Sol-gel organic-inorganic hybrid polydimethysiloxane-3- aminopropyltrimethoxysilane as sorbent for stir bar sorpitive extraction of organophosphorus pesticides

Abstract

An organic-inorganic hybrid 3-aminopropyltrimethoxysilane (APTMS)- polydimethylsiloxane (PDMS) was produced using sol-gel method and used as coating on glass encased stir bar. The physico-chemical properties and extraction ability of the APTMS/PDMS hybrid coatings were manipulated by varying the molar ratio of APTMS to PDMS, amount of water and types of catalysts during sol synthesis. Fourier Transform Infrared Spectroscopy results showed successful hybridization between PDMS and amino moiety. Field Emission Scanning Electron Microscopy showed a homogenous surface image of the APTMS/PDMS hybrid coating while nitrogen adsorption indicated that the hybrid is a mesoporous material (pore size ~2.9 nm). The ability of the APTMS/PDMS hybrid coatings were investigated for stir bar sorptive extraction (SBSE) of two selected organophosphorus pesticides (OPPs) namely polar dicrotophos and mid-polar malathion. Analysis was performed using HPLC with UV detector. Optimized SBSE parameters using APTMS/PDMS hybrid coating were 300 rpm stirring rate, 15 min extraction time, 1 mL methanol as ultrasonic assisted liquid desorption (UA-LD) solvent and 25 min desorption time. The optimized SBSE parameters using PDMS-coated TWISTER were also similar with the APTMS/PDMS hybrid coating except that the stirring rate used was 600 rpm. The limit of detection (LOD) (S/N=3) of dicrotophos is 0.108 mg L-1 and 0.158 mg L-1 for malathion using APTMS/PDMS hybrid coating. LOD (S/N=3) of malathion is 0.31 mg L-1 but dicrotophos was not detected with the PDMS-coated TWISTER. The APTMS/PDMS sol-gel coating developed for SBSE was successfully applied for the determination of OPPs in grape and cucumber samples, and its performance was compared with commercial PDMS TWISTER. The recoveries of dicrotophos and malathion from cucumber and grape samples using APTMS/PDMS hybrid coating was 71% and 98%, respectively with RSD 3.1%-3.6%. The recoveries of malathion in cucumber and grape using PDMS-coated TWISTER was 91% and 62% respectively, with acceptable RSD 7.46%. SBSE using APTMS/PDMS hybrid coating showed better selectivity for the polar dicrotophos compared to commercial PDMS-coated TWISTER, which failed to extract the polar dicrotophos.