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

Monolith/aminated graphene oxide composite-based electric field-assisted solid phase microextraction for efficient capture of phenoxycarboxylic acids herbicides in environmental waters

Efficient capture of strongly polar, ionizable and trace phenoxycarboxylic acids herbicides (PCAHs) from aqueous samples is essential and challenging for environmental monitoring. In the present work, electric field-assisted solid-phase microextraction (EFA-SPME) based on monolith/aminated graphene oxide composite was developed for the first time to efficiently extract trace PCAHs prior to HPLC-tandem mass spectrometry (HPLC-MS/MS) quantification. First, poly (1-allyl-3-methylimidazole difluoromethanesulfonylamide salt-co-divinylbenzene/ethylene dimethacrylate) monolith/aminated graphene oxide composite (MAC) was prepared on the surface of stainless steel wire and employed as the extraction phase of SPME. After that, the MAC-based fiber and a stainless steel wire were connected to a DC power supply that allowed the implement of variable electric fields during adsorption and desorption processes. Various key factors influencing the extraction performance were inspected in detailed. Results well evidenced that the exertion of electric fields improved the enrichment performance, accelerated the trap and release procedures. The proposed MAC/EFA-SPME-HPLC-MS/MS method achieved wide linear ranges (0.005-50.0 μg/L), low limits of detection (0.54-1.3 ng/L) and good precision (2.7-7.0%) for the quantification of PCAHs. The related extraction mechanism was deduced. Additional, the current approach was successfully applied to monitor studied PCAHs at trace contents in environment waters, and the accuracy was confirmed by confirmatory experiments.

Recent advances in the extraction of triazine herbicides from water samples

Pesticides are excessively used in agriculture to improve the quality of crops by eliminating the negative effects of pests. Among the different groups of pesticides, triazine pesticides are a group of compounds that contain a substituted C₃ H₃ N₃ heterocyclic ring, and they are widely used. Triazine pesticides can be dangerous for humans as well as for the aquatic environment because of their high toxicity and endocrine disrupting effect. However, the concentration of these chemical compounds in water samples is low. Moreover, other compounds that may exist in the water samples can interfere with the determination of triazine pesticides. As a result, it is important to develop sample preparation methods that provide preconcentration of the target analyte and sufficient clean-up of the samples. Recently, a wide variety of novel microextraction and miniaturized extraction techniques (e.g., solid-phase microextraction and liquid-phase microextraction, stir bar sorptive extraction, fabric phase sorptive extraction, dispersive solid-phase extraction, and magnetic solid-phase extraction) have been developed. In this review, we aim to discuss the recent advances regarding the extraction of triazine pesticides from environmental water samples. Emphasis will be given to novel sample preparation methods and novel sorbents developed for sorbent-based extraction techniques.

Vortex-assisted solid-phase extraction based on metal-organic framework/chitosan-functionalized hydrophilic sponge column for determination of triazine herbicides in environmental water by liquid chromatography-tandem mass spectrometry

In the presented work, MIL-101(Cr) and chitosan were directly embedded on the skeleton of melamine sponge material using a simple and environmentally friendly method. Chitosan acts not only as an adhesive during the preparation of functionalized sponges, but also as an adsorption adjuvant in herbicide detection. Unlike other polymers, chitosan has excellent hydrophilicity and contains numerous adsorption sites; thus, it enables the sponge material to be used for determination of contaminants in an aqueous phase. Scanning electron microscopic (SEM) analysis showed that the coating material was uniformly distributed on the skeleton of melamine sponge. The prepared material was used as a sorbent in a vortex-assisted solid-phase extraction and combined with high performance liquid phase tandem mass spectrometry for the extraction and trace determination of six triazines in water samples (Atraton, Desmetryn, Prometon, Ametryn, Prometryn and Dimethametryn). Several parameters that affect the extraction efficiencies were investigated. Under the optimal conditions (MIL-101(Cr) loading, 150 mg; sample pH, 7; salt concentration, 0%; adsorption time, 3 min; desorption solvent, 1.5 mL acetonitrile; desorption time, 4 min), the proposed method was successfully used in the determination of trace triazines in five real water samples (drinking water, tap water, lake waters and river water), satisfactory recoveries were obtained in the range of 78.9%-118.6%. The limits of detection of the proposed method in detecting triazine herbicides in spiked water samples ranged from 0.014 to 0.045 ng mL^-1.

Preparation of macroscopic carbon nanohorn-based monoliths in polypropylene tips by medium internal phase emulsion for the determination of parabens in urine samples

A porous monolithic solid based on single-walled carbon nanohorns dahlia-like structure, produced from a medium internal phase emulsion (MIPE), was prepared in a polypropylene tip using UV energy. Thus, single-walled carbon nanohorns (SWNHs) were added to the organic phase where they polymerized in the presence of a radical initiator. A cross-linker (ethylene dimethacrylate, EDMA) was also used in order to obtain a more robust structure. On the other hand, aqueous phase was the responsible for generating the pores in the final solid being inside the droplets generated by the surfactant (Pluronic L121) used to stabilize the polymerization emulsion. Variables related to the formation of the monolithic phase including the stability and composition of emulsion mixture, size of pores, solvent flow resistance and robustness, were studied in detail. In addition, the potential of the SWNH-monolith as extractant phase was evaluated using parabens as target analytes. The LODs ranged from 1 to 7 μg L^-1, while the linear range was extended up to 5000 μg L^-1. The reproducibility of the extraction procedure with different batches of emulsions was acceptable with RSD values < 16% and one prepared SWNH-tip can be used for more than 100 times without apparent extraction losses. The microextraction unit yielded an enrichment factor of 20 for all analytes (extraction efficiency of 100%), with recovery values between 80% and 116% in human urine samples.

Current trends on microextraction by packed sorbent – fundamentals, application fields, innovative improvements and future applications

MEPS, the acronym of microextraction by packed sorbent, is a simple, fast and user- and environmentally-friendly miniaturization of the popular solid-phase extraction technique (SPE).

Porous organic cage incorporated monoliths for solid-phase extraction coupled with liquid chromatography-mass spectrometry for identification of ecdysteroids from Chenopodium quinoa Willd

Here, a porous organic cage (POC)-incorporated polymeric monolith was fabricated in a syringe through the introduction of the POC into poly(ethylene glycol dimethacrylate) monolith in a one-step traditional free-radical polymerization proceess. The resulting monolithic phases were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), nitrogen adsorption/desorption experiments and thermogravimetric analysis (TGA), which confirmed the successful incorporation of the POC in the monolithic matrix. The functionality of the POC-incorporated poly(EDMA) monolith facilitated for the solid phase extraction (SPE) of 20-hydroxecdysone (an ecdysteroid) from Chenopodium quinoa Willd. extract coupled with UPLC-QqQ-MS/MS, exhibiting satisfactory accuracy (93-106%), precision (< 6.5%) and reusability. In addition, UPLC-Q-Exactive-Orbitrap-MS/MS analysis of the quinoa sample after SPE by POC-incorporated monolith provided the identification of 20-hydroxecdysone and three other ecdysteroids. These results demonstrate the potential of POC-incorporated monoliths for the SPE of ecdysteroids from complex plant systems.

Carboxylated single-walled carbon nanotube-functionalized chiral polymer monoliths for affinity capillary electrochromatography

Carboxylated single-walled carbon nanotubes (c-SWNTs) were incorporated into poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) [poly(GMA-co-EDMA)] monoliths to develop a novel monolithic stationary phase for capillary electrochromatography. The prepared monoliths were characterized by scanning electron microscopy and nitrogen adsorption. Additionally, pepsin, which is a chiral selector, was bonded to the c-SWNT-incorporated monoliths via epoxide groups as reactive sites and glutaraldehyde as the spacer. The effects of the c-SWNT concentration on chiral separation were investigated, and the results suggested that the c-SWNTs played a significant role in improving the separation efficiency, although pepsin was the dominant element in determining the chiral recognition ability of the monolith. Moreover, the influences of buffer pH, operating voltage and sample volume were also studied with (±)-nefopam as a model drug. Under the optimized conditions, the pepsin-modified poly(GMA-c-SWNTs-EDMA) monolith exhibited excellent enantioseparation performance for ten pairs of basic chiral drugs and extended the scope of chiral separation of drug enantiomers.

Polymer monolith containing an embedded covalent organic framework for the effective enrichment of benzophenones

A COF modified poly(glycidyl methacrylate–ethylene dimethacrylate) monolith was prepared and used for the microextraction of benzophenones in urine and serum samples.

Preparation and evaluation of micro and meso porous silica monoliths with embedded carbon nanoparticles for the extraction of non-polar compounds from waters

A novel hybrid micro and meso porous silica monolith with embedded carbon nanoparticles (Si-CNPs monolith) was prepared inside a fused silica capillary (3cm in length) and used as a sorbent for solid-phase microextraction. The hybrid monolithic capillary was synthetized by hydrolysis and polycondensation of a mixture of tetraethoxysilane (TEOS), ethanol, and three different carbon nanoparticles such as carboxylated single-walled carbon nanotubes (c-SWCNTs), carboxylated multi-walled carbon nanotubes (c-MWCNTs), and oxidized single-walled carbon nanohorns (o-SWNHs) via a two-step catalytic sol-gel process. Compared with silica monolith without carbon nanoparticles, the developed monolithic capillary column exhibited a higher extraction efficiency towards the analytes which can be ascribed to the presence of the carbon nanoparticles. In this regard, the best performance was achieved for silica monolith with embedded c-MWCNTs. The resulted monolithic capillaries were also characterized by scanning electron microscopy (SEM), elemental analysis and nitrogen intrusion porosimetry. Variables affecting to the preparation of the sorbent phase including three different carbon nanoparticles and extraction parameters were studied in depth using polycyclic aromatic hydrocarbons (PAHs) as target analytes. Gas chromatography-mass spectrometry was selected as instrumental technique. Detection limits range from 0.1 to 0.3μgL^-1, and the inter-extraction units precision (expressed as relative standard deviation) is between 5.9 and 14.4%.