Solid-phase extraction cartridges with multi-walled carbon nanotubes and effect of the oxygen functionalities on the recovery efficiency of organic micropollutants

Abstract

Pristine and functionalized multi-walled carbon nanotubes (MWCNTs) were investigated as adsorbent materials inside solid-phase extraction (SPE) cartridges for extraction and preconcentration of 8 EU-relevant organic micropollutants (with different pKa and polarity) before chromatographic analysis of surface water. The recoveries obtained were > 60% for 5/8 target pollutants (acetamiprid, atrazine, carbamazepine, diclofenac, and isoproturon) using a low amount of this reusable adsorbent (50 mg) and an eco-friendly solvent (ethanol) for both conditioning and elution steps. The introduction of oxygenated surface groups in the carbon nanotubes by using a controlled HNO3 hydrothermal oxidation method, considerably improved the recoveries obtained for PFOS (perfluorooctanesulfonic acid) and methiocarb, which was ascribed to the hydrogen bond adsorption mechanism, but decreased those observed for the pesticide acetamiprid and for two pharmaceuticals (carbamazepine and diclofenac), suggesting π–π dispersive interactions. Moreover, a good correlation was found between the recovery obtained for methiocarb and the amount of oxygenated surface groups on functionalized MWCNTs, which was mainly attributed to the increase of phenols and carbonyl and quinone groups. Thus, the HNO3 hydrothermal oxidation method can be used to finely tune the surface chemistry (and texture) of MWCNTs according to the specific micropollutants to be extracted and quantified in real water samples.

Carbon xerogels combined with nanotubes as solid-phase extraction sorbent to determine metaflumizone and seven other surface and drinking water micropollutants

“…In the present work, pristine and hydrothermally modified CXs were synthetized, characterized and applied as SPE adsorbents for the simultaneous extraction of 8 EU multi-class OMPs in water samples, namely 5 pesticides (acetamiprid, atrazine, isoproturon, metaflumizone, and methiocarb), 2 pharmaceuticals (carbamazepine and diclofenac) and 1 industrial compound (perfluorooctanesulfonic acid), followed by analysis with UHPLC-MS/MS. SPE cartridges packed with multi-walled carbon nanotubes (MWCNTs) performed well for 7 out of these 8 target compounds in our previous study 36 , but failed to recover metaflumizone, which is included in the very recent Watch List of EU Decision 2020/1161 5 . Therefore, upon broadening the range of carbon materials explored, the goal of the present study was to find a sorbent with a good performance for the recovery of metaflumizone, aiming at the development of a SPE carbon-based cartridge in multi-layer configuration performing well for all the 8 OMPs.…”

“…Hydrochloric acid, ethanol (HPLC grade), and methanol (MS grade) were purchased from VWR International (Fontenay-sous-Bois, France). The stock solution and the working solutions were prepared according our previous work 1 , 36 . Briefly, the stock solution was prepared in ethanol with 1000 mg L −1 of each reference or internal standard and the working solutions comprising all the target compounds or the internal standards (2.5 mg L −1 and 5.0 mg L −1 , respectively) were prepared by dilution of the individual stocks in ethanol.…”

“…Two types of carbon materials were used in this work, namely in-house prepared CXs and commercial MWCNTs. More details (i.e., textural and surface chemistry characterization) on the MWCNTs can be found in our previous publication 36 . The pristine CX material was prepared by polycondensation of resorcinol with formaldehyde using a molar ratio of 1:2, adapting the procedures described elsewhere 20 , 22 .…”

“…Handmade cartridges with single (i.e., containing a CX sample only) and multi-layer configuration (i.e., with both CX and MWCNT) were packed by using a device specially created for that purpose 36 . This process comprises several successive phases, namely: (i) a polyethylene frit (20 µm) was positioned on the bottom of an empty SPE cartridge (6 mL); (ii) a selected amount of carbon material was then introduced in the cartridge; (iii) the carbon sample was protected with another frit; and (iv) a slight compression was applied until a specific bed height was achieved.…”

“…The SPE procedure applied is described in our previous works 1 , 36 . Briefly, the conditioning solvents ethanol or methanol and ultrapure water were successively passed through the SPE cartridge at a flow rate of 1 mL min −1 .…”