# Salkowski's test

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{{Short description|Qualitative chemical test, primarily used for detecting cholesterol}}
{{Infobox chemical analysis
| name           = Salkowski test
| image          = 
| caption        = 
| acronym        = 
| classification = Colorimetric method
| analytes       = Cholesterol, other sterols, indoles, terpenoids
| manufacturers  = 
| related        = 
| hyphenated     = 
}}
'''Salkowski's test''',<ref>{{Cite journal|last1=Rahman|first1=Atiqur|last2=Sitepu|first2=Irnayuli R.|last3=Tang|first3=Sui-Yan|last4=Hashidoko|first4=Yasuyuki|date=2010|title=Salkowski's reagent test as a primary screening index for functionalities of rhizobacteria isolated from wild dipterocarp saplings growing naturally on medium-strongly acidic tropical peat soil|journal=Bioscience, Biotechnology, and Biochemistry|volume=74|issue=11|pages=2202–2208|doi=10.1271/bbb.100360|issn=1347-6947|pmid=21071871|hdl=2115/45489|s2cid=12182924|hdl-access=free}}</ref> also known simply as '''Salkowski test''', is a [qualitative](/source/Qualitative_chemical_analysis) [chemical test](/source/chemical_test), that is used in chemistry and biochemistry for detecting a presence of [cholesterol](/source/cholesterol) and other [sterols](/source/Sterol).<ref name=":0">{{Cite web|title=Salkowski test for cholesterol - Its principle and procedure|url=https://medicalstudyzone.com/salkowski-test/|website=Medical Study Zone|date=2017-04-05|accessdate=2021-05-10|language=en-US}}</ref><ref>{{Cite web|title=Salkowski test|url=https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100438192|website=Oxford Reference|accessdate=2021-05-10|language=en}}</ref><ref>{{Cite journal|date=2012-01-14|title=Lipids1|url=https://www.slideshare.net/ariannarecio/lipids1|journal=|access-date=2021-05-10|magazine=}}</ref> This biochemical method got its name after German biochemist [Ernst Leopold Salkowski](/source/Ernst_Leopold_Salkowski),<ref name=":0" /> who is known for development of multiple new chemical tests, that are used for detection of different kinds of molecules (besides cholesterol and other sterols also for [creatinine](/source/creatinine), [carbon monoxide](/source/carbon_monoxide), [glucose](/source/glucose) and [indoles](/source/Indole)).<ref>{{Cite book|title=Dictionary of Medicine: French-English with English-French Glossary|url=https://books.google.com/books?id=Elx9GJ9qrtwC&q=Salkowski+indole+cholesterol+creatinine&pg=PA762|publisher=Schreiber Pub.|date=2004|isbn=978-1-887563-84-0|language=en|first1=Svetolik P.|last1=Djordjevic|first2=Svetolik P.|last2=Djordjević}}</ref> A solution that has tested positive on the Salkowski's test becomes red and gets yellow glow.<ref name=":1">{{Cite web|last1=Zahim|first1=Duaa|last2=Al-Saedi|first2=Dalal|title=General Biochemistry|url=https://www.kau.edu.sa/Files/0017586/Subjects/Bioc-371.pdf|accessdate=2021-05-10}}</ref>

== Basic information ==

=== Procedure ===
For Salkowski test's procedure one needs a sample, that is to be tested for sterols, as well as [chloroform](/source/chloroform) and concentrated [sulfuric acid](/source/sulfuric_acid) that represent Salkowski's reagent. Usually the solution of chloroform and  the sample is prepared first and later treated with concentrated sulfuric (VI) acid. After that the whole solution needs to be shaken well.<ref name=":0" /><ref name=":1" /> It is important to use only dried glassware, as [dehydration reaction](/source/dehydration_reaction) occurs during the test's procedure.<ref>{{Cite book|last=Sharma|first=D. C.|url=https://books.google.com/books?id=r4XVZUpIX5AC&q=salkowski+test&pg=PA17|title=Practical Medical Biochemistry|date=2007|publisher=BI Publications Pvt Ltd|isbn=978-81-7225-246-5|language=en}}</ref>

A solution that has tested positive on this qualitative chemical test exhibits two distinct layers in a test tube; the upper layer (chloroform) gets blueish red to violet colour, while the layer of sulfuric acid becomes yellow to green, with greenish glow being visible. If a sample does not contain any cholesterol or other sterols, colour of the tested solution remains unchanged and retains its original colour.<ref name=":0" /><ref>{{Cite web|title=Salkowski-Probe|url=https://medizin.de-academic.com/17496/Salkowski-Probe|website=Academic dictionaries and encyclopedias|accessdate=2021-05-10|language=de}}</ref><ref>{{Cite web|title=Salkowski test|url=https://www.chemwatch.net/resource-center/salkowski-test/|website=Chemwatch|accessdate=2021-05-10|language=en-US}}</ref>

Salkowski test can also be used to test the presence of [indoles](/source/Indole) (crystalline [alkaloid](/source/alkaloid)s that are a degradation products of proteins, containing [tryptophan](/source/tryptophan)<ref>{{Cite web|title=Definition of INDOLE|url=https://www.merriam-webster.com/dictionary/indole|website=www.merriam-webster.com|accessdate=2021-05-10|language=en}}</ref>). In such cases a sample is treated with [nitric acid](/source/nitric_acid) and 2% solution of [potassium nitrite](/source/potassium_nitrite), with positive reaction being shown by presence of red colour.<ref name=":2">{{Cite web|title=Salkowski test|url=https://medicine.en-academic.com/167413/Salkowski_test|website=Academic Dictionaries and Encyclopedias|language=en|accessdate=2021-05-10}}</ref>

=== Chemistry of the test ===
Treating a solution of a sample, containing sterols, with chloroform and highly [hygroscopic](/source/Hygroscopy) sulfuric acid, leads to a [dehydration reaction](/source/dehydration_reaction) (two water molecules are removed from two cholesterol molecules) and formation of new double bonds. During the chemical reaction two sterols bind together and bisterol (bisteroid) is formed; bi-[cholestadien](/source/Cholestadienes) (double [cholestene](/source/cholestene) with two double bonds) in a case of cholesterol. Red colour of a solution is a consequence of bi-[sulfonic acid](/source/sulfonic_acid) of a bi-cholestadien, which is a product of sulfuric acid [sulfonating](/source/Sulfonation) bi-cholestadien.<ref>{{Cite web|last=Selan|first=Karmen|date=2008|title=Vrednotenje izbranih kolorimetričnih metod za določanje koncentracije steroidov : diplomsko delo|url=https://repozitorij.uni-lj.si/IzpisGradiva.php?id=123070|access-date=2021-08-22|website=repozitorij.uni-lj.si}}</ref><ref>{{Cite web|title=How does Salkowski's Test for Steroid content work?|url=https://www.researchgate.net/post/How-does-Salkowskis-Test-for-Steroid-content-work|access-date=2021-08-22|website=ResearchGate|language=en}}</ref>

== References ==
{{Reflist}}
Category:Biochemistry detection methods
[https://medicalstudyhub.com/salkowski-test-for-cholesterol-its-principle-and-procedure/ Salkowski test for cholesterol – Its principle and procedure]

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