Effect of oxidation and dimensions of multi-walled carbon nanotubes on solid phase extraction and enrichment of some pesticides from environmental waters prior to their simultaneous determination by high performance liquid chromatography

In this novel study, some factors that affect the enrichment efficiency of multi-walled carbon nanotubes (MWCNTs) towards some pesticides in environmental water samples were studied. The effect of oxidation of MWCNTs with various oxidizing agents and the effect of length and external diameter of MWCNTs were investigated. Model pesticides were selected from various common categories of pesticides, viz. Atrazine, Propoxur, Methidathion. Variables optimized included external diameter and length of the MWCNT, oxidation of the MWCNT, mass of the MWCNT, volume and pH of water sample, composition and volume of eluting solvent and washing solvent. It was found that short-nitric acid oxidized-MWCNT exhibited higher enrichment efficiency, especially for Methidathion, than non-oxidized long MWCNT. The optimized SPE procedure is capable of determining Propoxur (detection limit: 220 ng L−1, linear range: 10–50 ng mL−1, <3.0% RSD), Atrazine (detection limit: 57.5 ng L−1, linear range: 10–100 ng mL−1, <2.8% RSD) and Methidathion (detection limit: 37.5 ng L−1, linear range: 10–50 ng mL−1, <2.5% RSD). Application of the optimized SPE procedure to determine the three target pesticides in real environmental waters (tap water, reservoir water and stream water) gave spike recoveries in the range of 81.0–108%.