Editing Ninhydrin

{{Use dmy dates|date=February 2023}}
{{chembox
| Watchedfields = changed
| verifiedrevid = 412692887
| Name = Ninhydrin
| ImageFile = Ninhydrin.svg
| ImageFile1 = 
| ImageSize = 
| ImageName = Ninhydrin
| ImageFile2 = Ninhydrin sample.jpg
| ImageSize2 = 300px
| PIN = 2,2-Dihydroxy-1''H''-indene-1,3(2''H'')-dione
| OtherNames = 2,2-Dihydroxyindane-1,3-dione<br />1,2,3-Indantrione hydrate
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 485-47-2
| PubChem = 10236
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 1221925
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 9819
| EC_number = 213-340-1
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = HCL6S9K23A
| InChI = 1/C9H6O4/c10-7-5-3-1-2-4-6(5)8(11)9(7,12)13/h1-4,12-13H
| InChIKey = FEMOMIGRRWSMCU-UHFFFAOYAM
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C9H6O4/c10-7-5-3-1-2-4-6(5)8(11)9(7,12)13/h1-4,12-13H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = FEMOMIGRRWSMCU-UHFFFAOYSA-N
| SMILES = O=C2c1ccccc1C(=O)C2(O)O
 }}
|Section2={{Chembox Properties
| C=9 | H=6 | O=4
| Formula = C<sub>9</sub>H<sub>6</sub>O<sub>4</sub>
| Appearance = White solid
| Density = 0.862 g/cm<sup>3</sup>
| Solubility = 20 g L<sup>−1</sup><ref name=merck>''Chemicals and reagents'', 2008–2010, Merck</ref>
| MeltingPtC = 250
| MeltingPt_notes = (decomposes)
| BoilingPt = 
 }}
|Section7={{Chembox Hazards
| GHSPictograms = {{GHS07}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|302|315|319|335}}
| PPhrases = {{P-phrases|261|264|270|271|280|301+312|302+352|304+340|305+351+338|312|321|330|332+313|337+313|362|403+233|405|501}}
| ExternalSDS = [http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=US&language=en&productNumber=151173&brand=SIAL&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fsearch%3Fterm%3DNinhydrin%26interface%3DAll%26N%3D0%26mode%3Dmatch%2520partialmax%26lang%3Den%26region%3DUS%26focus%3Dproduct External MSDS]
 }}
}}

'''Ninhydrin''' (2,2-dihydroxyindane-1,3-dione) is an [[organic compound]] with the formula C<sub>6</sub>H<sub>4</sub>(CO)<sub>2</sub>C(OH)<sub>2</sub>.  It is used to detect [[ammonia]] and [[amine]]s. Upon reaction with these amines, ninhydrin gets converted into deep blue or purple derivatives, which are called Ruhemann's purple. Ninhydrin is most commonly used to detect [[fingerprint]]s in [[forensic science|forensic]] cases, as the terminal [[amine]]s of [[lysine]] residues in [[Peptide|peptides]] and [[Protein|proteins]] sloughed off in fingerprints react with ninhydrin.<ref>{{cite web|archive-url=https://web.archive.org/web/20070613175807/http://www.bergen.org/EST/Year5/fingerprint.htm|archive-date=13 June 2007|title=Fingerprinting Analysis|publisher=Bergen County Technical Schools|url=http://www.bergen.org/EST/Year5/fingerprint.htm|date=June 2003|url-status=dead}}</ref><ref>{{cite book |doi=10.1002/0471238961.0615180506091908.a01.pub3|chapter=Forensic Chemistry|title=Kirk-Othmer Encyclopedia of Chemical Technology|year=2015|last1=Rowe|first1=Walter F.|pages=1–19|isbn=9780471238966}}</ref>

Ninhydrin is a white solid that is soluble in [[ethanol]] and [[acetone]].<ref name=merck/> Ninhydrin can be considered as the [[hydrate]] of [[indane-1,2,3-trione]].

== History ==
Ninhydrin was discovered in 1910 by the German-English chemist Siegfried Ruhemann (1859–1943).<ref>{{cite journal|author=Ruhemann, Siegfried |year=1910|url=https://archive.org/stream/p2journal97chemuoft#page/1438/mode/2up |title=Cyclic Di- and Tri-ketones|journal=Journal of the Chemical Society, Transactions|volume=97|pages= 1438–1449|doi=10.1039/ct9109701438}}</ref><ref>{{cite journal |author=West, Robert |date=1 July 1965 |title=Siegfried Ruhemann and the Discovery of Ninhydrin |url=https://pubs.acs.org/doi/abs/10.1021/ed042p386 |journal=Journal of Chemical Education |volume=42 |issue=7 |pages=386–388 |bibcode=1965JChEd..42..386W |doi=10.1021/ed042p386|url-access=subscription }}</ref> In the same year, Ruhemann observed ninhydrin's reaction with [[Amino acid|amino acids]].<ref>{{cite journal|author=Ruhemann, S. |year=1910|url=https://archive.org/stream/p2journal97chemuoft#page/2024/mode/2up |title=Triketohydrindene Hydrate|journal=Journal of the Chemical Society, Transactions|volume=97|pages=2025–2031|doi=10.1039/ct9109702025}}</ref> In 1954, Swedish investigators Oden and von Hofsten proposed that ninhydrin could be used to develop latent fingerprints.<ref>{{cite journal|author1=Odén, Svante|author2=von Hofsten, Bengt|name-list-style=amp|year= 1954|title=Detection of Fingerprints by the Ninhydrin Reaction|url=https://ui.adsabs.harvard.edu/abs/1954Natur.173..449O/abstract|doi=10.1038/173449a0|pmid= 13144778|journal=Nature|volume=173|issue=4401|pages= 449–450|bibcode=1954Natur.173..449O |s2cid=4187222}}</ref><ref>{{cite web|last1=Oden|first1=Svante.|url=http://pdfpiw.uspto.gov/.piw?Docid=02715571&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect2%3DPTO1%2526Sect2%3DHITOFF%2526p%3D1%2526u%3D%2Fnetahtml%2FPTO%2Fsearch-bool.html%2526r%3D1%2526f%3DG%2526l%3D50%2526d%3DPALL%2526S1%3D2715571.PN.%2526OS%3DPN%2F2715571%2526RS%3DPN%2F2715571&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page|title=Process of Developing Fingerprints}} U.S. Patent no. 2,715,571 (filed:  27 September 1954; issued:  16 August 1955).</ref>

==Uses==
Ninhydrin can be used in Kaiser test to monitor [[deprotection]] in [[solid phase peptide synthesis]].<ref>{{cite journal|doi=10.1016/0003-2697(70)90146-6|title=Color Test for Detection of Free Terminal Amino Groups in the Solid-Phase Synthesis of Peptides |journal=Analytical Biochemistry|volume= 34|issue=2 |year=1970|last1=Kaiser |first1=E. |last2=Colescott |first2=R.L. |last3=Bossinger |first3=C.D. |last4=Cook |first4=P.I. |pages=595–8 |pmid=5443684 }}</ref> The chain is linked via its [[C-terminus]] to the solid support, with the [[N-terminus]] extending off it. When that nitrogen is deprotected, a ninhydrin test yields blue. Amino-acid residues are attached with their N-terminus protected, so if the next residue has been successfully coupled onto the chain, the test gives a colorless or yellow result.

Ninhydrin is also used in [[Qualitative inorganic analysis|qualitative analysis]] of proteins. Most of the amino acids, except [[proline]], are [[hydrolysis|hydrolyzed]] and react with ninhydrin. Also, certain amino acid chains are degraded. Therefore, separate analysis is required for identifying such amino acids that either react differently or do not react with ninhydrin at all. The rest of the amino acids are then quantified colorimetrically after separation by [[chromatography]].

A solution suspected of containing the [[ammonium]] ion can be tested by ninhydrin by dotting it onto a solid support (such as [[silica gel]]); treatment with ninhydrin should result in a dramatic purple color if the solution contains this species. In the analysis of a chemical reaction by [[thin layer chromatography]] (TLC), the reagent can also be used (usually 0.2% solution in either n-butanol or in ethanol). It will detect, on the TLC plate, virtually all [[amine]]s, [[carbamate]]s and also, after vigorous heating, [[amide]]s.

Upon reaction with ninhydrin, amino acids undergo [[decarboxylation]].  The released CO<sub>2</sub> originates from the carboxyl carbon of the amino acid. This reaction has been used to release the carboxyl carbons of bone [[collagen]] from ancient bones<ref>{{cite journal|author1=Keeling, C. I. |author2=Nelson, D. E. |author3=Slessor, K. N.  |name-list-style=amp |journal=Archaeometry|volume= 41 |pages=151–164 |year=1999|doi=10.1111/j.1475-4754.1999.tb00857.x|title=Stable Carbon Isotope Measurements of the Carboxyl Carbons in Bone Collagen|url=http://summit.sfu.ca/system/files/iritems1/6994/b17944776.pdf}}</ref> for stable [[isotope analysis]] in order to help reconstruct the palaeodiet of [[cave bears]].<ref>{{cite journal|author1=Keeling, C. I. |author2=Nelson, D. E. |journal=Oecologia|volume= 127|issue=4|pages=495–500|year=2001|jstor=4222957|doi=10.1007/S004420000611|title=Changes in the Intramolecular Stable Carbon Isotope Ratios with Age of the European Cave Bear (''Ursus spelaeus'')|pmid=28547486 |bibcode=2001Oecol.127..495K |s2cid=23508811 }}</ref> Release of the carboxyl carbon (via ninhydrin) from amino acids recovered from soil that has been treated with a labeled substrate demonstrates assimilation of that substrate into microbial protein.<ref>{{cite journal|author=Marsh, K. L., Mulvaney, R. L. and Sims, G. K. |year=2003|title= A Technique to Recover Tracer as Carboxyl-Carbon and α-Nitrogen from Amino Acids in Soil Hydrolysates|journal= J. AOAC Int.|pmid=14979690|volume= 86|issue=6|pages=1106–1111|doi=10.1093/jaoac/86.6.1106|doi-access=free}}</ref> This approach was successfully used to reveal that some ammonium oxidizing bacteria, also called [[nitrifying bacteria]] use [[urea]] as a carbon source in soil.<ref>{{cite journal|author=Marsh, K. L., Sims, G. K. and Mulvaney, R. L. |year= 2005|title= Availability of Urea to Autotrophic Ammonia-Oxidizing Bacteria as Related to the Fate of <sup>14</sup>C- and <sup>15</sup>N-labeled Urea Added to Soil|journal= Biol. Fert. Soil.|volume= 42|issue= 2|pages=137–145|doi=10.1007/s00374-005-0004-2|bibcode= 2005BioFS..42..137M|s2cid= 6245255}}</ref>

[[File:Ninhydrin staining thumbprint.png|right|thumb|A stain obtained after a thumbprint is treated with ninhydrin.]]

===Forensics===
A ninhydrin solution is commonly used by [[forensic investigator]]s in the analysis of [[latent fingerprint]]s on [[porous]] surfaces such as paper. The [[amino acid]]s present in the minute sweat secretions that gather on the finger's unique ridges transfer to surfaces that are touched. Exposure of the surface to ninhydrin converts the amino acids into visibly colored products and thus reveals the print.<ref>Menzel, E.R. (1986) ''Manual of fingerprint development techniques''. Home Office, Scientific Research and Development Branch, London. {{ISBN|0862522307}}</ref> The test solutions suffer from poor long-term stability, especially if not kept cold.<ref>{{Cite journal|last1=Janssen-Bouwmeester|first1=Roy|last2=Bremmer|first2=Christiaan|last3=Koomen|first3=Linda|last4=Siem-Gorré|first4=Shermayne|last5=de Puit|first5=Marcel|date=May 2020|title=Positive control tests for fingermark development reagents|journal=Forensic Science International|language=en|volume=310|pages=110259|doi=10.1016/j.forsciint.2020.110259|pmid=32224429|s2cid=214732288}}</ref>

To further enhance the ability of ninhydrin, a solution of [[1,2-indandione]] and [[zinc chloride]] (IND-Zn) can be used prior to ninhydrin. This sequence leads to greater overall reaction of the amino acids, possibly by IND-Zn helping to release them from the surface for the subsequent ninhydrin reaction.<ref>{{Cite journal|last1=Mangle|first1=Milery Figuera|last2=Xu|first2=Xioama|last3=de Puit|first3=M.|date=September 2015|title=Performance of 1,2-indanedione and the need for sequential treatment of fingerprints|journal=Science & Justice|language=en|volume=55|issue=5|pages=343–346|doi=10.1016/j.scijus.2015.04.002|pmid=26385717}}</ref>

==Reactivity==
Ninhydrin exists in equilibrium with the triketone [[indane-1,2,3-trione]], which reacts readily with nucleophiles (including water). Whereas for most carbonyl compounds, a carbonyl form is more stable than a product of water addition (hydrate), ninhydrin forms a stable hydrate of the central carbon because of the destabilizing effect of the adjacent carbonyl groups.

To generate the ninhydrin [[chromophore]] [2-(1,3-dioxoindan-2-yl)iminoindane-1,3-dione], the amine must condense to give a [[Schiff base]]. The reaction of ninhydrin with secondary amines gives an iminium salt, which is also coloured, generally being yellow–orange.

:[[File:Ninhydrin Reaction Mechanism.svg|450px]]

==Effects on health==
Ninhydrin may cause allergic, IgE-mediated rhinitis and asthma.<ref name="Piirilä_1997" >{{cite journal | vauthors = Piirilä P, Estlander T, Hytönen M, Keskinen H, Tupasela O, Tuppurainen M| title = Rhinitis caused by ninhydrin develops into occupational asthma | journal = Eur Respir J | volume = 10 | issue = 8 | pages = 1918–1921| date = August 1997 | doi =10.1183/09031936.97.10081918 |pmid = 9272939 | doi-access = free }}</ref> A case has been described in which a 41 year old forensic laboratory worker working with Ninhydrin developed rhinitis and respiratory difficulty. Her specific IgE levels were found almost doubled.<ref name="Piirilä_1997"/>

==See also==
{{Commons category}}
* [[Hydrindantin]]
* [[Paper chromatography]]

==References==
{{reflist}}

[[Category:Chemical tests]]
[[Category:Reagents for organic chemistry]]
[[Category:Forensic chemicals]]
[[Category:Geminal diols]]
[[Category:1,3-Indandiones]]
[[Category:Protein dyes]]