Electrochemical impedance spectroscopy study of the response of phthalic acid esters on the azolla modified copper electrode

Phthalic acid esters (PAEs) are a group of hand-made chemicals used as softener, stabilizer or additive in many consumers and industrial products. Humans are exposed to these substances throughout their lives, even in the womb through maternal contact [۱]. They lower۲testosterone and cause abnormalities in the male reproductive system and may cause carcinogenic effects and genetic damage. These substances may enter the environment during production, use or destruction of products and cause pollution to water, soil and atmosphere [۲]. In this work, a sensitive and efficient electrochemical sensor was introduced and the interacton of four phthalic acid esters (PAEs) including dibutyl phthalate (DBP), dimethyl phthalate (DMP), di(۲-ethylhexyl) phthalate (DEHP) and dicyclohexyl phthalate (DCHP) in aqueous solutions with this biosensor was separately investigated by electrochemical impedance spectroscopy (EIS). The surface of a copper electrode was modified by azolla paste prepared using azolla powder and the electroencephalography gel (EEG). For this purpose, sufficient amount of azolla fern was collected from Anzali wetland, washed by deionized water, dryied and grounded to produce powders with the particle size of < ۷۴ microns. The azolla powder was characterized by FESEM, TEM, BET, FT-IR and EDX methods. Determination of PAEs was conducted based on their blocking effect on the electrode surface for ferrous ions oxidation. Due to the Nyquist plots, the charge transfer resistance (RCT) of bare electrode and azolla modified electrode were ۴۶۸.۸ and ۴۳۸.۷ kΩ, respectively. After separately injection of ۳ μg L-۱ DBP, DMP, DEHP and DCHP, RCT were obtained as ۵۶۳.۹, ۵۸۸.۵, ۵۴۸.۷ and ۵۷۰.۱ kΩ, respectively. By taking a closer look, spatial hindrance of PAEs play major role in RCT shifts. The blockers with smaller structure provide the better point-by-point coverage of surface which conclude the bigger shift in the RCT. So, the blocking properties of PAEs was confirmed. The above-mentioned results, give us exciting sign of future opportunity for developing the impedimetric biosensor of PAEs. This biosensor will work based on the RCT shifts versus PAEs concentration. It is clear that the small changes in carbonyl group polarity in the PAEs structure will affect ΔRCT and bring selectivity for impedimetric biosensor of PAEs. According to the results this biosensor can be used to determine PAEs in real aqueous samples.

کلیدواژه ها:

Azolla modified electrode ، Biosensor ، Phthalic acid esters ، Electrochemical impedance spectroscopy