Automated detection of organophosphate warfare gases (nerve agents) in air based on micro-SIA - lab-on-valve system

Equipment for fast and accurate detection of organophosphate nerve agents is developed and tested. The method is based on the spectrophotometric monitoring of the enzyme activity of butyrylcholinesterase after its contact with air in a special absorption unit (a “scrubber”) developed for the purpose. The scrubber was made from a glass tube filled with glass beads (diam. 3 mm) and filled with approx. 5 ml of butyrylcholinesterase in a phosphate buffer of pH 7.4. The air sample was bubbled through this solution for 20 s at a flow rate of 80 l hour-1. Thereafter 8 microl of the enzyme solution were aspirated into the micro-SIA-LOV analyzer and the activity of the enzymes were evaluated by using Ellman’s reagent, i.e. 2.5 mmol l-1 butyrylthiocholine iodide and 0.25 mmol 5,5’-dithiobis (2-nitrobenzoic acid). The absorbance of the coloured reaction product was measured at 412 nm after the reaction time of 60 s. The residue of the absorption liquid was washed away from the absorber and the system was washed with the enzyme solution prior to next analysis. The contaminated air caused partial inhibition of the enzyme activity of the absorption liquid. The activity of the contaminated sample was compared with the activity of the unaffected enzyme (blank measurement). The analysis was controlled by two PCs. The effect of the concentration of analyte in the absorption liquid on the enzyme activity was tested for 10-5-10-9 mol l-1 sarin. A single analysis (including the absorption step) took <130 s.