# Spot analysis

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{{Short description|Chemical test}}
'''Spot analysis''', '''spot test analysis''', or a '''spot test''' is a [chemical test](/source/chemical_test), a simple and efficient technique where analytic assays are executed in only one, or a few drops, of a chemical solution, preferably in a great piece of filter paper, without using any sophisticated instrumentation. The development and popularization of the test is credited to [Fritz Feigl](/source/Fritz_Feigl).<ref>[https://books.google.com/books/about/Spot_tests_in_organic_analysis.html?id=nK7QAAAAMAAJ "Spot tests in organic analysis"], numerous editions</ref><ref name=bull>{{cite journal|url = http://www.scs.illinois.edu/~mainzv/HIST/bulletin_open_access/num17-18/num17-18%20p31-39.pdf|title = Fritz Feigl (1891-1971): The Centennial of a Researcher|first1 = Aida|last1 = Espinola|first2 = Mario A.|last2 = da Silva Pinto|first3 = Claudio|last3 = Costa Neto|journal = [Bull. Hist. Chem.](/source/Bull._Hist._Chem.)|volume = 17/18|year = 1995|pages = 31–39}}</ref>

'''Spot test''' or '''spot assay''' can also refer to a test often used in microbiology.

==Chemistry==
The foundations of Feigl's work on spot analysis were the works of [Hugo Schiff](/source/Hugo_Schiff) (the earliest publication about "spot test" was Shiff's detection of [uric acid](/source/uric_acid) in 1859<ref>H. Schiff, ''[Ann. Chim. Acta](/source/Ann._Chim._Acta)'', 1859, 109, 67.</ref>) and of [Christian Friedrich Schonberg](/source/Christian_Friedrich_Schonberg) and [Friedrich Goppelsröder](/source/Friedrich_Goppelsr%C3%B6der) on [capillary analysis](/source/capillary_analysis).<ref name=bull/>

On the occasion of Feigl's 70th birthday the [Chemical Society of Midland](/source/Chemical_Society_of_Midland) sponsored a symposium in 1952, attended by 500 scientists from 24 countries, in which all plenary sessions were related to spot tests.<ref name=bull/>

The test uses the qualitative characteristics of colored compounds to account for performed chemical reactions. This technique has been used to develop new quantification methods using modern technology.<ref>{{cite journal|last1=Soares|first1=Samara|last2=Lima|first2=Manoel J.A.|last3=Rocha|first3=Fábio R.P.|title=A spot test for iodine value determination in biodiesel based on digital images exploiting a smartphone|journal=Microchemical Journal|volume=133|pages=195–199|doi=10.1016/j.microc.2017.03.029|year=2017}}</ref>

==Microbiology==
[[File:Spot assay yeast cells.jpg|thumb|Spot assay of [yeast](/source/yeast) cells on an [agar plate](/source/agar_plate). The spots show either growth (cells) or no growth (no cells)]]
thumb|96 pinner used to perform spot assays with yeast or bacterial cells
A spot assay or spot test can also refer to a specific test in microbiology. This test is often used to check the growth rate of bacterial or yeast cells on different media or to perform serial dilution tests of micro-organisms. Usually a 96-pinner (often called frogger) is used to perform these spot assay.
Another application is [high-throughput screening](/source/high-throughput_screening), whichoften uses spot assays to determine the growth of eg. mated cells or to check for [protein-protein interactions](/source/Protein%E2%80%93protein_interaction) in a yeast [two-hybrid test](/source/Two-hybrid_screening). This is often done with a robot.<ref name="Thomas">{{cite journal|last1 = Thomas|first1 = Pious|last2 = Shekhar|first2 = Aparna C.|last3 = Upreti|first3 = Reshmi|last4 = Mujawar|first4 = Mohammad M.|last5 = Pasha|first5 = Sadiq S.|title = Optimization of single plate-serial dilution spotting (SP-SDS) with sample anchoring as an assured method for bacterial and yeast cfu enumeration and single colony isolation from diverse samples|journal = [Biotechnology Reports](/source/Biotechnology_Reports)|volume = 8|pages = 45–55|year = 2015|pmid = 28352572|doi = 10.1016/j.btre.2015.08.003|pmc=4980700}}</ref>

==See also==
*[Spot test (lichen)](/source/Spot_test_(lichen))
*[Touchstone](/source/Touchstone_(assaying_tool))

==References==
{{Reflist}}

{{Authority control}}

Category:Chemical tests
Category:Analytical chemistry
Category:Measurement
Category:Brazilian inventions

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