Chemically modified halloysite nanotubes as a solid-phase microextraction coating.

Halloysite nanotubes were modified in three simple steps including etching, hydroxylation and amino grafting. The sol-gel technique was used for the chemical bonding of the modified halloysite nanotubes (MHNTs) to fused-silica support. The MHNTs, as a novel adsorbent was applied as a SPME coating. Diazinon, parathion and fenthion were selected as the model compounds to study the extraction efficiency of the coating. Gas chromatography-corona discharge ion mobility spectrometry was applied for the analysis of the extracted analytes. The parameters influencing the extraction efficiency of the method, such as stirring rate, salt effect, extraction temperature and time were optimized. The results showed that the MHNTs fiber had better extraction efficiency than the commercial SPME (PA, PDMS, and PDMS-DVB), bare silica, silica-based HNTs and HNTs-titanium dioxide fibers. The limits of detection were found to be in the range of 0.01-0.03 μg L-1 . The limits of quantification were in the range of 0.03-0.07 μg L-1 . Also, a good linearity in the range of 0.03-3.0, 0.07-2.0 and 0.03-3.0 μg L-1 , was found for diazinon, fenthion and parathion, respectively. The method precision was lower than 7.0 and 8.7% as the intra- and inter-day relative standard deviations, respectively. Agricultural wastewater, cucumber and apple were chosen as the real samples. The spiking recovery values were between 84 (±9) and 97% (±6). The results showed that the method was applicable and suitable for real samples analysis.