Bis(2,4,6-trichlorophenyl)oxalate-based chemically initiated electron exchange chromogenic reaction system for colorimetric detection of fentanyl and norfentanyl

A series of colorimetric chromogenic substrates such as 3, 3′, 5, 5′-tetramethylbenzidine (TMB), o-phenylenediamine (OPD), diazoaminobenzene (DAB), and 2,2ʹ-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) have been employed for developing chromogenic reactions. In the present work, we develop a series of chemically initiated electron exchange chromogenic (CIEEC) reaction systems, in which TCPO is oxidized by H2O2 to produce biradical intermediate that further oxidizes chromogenic substrates such as TMB, OPD, DAB, or ABTS in an ethanol-water mixture, inducing an optical absorption and color change. We present a visual colorimetric assay based on the TCPO-H2O2-TMB CIEEC reaction for detection of hydrophobic fentanyl (FTN) and norfentanyl (NFTN) that are new psychoactive substances and illicit drugs.