Multiwall carbon nanotube-g-(agarose-g-polymethyl methacrylate) and (agarose-g-polymethyl methacrylate) sorbents for extraction of pesticides and heavy metal ions from aqueous matrices

Abstract

Rapid developments in agriculture and industrial sectors have increased the levels of toxic heavy metals and pesticide residues in the environment. Many sample pretreatment methods utilized in the determination of heavy metals and pesticide residues are often time consuming, labor intensive and require substantial amounts of organic solvents. Thus, new approaches in miniaturized sample preparation are imperative. In this study, new modified agarose sorbents were prepared, characterized and applied to the extraction and pre-concentration of pesticides and heavy metal ions from aqueous matrices. Poly(methyl methacrylate)-grafted-agarose (Agarose-g-PMMA) was successfully synthesized using microwave radiation and ceric ammonium nitrate (CAN) as the radical initiator. The optimum condition for graft copolymerization was found to be at 9 g monomer, 0.4 g CAN, 60 s microwave irradiation time under 700W microwave radiation for 1 g of agarose. The graft copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy, CHN analysis, field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC) analysis, thermal gravimetric analysis (TGA) and gel permeation chromatography (GPC). A micro-solid phase extraction (µ-SPE) utilizing Agarose-g-PMMA as sorbent combined with gas chromatography-microelectron capture detection was developed for the determination of selected pesticides, namely diazenon, chlorpyrifos, hexaconazole and azaconazole in water samples. Under optimized conditions, low limits of detection (LODs) (0.004 - 0.024 ng mL-1) were obtained with good recoveries (82.23 - 103.58%). Agarose-g-PMMA was also employed as sorbent in dispersive micro-solid phase extraction (D-µ-SPE) combined with inductively coupled plasma-mass spectrometry for the analysis of heavy metals namely cadmium, nickel, copper and zinc in vegetables and natural water samples. Under the optimum conditions, the developed method showed excellent LODs (0.6 - 1.8 ng L-1) and good relative recoveries (92.0 - 103.0%) for the analytes. The Agarose-g-PMMA was covalently-modified with multi-walled carbon nanotubes (MWCNTs) and the composite formed (MWCNTs-g-Agarose-g-PMMA) was characterized by FTIR, TGA and transmission electron microscopy (TEM). A SPE method incorporating MWCNTs-g-Agarose-g-PMMA as sorbent was developed and combined with flame atomic absorption spectrometry for the determination of lead ions in natural water samples. The method provided fast analysis and showed good sensitivity and excellent precision and suitable for extraction and pre-concentration of pesticide residues and trace metal ions in water and vegetable samples.