Editing There are unknown unknowns (section)

==Analytical sciences==
The term "known unknowns" has been applied to the identification of chemical substances using [[analytical chemistry]] approaches, specifically [[mass spectrometry]]. In many cases, an unknown to an investigator that is detected in an experiment is actually known in the chemical literature, a reference database, or an Internet resource. These types of compounds are termed "known unknowns". The term was originally coined by Little et al.<ref>{{cite journal |last1=Little |first1=J.L. |last2=Cleven |first2=C.D. |last3=Brown |first3=S.D. |year=2011 |title=Identification of "Known Unknowns" utilizing accurate mass data and chemical abstracts service databases |journal=J. Am. Soc. Mass Spectrom. |volume=22 |issue=2 |pages=348–359 |doi=10.1007/s13361-010-0034-3 |pmid=21472594 |bibcode=2011JASMS..22..348L |doi-access=free }}</ref> and reported a number of times in the literature since then as a general approach.<ref>{{cite journal |title=Identification of "known unknowns" utilizing accurate mass data and ChemSpider |doi=10.1007/s13361-011-0265-y |pmid=22069037 |volume=23 |issue=1 |journal=Journal of the American Society for Mass Spectrometry |pages=179–185 |year=2011 |last1=Little |first1=James L. |doi-access=free }}</ref><ref>{{cite journal |last1=Stein |first1=S. |year=2012 |title=Mass Spectral Reference Libraries: An Ever-Expanding Resource for Chemical Identification |journal=Analytical Chemistry |volume=84 |issue=17 |pages=7274–7282 |doi=10.1021/ac301205z |pmid=22803687 }}</ref><ref>{{cite journal |title=Identifying known unknowns using the US EPA's CompTox Chemistry Dashboard |doi=10.1007/s00216-016-0139-z |pmid=27987027 |volume=409 |issue=7 |journal=Analytical and Bioanalytical Chemistry |pages=1729–1735 |year=2016 |last1=McEachran |first1=Andrew D. |last2=Sobus |first2=Jon R. |last3=Williams |first3=Antony J. |s2cid=31754962 }}</ref><ref>{{cite journal |last1=Schymanski |first1=Emma L. |author-link=Emma Schymanski |last2=Williams |first2=Antony J. |year=2017 |title=Open Science for Identifying "Known Unknown" Chemicals |journal=Environmental Science and Technology |volume=51 |issue=10 |pages=5357–5359 |bibcode=2017EnST...51.5357S |doi=10.1021/acs.est.7b01908 |pmc=6260822 |pmid=28475325}}</ref>