FLOW-INJECTION DETERMINATION OF PARAOXON BY INHIBITION OF IMMOBILIZED ACETYLCHOLINESTERASE

Two flow-injection methods (continuous-flow and stopped-flow) are proposed for the determination of paraoxon, applying the dual-injection technique and spectrophotometric detection. They are based on the inhibition of the acetylcholinesterase-catalysed hydrolysis of α-naphthyl acetate and subsequent reaction of the α-naphthol produced with p-nitrobenzenediazonium fluoroborate. For the continuous-flow system the calibration graph was linear from 5 × 10-7 to 1.5 × 10-5 M, the relative standard deviation (r.s.d.) (n=6) for an 8 × 10-6 M standard was 1.4%, the limit of detection (3σ) was 4 × 10-7 M and the sample throughput was ca. 60 h-1. For the stopped-flow system the linear range was from 1 × 10-8 to 4 × 10-7 M, the r.s.d. for a 2.5 × 10-7 M standard was 0.9%, the limit of detection was 8 × 10-9 M and the sample throughput was 30 h-1. © 1990.