Article · Wikipedia archive · Last revised May 27, 2026

CAPS (buffer)

CAPS is the common name for 3-(Cyclohexylamino)-1-propanesulfonic acid, a compound used as a buffering agent in biochemistry. The similar substance N-cyclohexyl-2-hydroxyl-3-aminopropanesulfonic acid (CAPSO) is also used as buffering agent in biochemistry. Its useful pH range is 9.7-11.1. CAPS is a Good's buffer that is chemically stable and is commonly used in biochemical and analytical applications such as capillary electrophoresis.

Last revised
May 27, 2026
Read time
≈ 2 min
Length
511 w
Citations
6
Source
Wikipedia ↗
CAPS1
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Names
Preferred IUPAC name
3-(Cyclohexylamino)propane-1-sulfonic acid
Identifiers
3D model (JSmol)
ChemSpider
DrugBank
ECHA InfoCard 100.013.175
EC Number
  • 214-492-1
UNII
  • InChI=1S/C9H19NO3S/c11-14(12,13)8-4-7-10-9-5-2-1-3-6-9/h9-10H,1-8H2,(H,11,12,13) ☒N
    Key: PJWWRFATQTVXHA-UHFFFAOYSA-N ☒N
  • InChI=1/C9H19NO3S/c11-14(12,13)8-4-7-10-9-5-2-1-3-6-9/h9-10H,1-8H2,(H,11,12,13)
    Key: PJWWRFATQTVXHA-UHFFFAOYAU
  • C1CCC(CC1)NCCCS(=O)(=O)O
Properties
C9H19NO3S
Molar mass 221.32 g/mol
Melting point >300 °C
Acidity (pKa) 10.42
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H302, H315, H319, H335
P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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CAPS is the common name for 3-(Cyclohexylamino)-1-propanesulfonic acid, a compound used as a buffering agent in biochemistry. The similar substance N-cyclohexyl-2-hydroxyl-3-aminopropanesulfonic acid (CAPSO) is also used as buffering agent in biochemistry. Its useful pH range is 9.7-11.1. CAPS is a Good's buffer that is chemically stable and is commonly used in biochemical and analytical applications such as capillary electrophoresis.3

Chemical Properties

CAPS is one of Good's buffers, a class of zwitterionic buffers widely used in biochemical research. These buffers are designed to be chemically inert, non-toxic, weakly chelating, and relatively stable across temperature changes. CAPS is highly soluble in water but exhibits low solubility in organic solvents, due to its high polarity.4

Chemical Reactivity and Applications

Compared to several other Good's buffers, CAPS shows different behavior in metal-catalyzed oxidation systems. Many Good's buffers will readily form nitrogen-centered free radicals in the presence of Au(III) at neutral pH, leading to the cleavage of DNA. CAPS, under the same conditions, does not produce detectable free radicals or induce DNA cleavage.5

CAPS is used in capillary electrophoresis for the determination of pKa values for compounds that ionize at high pH. This includes weakly basic and weakly acidic compounds, such as amines and phenols. Its effectiveness arises from its minimal interaction with analytes reducing interference and allowing measurements to more accurately reflect the analyte.3

See also

See also

References

References

  1. CAPS at Sigma-Aldrich
  2. Esplin, Taran L.; Cable, Morgan L.; Gray, Harry B.; Ponce, Adrian (2010). "Terbium-Macrocycle Complexes as Chemical Sensors: Detection of an Aspirin Metabolite in Urine Using a Salicylurate-Specific Receptor Site". Inorganic Chemistry. 49 (10): 4643–4647. doi:10.1021/ic1003066.
    Tabata, Masaaki; Habib, Ahsan; Watanabe, Keiichi (2005). "DNA Cleavage by Good's Buffers in the Presence of Au(III)". Bulletin of the Chemical Society of Japan. 78 (7): 1263–1269. doi:10.1246/bcsj.78.1263.
  3. Fuguet, Elisabet; Reta, Mario; Gibert, Carme; Rosés, Martí; Bosch, Elisabeth; Ràfols, Clara (July 8, 2008). "Critical evaluation of buffering solutions for p K a determination by capillary electrophoresis". ELECTROPHORESIS. 29 (13): 2841–2851. doi:10.1002/elps.200700869. ISSN 0173-0835.
  4. Taha, Mohamed; Coutinho, João A.P. (June 5, 2016). "Organic-phase biological buffers for biochemical and biological research in organic media". Journal of Molecular Liquids. 221: 197–205. doi:10.1016/j.molliq.2016.05.052.
  5. Tabata, Masaaki; Habib, Ahsan; Watanabe, Keiichi (2005-07-01). "DNA Cleavage by Good's Buffers in the Presence of Au(III)". Bulletin of the Chemical Society of Japan. 78 (7): 1263–1269. doi:10.1246/bcsj.78.1263. ISSN 0009-2673.