: 15–17. [doi](/source/Doi_(identifier)):[10.1021/cen-v057n001.p015](https://doi.org/10.1021%2Fcen-v057n001.p015).

1. ^ [***a***](#cite_ref-NIHreport1998_6-0) [***b***](#cite_ref-NIHreport1998_6-1) ["Report of the National Institutes of Health (NIH) Working Group on Research Tools"](https://web.archive.org/web/20000816014021/http://www.nih.gov/news/researchtools/index.htm). NIH. June 4, 1998. Archived from [the original](http://www.nih.gov/news/researchtools/index.htm) on August 16, 2000.

1. **[^](#cite_ref-7)** Ishino, S; Ishino, Y (29 August 2014). ["DNA polymerases as useful reagents for biotechnology: the history of developmental research in the field"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4148896). *Frontiers in Microbiology*. **5**: 465. [doi](/source/Doi_(identifier)):[10.3389/fmicb.2014.00465](https://doi.org/10.3389%2Ffmicb.2014.00465). [PMC](/source/PMC_(identifier)) [4148896](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4148896). [PMID](/source/PMID_(identifier)) [25221550](https://pubmed.ncbi.nlm.nih.gov/25221550).

1. **[^](#cite_ref-8)** Kenakin, T; Bylund, DB; Toews, ML; Mullane, K; Winquist, RJ; Williams, M (1 January 2014). "Replicated, replicable and relevant-target engagement and pharmacological experimentation in the 21st century". *Biochemical Pharmacology*. **87** (1): 64–77. [doi](/source/Doi_(identifier)):[10.1016/j.bcp.2013.10.024](https://doi.org/10.1016%2Fj.bcp.2013.10.024). [PMID](/source/PMID_(identifier)) [24269285](https://pubmed.ncbi.nlm.nih.gov/24269285).

1. **[^](#cite_ref-9)** Lindsley, CW (25 September 2014). ["2013 Philip S. Portoghese Medicinal Chemistry Lectureship: drug discovery targeting allosteric sites"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4174999). *Journal of Medicinal Chemistry*. **57** (18): 7485–7498. [doi](/source/Doi_(identifier)):[10.1021/jm5011786](https://doi.org/10.1021%2Fjm5011786). [PMC](/source/PMC_(identifier)) [4174999](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4174999). [PMID](/source/PMID_(identifier)) [25180768](https://pubmed.ncbi.nlm.nih.gov/25180768).

1. **[^](#cite_ref-10)** Baker, Monya (9 January 2017). ["Deceptive curcumin offers cautionary tale for chemists"](https://doi.org/10.1038%2F541144a). *Nature*. **541** (7636): 144–145. [Bibcode](/source/Bibcode_(identifier)):[2017Natur.541..144B](https://ui.adsabs.harvard.edu/abs/2017Natur.541..144B). [doi](/source/Doi_(identifier)):[10.1038/541144a](https://doi.org/10.1038%2F541144a). [PMID](/source/PMID_(identifier)) [28079090](https://pubmed.ncbi.nlm.nih.gov/28079090).

1. **[^](#cite_ref-11)** Dahlin, JL; Walters, MA (July 2014). ["The essential roles of chemistry in high-throughput screening triage"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465542). *[Future Medicinal Chemistry](/source/Future_Medicinal_Chemistry)*. **6** (11): 1265–1290. [doi](/source/Doi_(identifier)):[10.4155/fmc.14.60](https://doi.org/10.4155%2Ffmc.14.60). [PMC](/source/PMC_(identifier)) [4465542](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465542). [PMID](/source/PMID_(identifier)) [25163000](https://pubmed.ncbi.nlm.nih.gov/25163000).

1. **[^](#cite_ref-12)** Baell, JB; Holloway, GA (8 April 2010). "New substructure filters for removal of pan assay interference compounds (PAINS) from screening libraries and for their exclusion in bioassays". *Journal of Medicinal Chemistry*. **53** (7): 2719–2740. [CiteSeerX](/source/CiteSeerX_(identifier)) [10.1.1.394.9155](https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.394.9155). [doi](/source/Doi_(identifier)):[10.1021/jm901137j](https://doi.org/10.1021%2Fjm901137j). [PMID](/source/PMID_(identifier)) [20131845](https://pubmed.ncbi.nlm.nih.gov/20131845).

## External links

- Media related to [Reagents](https://commons.wikimedia.org/wiki/Category:Reagents) at Wikimedia Commons

- The dictionary definition of [*reactant*](https://en.wiktionary.org/wiki/reagent) at Wiktionary

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Adapted from the Wikipedia article [Reagent](https://en.wikipedia.org/wiki/Reagent) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Reagent?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.