Improved microextraction of selected triazines using polymer monoliths modified with carboxylated multi-walled carbon nanotubes

This article reports on the enhancement of the capacity of an acrylate-based monolithic solid sorbent by anchoring carboxylated multi-walled carbon nanotubes (c-MWCNTs) in its pores and on its surface. Monolithic poly(butyl acrylate-co-ethyleneglycol dimethacrylate) [poly(BA-co-EGDMA)] was synthetized inside a fused silica capillary via free-radical polymerization, and an ethanolic dispersion of c-MWCNTs was passed through the capillary. The resulting poly(BA-co-EGDMA-c-MWCNTs) monolith was characterized by scanning electron microscopy to confirm the presence of the c-MWCNTs. The effect of using three different kinds of carbon nanoparticles and the microextraction step were studied using triazine herbicides as model compunds. The use of c-MWCNTs resulted in best performance in terms of extraction enhancement (compared to carboxylated single-walled carbon nanotubes and oxidized single-walled carbon nanohorns). The use of these carbon nanoparticles improved the extraction of triazines in any case when compared to using a bare poly(BA-co-EGDMA) monolith. The triazines were then quantified by gas chromatography with mass spectrometric detection. Detection limits ranged from 0.03 to 0.1 mu g center dot L-1 (except for simazine; 0.6 mu g center dot L-1), and the precision (relative standard deviation) varied between 3.0 and 11.4 %. The reproducibility between units is < 14.3 % (expressed as relative standard deviation) which demonstrates the robustness of the method. The method was applied to analyze an unknown sample of orange juice and gave a value of 0.18 mu g center dot L-1 for prometryn. Finally, the analysis of spiked samples of water and orange juices yielded recoveries ranging from 81 to 113 % and 75 to 125 %, respectively.