Electrochemical oxidation of diazinon in aqueous solutions via electrogenerated halogens – Diazinon fate and implications for its detection

Organophosphorous pesticide diazinon was indirectly oxidized to diazoxon by means of electrogenerated Cl2, Br2 or I2 under galvanostatic conditions using rotating glassy carbon disk electrode. The rate of oxidation was the highest in the case of electrogenerated Br2. In the presence of electrogenerated Br2 diazinon was completely converted to diazoxon after 15 min of electrochemical treatment at all concentrations investigated. On the basis of thermodynamic and kinetic arguments it was showed that diazinon oxidation is governed by both kinetics and speciation of halogen species. Diazoxon is rapidly formed during its reaction with active oxidant species, while formed diazoxon is being stable and not degraded at appreciable rate by reactive halogen species. Described oxidation procedure was used as a pre-step for diazinon detection using AChE test coupled with optical detection. Diazinon detection limit was reduced by three orders of magnitude compared to unoxidized diazinon. This enabled diazinon detection at the lowest possible concentration using described methodology, as determined by diazoxon detection limit.