Study On The New Methods For Clectrochemical Determination Of Isocarbophos In Vegetables

Isocarbophos (ICP), one of the chiral organophosphorus pesticides (OPs), hasplayed an important role in increasing agricultural productivity because of itseffectivity for killing destructive insects and easy to break down under alkalineconditions. But overuse and abuse have resulted in residue problems in theenvironment and cause risks to human health through the enrichment of the foodchain, which may impact on the metabolic balance of the hormones of the humanbody, especially on the normal development of children’s nervous system. As weknow, the poison incident of Hainan cowpea in2010was basically caused by ICP.Therefore, it is an important issue to develop new methods for detecting isocarbophos,in particular at trace level. This paper presented two novel molecularly imprintedpolymer (MIP) modified sensors for electrochemical determination of ICP. Themorphologic features of the molecularly imprinted membrane-modified glassy carbonelectrode (GCE) were observed by electrochemical technology. The experimentalparameters that affect the performance of the imprinted sensors were investigated andoptimized. The selectivity, reproducibility, and stability of the ICP sensors have alsobeen tested. The applicability of the proposed methods was examined by determiningthe ICP concentration in cabbage and cowpea samples using standard addition method.The results suggest a promising feature in application of the proposed MIP sensors tothe detection of ICP in real samples. Considering that ICP is electro-inactive over thestudied potential range, an electroactive substance, hexacyanoferrate, was chosen asthe redox probe of the two MIP modified sensors in the determination process.(1) Based on molecularly imprinted technology, a isocarbophos sensor wasprepared by electropolymerization of MIP film at the surface of GCE witho-phenylenediamine (o-PD) and gallic acid (GA) as functional monomers, ICP as the template. The MIP membrane (pGA-PD) was characterized by cyclic voltammetry(CV), differential pulse voltammetry (DPV) and electrochemical impedancespectroscopy (EIS). Several important parameters controling pGA-PD film propertieswere studied and optimized through DPV. Under the optimal experimental condition,the relative change of reduction peak current of the potassium ferricyanide was linearto ICP concentration and the linear range was2.00×10~-7~2.00×10-4mol/L with anequation of Δi(μA)=13.2293-0.0483C (μmol/L, r2=0.9982). The detection limit iscalculated to be6.06×10-8mol/L (S/N=3). The MIP sensor was successfully appliedto detect isocarbophos in vegetables with high selectivity, sensitivity andreproducibility.(2) A novel electrochemical sensor with sensitive and selective binding sites forisocarbophos detection was prepared, which is based on a GCE modified withmolecularly imprinted terpolymer of poly(o-phenylenediamine-co-gallicacid-co-m-aminobenzoic acid)(p(PD-GA-ABA)) templated with ICP. The surfacefeature of the p(PD-GA-ABA) modified GCE was characterized by CV, DPV and EIS.Several important parameters controlling the performance of the sensor wereinvestigated and optimized. Under optimal conditions, the changes in DPV peakcurrents of hexacyanoferrate were linear to ICP concentrations in the range from7.50×10-8to5.00×10-5mol/L and5.00×10~-5to1.00×10~-4mol/L, with the detectionlimit of2.01×10~-8mol/L (S/N=3). The method was applied successfully to determineICP in vegetables with satisfactory precision (2.30~5.28%of RSD) and acceptablerecoveries (95.5~110.0%).