Hexagonal boron nitride nanosheets as adsorbents for solid-phase extraction of polychlorinated biphenyls from water samples

Tetrazine-based dynamic covalent polymers as degradable extraction materials in sample preparation

BACKGROUND

Current trends in Analytical Chemistry are highly focused on the introduction of new extraction materials with a high selectivity towards the target analytes, high extraction capacity as well as sustainable characteristics. In this context, the introduction of smart materials able to respond to an external stimulus constitutes a promising approach in the field. However, investigations regarding the development of such stimuli-responsive polymers have been basically centered on their synthesis and the control of their properties, and hardly on exploiting such properties to generate polymers that, once their extraction function is fulfilled, they can be degraded into fragments with little or negligible toxicity, or even into their constituent monomers for an efficient recycling.

RESULTS

The applicability of a degradable and recyclable dynamic covalent polymer based on the use of tetrazine as a linker was assessed as sorbent for the extraction of a group of 37 persistent organic pollutants, including 10 polycyclic aromatic hydrocarbons, 11 organochlorine pesticides, 14 polychlorinated biphenyls, and 2 antibacterial agents, from water samples. A microdispersive solid-phase extraction procedure was developed for the selective extraction of the target analytes, while their separation, determination, and quantification were achieved by gas chromatography coupled to mass spectrometry. The optimized procedure was validated for seawater and wastewater obtaining mean relative recovery values between 72 and 112 % for almost all the analytes, with satisfactory relative standard deviation values (<18 %). After extraction, the polymer could be degraded by adding the amino acid L-tyrosine, being possible a quantitative recovery of the initial functional monomer.

SIGNIFICANCE

A responsive polymer based on the chemical versatility of the tetrazine ring was used as sorbent in sample preparation providing excellent results, showing good physicochemical properties and the ability to be degraded after use. This polymer constitutes an interesting alternative to reduce chemical waste through the recycling of monomers, contributing to the development of more sustainable analytical methodologies.

Ant nest-like hierarchical porous imprinted resin-dispersive solid-phase extraction for selective extraction and determination of polychlorinated biphenyls in milk

Polychlorinated biphenyls (PCBs) are persistent toxic, organic chemicals that tend to accumulate in the food chain. This study reports the rapid and selective extraction and determination of PCBs (PCB81, 153, 105, 126, and 157) in milk samples by a dispersive solid-phase extraction (DSPE) coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS). An ionic liquid-molecularly imprinted porous resin (IL-MIPPR) as a DSPE adsorbent was synthesized from m-aminophenol, formaldehyde, and 2,2'-benzidinedisulfonic acid as the monomer, crosslinker, and virtual template, respectively. The IL-MIPPR had a fast mass transfer (1.0 min) and good selectivity (imprinting factors of 1.8-3.0). The IL-MIPPR - DSPE - GC-MS/MS method exhibited good linearity (R² ≥ 0.9995), the limit of detections (LODs) < 0.6 pg/g, and the recoveries ranged from 82.8 % to 106 % with relative standard deviations ≤ 6.6 %. This method is thus better than previously reported methods in terms of the LOD, the adsorbent dosage, and the extraction time.

Au@BN-enhanced laser desorption/ionization mass spectrometry and imaging for determination of fipronil and its metabolites in food and biological samples

Gold nanoparticles (AuNPs) represent an attractive inorganic matrix for laser desorption/ionization mass spectrometry (LDI-MS) detection of low-molecular-weight analytes; however, their direct use is hindered by severe aggregation. To limit AuNPs aggregation, hexagonal boron nitride nanosheets (h-BNNs) were employed as supports to improve their desorption/ionization efficiency. Thus, Au@BN was synthesized and systematically characterized. It showed low background noise and high sensitivity for LDI-MS of fipronil and its metabolites. Au@BN-assisted LDI-MS was validated using complex samples including blueberry juice, green tea beverage, and fish muscle, achieving low detection limits (0.05-0.20 µg·L^-1 for liquid media, 0.82-1.25 ng·g^-1 for fish muscle), wide linear ranges (0.2-100 µg·L^-1 for liquid media, 3.00-1000 ng·g^-1 for fish muscle), high reproducibility (7.55%-13.7%), and satisfactory recoveries (82.62%-109.1%). Furthermore, spatial distributions of analytes in strawberries and zebrafish were successfully imaged. This strategy allows for the quantitative analysis of other small molecules in complex substrates.

Determination of phthalate esters in bottled beverages by direct immersion solid phase microextraction with a porous boron nitride coated fiber followed by gas chromatography-mass spectrometry

A porous boron nitride with a large surface area was synthesized by one step grinding method with melamine, urea and boric acid as the precursors. The prepared porous boron nitride was used as the fiber coating material for the solid-phase microextraction of seven phthalate esters (diethylphthalate, diallyl phthalate, diisobutyl phthalate, dibutyl phthalat, butylbenzyl phthalate, dicyclohexyl phthalate and di-2-ethylhexylphthalate) prior to their gas chromatography-mass spectrometric detection. The important experimental parameters including the extraction time, extraction temperature, salt concentration, and stirring rate were optimized by both single factor and central composite design methods. Under the optimized experimental conditions, the linear response range for the analytes was from 0.030 to 30.0 μg L^-1 , and the limits of detection were from 0.010 to 0.040 μg L^-1 , respectively. The relative recoveries of the analytes for spiked samples at two concentration levels were 83.0%-109% with the relative standard deviations less than 12%. The established method was successfully applied for the determination of the phthalate esters in bottled juice beverage samples. This article is protected by copyright. All rights reserved.

In-situ fabrication of a chlorine-functionalized covalent organic framework coating for solid-phase microextraction of polychlorinated biphenyls in surface water

The functionalization of covalent organic frameworks (COFs) identifies significant potential for developing selective coating materials for solid-phase microextraction (SPME). Herein, a chlorine-functionalized covalent organic framework (CF-COF) was in-situ synthesized by employing triformylphloroglucinol (Tp) and 2,5-dichloro-1,4-phenylenediamine (2,5-DCA) as monomers on an amino-functionalized stainless steel wire. The obtained CF-COF coated fiber exhibited a higher enrichment capacity for polychlorinated biphenyls (PCBs) than commercial fibers and non-chlorinated COF fiber, owing to a more hydrophobic surface, size-matching effect, a large number of micropores and the π-π stacking interactions between COF coating and analytes. As a practical application, the CF-COF coated fiber was applied to the headspace extraction of 17 PCBs prior to their quantification by GC/MS. The established analytical method offered a good linearity in the range of 0.1-1000 ng L^-1, low detection limits of 0.0015-0.0088 ng L^-1, and satisfactory enhancement factors (EFs) of 699-4281. The repeatability for single fiber and the fiber-to-fiber reproducibility was lower than 9.26% and 9.33%, respectively. The proposed method was verified to be sensitive, selective, and applicable for the analysis of ultra-trace PCBs in environmental surface water samples with the recoveries ranged from 78.7% to 124.0%.

Sample bottle coated with sorbent as a novel solid-phase extraction device for rapid on-site detection of BTEX in water

Solid-phase extraction (SPE) is a popular technique for environmental sample pretreatment. However, SPE usually requires complex sample pretreatment processes, which is time-consuming and inconvenient for real-time and on-site monitoring. Herein, a solvent-free, rapid, and user-friendly SPE device was developed by coating the polydimethylsiloxane (PDMS)/divinylbenzene (DVB) sorbent on the inner wall of a sample bottle. The extraction process and desorption process were both carried out in the bottle. The analytes trapped in the sorbent were thermally desorbed and simultaneously sucked out from the bottle by an air sampling tube equipped on field-portable GC-MS. Different to previous work, the sample pretreatment process didn't require any complicated and time-consuming steps, such as centrifugation or filtration. The total analysis time for each sample was less than 25 min, which was feasible for rapid on-site detection, and thus avoided the losses and contamination of samples in conventional sample storage and transportation processes. Under optimal conditions, the proposed SPE method exhibited wide linear ranges, low detection limits (0.010-0.036 μg L^-1, which were much lower than the maximum levels restricted by the US Environmental Protection Agency and the Chinese GB3838-2002 standard), good intra-bottle repeatability (6.13-7.17%, n = 3) and satisfactory inter-bottle reproducibility (4.73-6.47%, n = 3). Finally, the method was successfully applied to the rapid detection of BTEX in the field. The recoveries of BTEX in spiked water samples ranged from 89.1% to 116.2%. This work presents a novel SPE approach for rapid on-site monitoring in water samples.

Boron nitride modified reduced graphene oxide as solid-phase microextraction coating material for the extraction of seven polycyclic aromatic hydrocarbons from water and soil samples

A novel hexagonal boron nitride modified reduced graphene oxide material was synthesized and used as the adsorbent for the solid-phase microextraction of seven polycyclic aromatic hydrocarbons from water and soil samples prior to their detection by gas chromatography-flame ionization detector. Under optimal conditions, the linear response range of the analytes for water sample is 0.25-50 ng/mL with the correlation coefficients (r) ranging between 0.9953 and 0.9996. The linear range for soil sample is 1.0-400 ng/g with r ranging from 0.9959 to 0.9999. On the basis of the signal-to-noise ratio of 3, the limits of detections for the analytes ranged from 0.05 to 0.15 ng/mL for water samples, and from 0.3 to 0.5 ng/g for soil samples. The relative recoveries of the seven polycyclic aromatic hydrocarbons for water and soil samples were in the range of 79.55-120.0 and 78.76-120.8%, respectively. The relative standard deviations for the determination of the analytes in water and soil samples were lower than 11 and 10%, respectively. The method is simple and suitable for the determination of polycyclic aromatic hydrocarbon residues in water and soil samples.

Magnetic boron nitride nanosheets as a novel magnetic solid-phase extraction adsorbent for the determination of plant growth regulators in tomatoes

A novel magnetic boron nitride nanosheets (Fe₃O₄@BNNSs) composite-based magnetic solid-phase extraction (MSPE) method was employed to analyse six plant growth regulators (PGRs) in tomatoes combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The novel Fe₃O₄@BNNSs composite was prepared via an in situ chemical coprecipitation process and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). Several factors that may affect the extraction efficiencies were optimized. Under the optimal factors, low limits of detection (0.002-0.010 ng g^-1), good linear ranges (0.05-10 ng g^-1) and satisfactory precisions (intra-day: 1.2%-3.9%; inter-day: 2.1%-6.9%) were achieved. The established approach was successfully employed to extract and determine PGRs in tomatoes, and the spiked recoveries were between 85.2 and 109.0%.

Fully automated graphitic carbon nitride-based disposable pipette extraction-gas chromatography-mass spectrometric analysis of six polychlorinated biphenyls in environmental waters

A fully automated online emulsification-enhanced disposable pipette extraction-gas chromatography-mass spectrometry (EE-DPX-GC-MS) method has been developed for the extraction of six polychlorinated biphenyls (PCBs) from environmental waters. An in-house prepared material, graphitic carbon nitride (g-C₃N₄), was used as sorbent in a home-packed DPX device. The six PCBs studied include PCB 10, 28, 52, 153, 138 and 180. g-C₃N₄ was characterized successfully by X-ray diffraction, elemental analysis, scanning electron microscopy, Fourier-transform infrared and Raman spectroscopy. As a C-N analogue of graphite, the two-dimensional structure of g-C₃N₄ allows rapid analyte adsorption and desorption to take place. With a significant number of nitrogen functionalities in g-C₃N₄, the material dispersed well in aqueous sample, increasing the active surface area of contact between the sorbent and the sample. When coupled with a pre-emulsification step, PCBs in each portion of sample could be efficiently extracted by g-C₃N₄ within 20 s of gentle turbulence. Under the most favorable conditions, the automated online EE-DPX-GC-MS method achieved wide dynamic working ranges with good linearity (r² ≥ 0.998) for all analytes. Limits of detection ranging between 4.35 and 7.82 ng L^-1 were attained, with enrichment factors of between 34 and 57 and relative standard deviations (RSDs) for intra- and inter-day precision of ≤ 8.95% and ≤ 12.6%, respectively. Absolute recoveries were between 69.3% and 109%. The fully automated online EE-DPX-GC-MS approach was applied to industrial wastewaters and reservoir waters where good relative recoveries of PCBs of between 89.3% and 105% were obtained, with RSDs ≤ 11.6%.

Evaluation of a mixed anionic-nonionic surfactant modified eggshell membrane as an advantageous adsorbent for the solid-phase extraction of Sudan I-IV as model analytes

The coadsorption of mixed anionic-nonionic surfactants, sodium dodecylbenzenesulfonate with Triton X-100, on the surface of eggshell membrane was investigated based on adsorption isotherms to improve the solid-phase extraction performance of eggshell membrane toward organic contaminants. Results showed that even though excess Triton X-100 might inhibit the adsorption of sodium dodecylbenzenesulfonate, a low dosage of Triton X-100 can significantly improve sodium dodecylbenzenesulfonate modification and enhance the extraction efficiency of eggshell membrane from 73.7 to 100.4% because of the formation of mixed hemimicelles. The highest recovery was achieved at 2:8 (Triton X-100/sodium dodecylbenzenesulfonate mass ratios), and multiple mechanisms involving π-π interactions, hydrophobic effect, and π-π electron donor-acceptor interactions contributed to the strong extraction affinity. When mixed, the Triton X-100 and sodium dodecylbenzenesulfonate modified eggshell membrane packed cartridge coupled with high-performance liquid chromatography was applied for the simultaneous determination of trace Sudan I-IV, and low detection limits (0.16-0.26 ng/L) were achieved with satisfactory linearity (R²  > 0.999) in 10-10 000 μg/L. For real samples, Sudan II and III in one chilli sauce sample were found at 4.3 and 1.7 μg/kg. Sudan I-IV recoveries at three spiked levels were 87.4-102.9% with precisions <6.8%. Comparison with commonly used solid-phase extraction adsorbents and methods further reflected the superiorities of the proposed adsorbent in sensitivity, retention ability, and applicability.