TOP Assay
{{Short description|Laboratory analysis method}}
The TOP Assay (Total Oxidizable Precursor Assay) is a laboratory method developed in 2012{{Cite journal |last1=Houtz |first1=Erika F. |last2=Sedlak |first2=David L. |date=2012-09-04 |title=Oxidative Conversion as a Means of Detecting Precursors to Perfluoroalkyl Acids in Urban Runoff |url=https://pubs.acs.org/doi/10.1021/es302274g |journal=Environmental Science & Technology |language=en |volume=46 |issue=17 |pages=9342–9349 |bibcode=2012EnST...46.9342H |doi=10.1021/es302274g |issn=0013-936X |pmid=22900587|url-access=subscription }} that oxidatively converts (unknown) precursor compounds of perfluorocarboxylic acids (PFCAs) into the latter. This makes quantification possible. Potassium peroxodisulfate is used. This sum parameter can be used to determine the concentration of precursor compounds present by comparing the sample before and after the application of the TOP Assay.{{Cite journal |last1=Göckener |first1=Bernd |last2=Fliedner |first2=Annette |last3=Rüdel |first3=Heinz |last4=Fettig |first4=Ina |last5=Koschorreck |first5=Jan |date=August 2021 |title=Exploring unknown per- and polyfluoroalkyl substances in the German environment – The total oxidizable precursor assay as helpful tool in research and regulation |journal=Science of the Total Environment |volume=782 |pages=146825 |doi=10.1016/j.scitotenv.2021.146825 |pmid=33838381 |bibcode=2021ScTEn.78246825G |issn=0048-9697|doi-access=free }}
Application
This method is used, for example, in the analysis of fire-fighting foams (aqueous film forming foam), textiles or water samples.{{Cite journal |last1=Al Amin |first1=Md |last2=Luo |first2=Yunlong |last3=Nolan |first3=Annette |last4=Robinson |first4=Fiona |last5=Niu |first5=Junfeng |last6=Warner |first6=Scott |last7=Liu |first7=Yanju |last8=Dharmarajan |first8=Raja |last9=Mallavarapu |first9=Megharaj |last10=Naidu |first10=Ravi |last11=Fang |first11=Cheng |date=December 2021 |title=Total oxidisable precursor assay towards selective detection of PFAS in AFFF |url=https://doi.org/10.1016/j.jclepro.2021.129568 |journal=Journal of Cleaner Production |volume=328 |pages=129568 |doi=10.1016/j.jclepro.2021.129568 |bibcode=2021JCPro.32829568A |issn=0959-6526|url-access=subscription }}{{Cite journal |last1=Ignacio |first1=Ma Cristine Concepcion D. |last2=Curtzwiler |first2=Greg W. |last3=Early |first3=Mark R. |last4=Updegraff |first4=Katie M. |last5=Vorst |first5=Keith L. |date=February 2023 |title=Ion Selective Electrode (ISE) Method for Determination of Total Fluorine and Total Organic Fluorine in Packaging Substrates |journal=Methods and Protocols |language=en |volume=6 |issue=1 |pages=10 |doi=10.3390/mps6010010 |doi-access=free |issn=2409-9279 |pmc=9959142 |pmid=36827497}} Blood serum can also be analyzed in this way.{{Cite journal |last1=Cioni |first1=Lara |last2=Nikiforov |first2=Vladimir |last3=Coêlho |first3=Ana Carolina M.F. |last4=Sandanger |first4=Torkjel M. |last5=Herzke |first5=Dorte |date=December 2022 |title=Total oxidizable precursors assay for PFAS in human serum |url=https://doi.org/10.1016/j.envint.2022.107656 |journal=Environment International |volume=170 |pages=107656 |doi=10.1016/j.envint.2022.107656 |pmid=36436462 |bibcode=2022EnInt.17007656C |issn=0160-4120|hdl=10037/27580 |hdl-access=free }}
Neutral, anionic and cationic precursor compounds may be distinguished using an extension of the method published in 2025.{{Cite journal |last=Antell |first=Edmund H. |last2=Yi |first2=Shan |last3=Olivares |first3=Christopher I. |last4=Chaudhuri |first4=Shreya |last5=Ruyle |first5=Bridger J. |last6=Alvarez-Cohen |first6=Lisa |last7=Sedlak |first7=David L. |date=2025-02-13 |title=Selective Quantification of Charged and Neutral Polyfluoroalkyl Substances Using the Total Oxidizable Precursor (TOP) Assay |journal=Environmental Science & Technology |doi=10.1021/acs.est.4c13837|doi-access=free |pmc=11866920 }}
In addition to fluorotelomer compounds, hydrogen-substituted perfluorosulfonic acids (Hn-PFSAs), for example, can also be oxidized using the TOP Assay. Saturated and unsaturated perfluorosulfonic acids as well as perfluoroalkyl ether sulfonic acids, on the other hand, are stable.{{Cite journal |last1=Zweigle |first1=Jonathan |last2=Bugsel |first2=Boris |last3=Röhler |first3=Klaus |last4=Haluska |first4=Alexander Arthur |last5=Zwiener |first5=Christian |date=2023-04-25 |title=PFAS-Contaminated Soil Site in Germany: Nontarget Screening before and after Direct TOP Assay by Kendrick Mass Defect and FindPFΔS |url=https://pubs.acs.org/doi/10.1021/acs.est.2c07969 |journal=Environmental Science & Technology |language=en |volume=57 |issue=16 |pages=6647–6655 |doi=10.1021/acs.est.2c07969 |pmid=37058300 |bibcode=2023EnST...57.6647Z |issn=0013-936X|url-access=subscription }}
Further reading
- {{Cite journal |last1=Ateia |first1=Mohamed |last2=Chiang |first2=Dora |last3=Cashman |first3=Michaela |last4=Acheson |first4=Carolyn |date=2023-04-11 |title=Total Oxidizable Precursor (TOP) Assay─Best Practices, Capabilities and Limitations for PFAS Site Investigation and Remediation |journal=Environmental Science & Technology Letters |language=en |volume=10 |issue=4 |pages=292–301 |doi=10.1021/acs.estlett.3c00061 |issn=2328-8930 |pmc=10259459 |pmid=37313434|bibcode=2023EnSTL..10..292A }}