We firstly studied the UV-vis absorbance spectroscopic
characteristics of the above reaction in the absence and presence
of methyl parathion, respectively, over an extended period
of reaction time. Fig. 1a shows the obtained spectra of the
reaction in the absence of methyl parathion. From the spectra,
two peaks are observed; the absorbance at 320 nm that corresponds
to the maximum absorption by DTNB decreases with
increasing time, while the peak at 412 nm increases. The
absorbance band at 412 nm corresponds to TNB and reflects
its production during the reaction; increased concentrations
of TNB result in an increased, higher yellow intensity of the
solution. After 50 min, this peak becomes stable, indicating
the completion of the reaction.