Application Of Single-walled Carbon Nanotubes As Sorbent In The Determination Of Pesticides In Aqueous Samples

Solid phase extraction (SPE) and solid phase microextraction (SPME) are the most widely used sample preparation techniques. As a type of new carbonaceous material, carbon nanotubes (CNTs) have been used as sorbent or coating in SPE and SPME, respectively. However, the cartridge filled with CNTs needs large amount of CNTs, and is with low utilization efficiency of absorbing sits and high flow resistance. The preparation of core-shell CNTs nanocomposite supported by inorganic material is partly a solution to these problems. However, the preparation methods are complex, use numerous chemicals, require strictly controlled reaction conditions, and small amount of CNTs are attached to the supporting material. These shortcomings limit greatly the application of CNTs in SPE. In addition, the SPME fiber made from Pt fiber, covered by SWCNTs and prepared by electrophoretic deposition is of excellent performance, but it’s applications in the analysis of pesticides in water are rare. Targeting to above problems, this study developed a simple and straightforward method to prepare a nanocomposite with core-shell structure by covering silica gel with SWCNTs (SWCNTs@Silica). SWCNTs@Silica was use as SPE sorbent in the analysis of acetanilide herbicides (AAHs) and organophosphorus pesticides (OPPs) in water samples. The SWCNTs SPME fiber was prepared and applied in the analysis of fungicides and acaricide in water sample. The obtained results are as follows.(1) Preparation and characterization of SWCNTs@Silica. The SWCNTs solution was added step by step to the the powder of silica gel. When the SWCNTs was concentrated by evaporating the solvent, SWCNTs aggregated and formed film on the silica surface because of the presence of Van Der Wallas force between SWCNTs. Therefore, SWCNTs@Silica was prepared. The observation with an optical microscope showed that the silica particles were fully covered by SWCNTs, the morphology and size of the prepared SWCNTs@Silica were similar to those of original silica gel. Compared to the method using chemical reaction to bond SWCNTs to the surface of supporting material, this method is simple, easy to follow, with less steps, and no chemical reaction is needed.(2) Evaluation of the SPE cartridge filled with SWCNTs@silica for the extraction of AAHs and the establishment of the related analytical method. The results showed that the use of SWCNTs@Silica as SPE sorbent would reduce dramatically the amount of CNTs used, and thus increase the utilization rate of absorbing site on SWCNTs; SWCNTs@Silica can stand with a pH as low as1; the loading flow rate was the same as that of the silica cartridge; the conditioning step, which is needed for the common SPE cartridge, could be omitted. The LODs and LOQs of the established method were0.475-0.710ng/L, and1.56-2.34ng/L, respectively. Acetochlor and butachlor were determined when this method was applied to analyze river water from Jiulong river. It means that the method meet the requirement of practical environmental monitoring.(3) Evaluation of the SPE cartridge filled with SWCNTs@silica for the extraction of OPPs and the establishment of the related analytical method. The results shows that the use of SWCNTs@Silica as SPE sorbent could omit the conditioning step, which is needed for the common SPE cartridge; The extraction efficiency of SWCNTs@Silica cartridge was lower than that of HLB cartridge, but was higher than that of C18cartrdge; the breakthrough volume of the polar OPPs, mevinphos and dimethoate, was up to100mL, showing affinity of SWCNTs@Silica for polar compounds. The LODs and LOQs of the established method were0.593-1.759μg/L and1.95-5.80μg/L, respectively. Chlorpyrifos and triazophos were detected when this method was applied to analyze river water from Jiulong river and farm field water from Xiangan. It means that the method meet the requirement of practical environmental monitoring.(4) A new analytical method was established based on SWCNTs SPME fiber for the analysis of fungicides and acaricide in water sample. The results shows that the annealing process of SWCNTs fiber could improve significantly the extraction efficiency; with excellent chemical stability, the prepared fiber perform very well with a pH as low as1. The analytical time of the established method for one sample was45 min. The LODs and LOQs of the established method were0.022-0.987μg/L,0.075-3.259μg/L, respectively.