Enzymatic Determination of Anticholinesterases Using a Composite Carrier

A modified enzyme method is reported for the determination of cholinesterase inhibitors based on the use of a granulated composite carrier with immobilized butyrylcholinesterase. The detection system includes butyrylthiocholine as the substrate and N-(2,3-dimethyl-5-oxo-1-phenyl-3-pyrazoline-4-yl)-2-chloro-5-sulpho-4-iminobenzoquinone as a redox indicator. This method was characterized using carbamate physostigmine and sarin (O-isopropyl methylphosphonofluoridate). The method was also used in a simple tube detector. Evaluation was based on the observation with the naked eye of the decolorization of the redox indicator in comparison to a control time and by tristimulus colorimetry. The limits of detection were 0.5 µg/mL for physostigmine and 7 × 10−4 mg/m3 for sarin visually, or 0.06 µg/mL for physostigmine and 1.1 × 10−4 mg/m3 for sarin by colorimetry.