Abstract: A method comprising an unknown solution adding an organophosphorus thio a salt solution for sufficient time to form compounds having anticholinesterase activity in the reaction solution, contacting the reaction solution with a cholinesterase supported on a suitable substrate, adding indoxyl acetate and observing a non-color or blue color change in the substrate; the absence of color indicates the formation of compounds with anticholinesterase activity and the blue color of the substrate indicating that there was no formation of compounds with anticholinesterase activity.