Oxidized multiwalled carbon nanotubes as a novel solid-phase microextraction fiber for determination of phenols in aqueous samples

A novel Schiff base network-1 nanocomposite coated fiber for solid-phase microextraction of phenols from honey samples

A novel covalent organic framework, Schiff base network-1 (SNW-1), was synthesized and used as a solid-phase microextraction (SPME) fiber coating material. The SNW-1 coated SPME fiber was fabricated by a covalent chemical cross-linking between the SNW-1 nanocomposite and a silanol-functionalized stainless steel wire substrate. Scanning electron microscopy and nitrogen isothermal adsorption results indicate that the new fiber coating exhibited a porous, homogenous surface with the Brunauer-Emmett-Teller surface of 668m²g^-1. The prepared fiber was explored for the SPME of phenols from honey samples prior to their determination by gas chromatography-mass spectrometry. The developed method had large enrichment factors (136-816), low limits of detection (0.06-0.2ngg^-1), good linearity (0.1-100.0ngg^-1) and repeatability (<9.7%) for phenols. The recoveries for spiked phenols (1.0ngg^-1 and 10.0ngg^-1) in Wolfberry, Robinia and Codonopsis honey samples were in the range of 84.2-107.2% with the relative standard deviations ranging from 3.8% to 12.7%. The developed method was suitable for the determination of phenols from honey samples.

Highly selective and effective solid phase microextraction of benzoic acid esters using ionic liquid functionalized multiwalled carbon nanotubes-doped polyaniline coating

The present work reports the electrochemical fabrication of an ionic liquid functionalized multiwalled carbon nanotubes-polyaniline (MWCNT@IL/PANI) nanocomposite coating and its application in the headspace-solid phase microextraction (HS-SPME) and gas chromatography (GC) determination of benzoic acid esters (i.e., methyl benzoate, ethyl benzoate, propyl benzoate and butyl benzoate). The MWCNTs was firstly functionalized with amine-terminated IL (MWCNT@IL) through chemical reduction, and then was doped in PANI during the electropolymerization of aniline. The resulting coating was characterized by infrared spectroscopy, field emission scanning electron microscopy and thermo gravimetry. It showed net-like structure and had high thermal stability (up to 330°C). Furthermore, it presented high selectivity for the four benzoic acid esters and thus suited for their HS-SPME-GC determination. Results showed that under optimized extraction conditions, the detection limits were less than 6.1ngL(-1) (S/N=3) and the linear detection ranges were 0.012-50μgL(-1) (R≥0.9957) for these analytes. The relative standard deviations (RSDs) were lower than 6.4% for five successive measurements with one fiber, and the RSDs for fiber-to-fiber were 4.4-9.6% (n=5). The developed method was successfully applied to the determination of these benzoic acid esters in perfume samples.

Development of a carbon-nanoparticle-coated stirrer for stir bar sorptive extraction by a simple carbon deposition in flame

Stir bar sorptive extraction is an environmentally friendly microextraction technique based on a stir bar with various sorbents. A commercial stirrer is a good support, but it has not been used in stir bar sorptive extraction due to difficult modification. A stirrer was modified with carbon nanoparticles by a simple carbon deposition process in flame and characterized by scanning electron microscopy and energy-dispersive X-ray spectrometry. A three-dimensional porous coating was formed with carbon nanoparticles. In combination with high-performance liquid chromatography, the stir bar was evaluated using five polycyclic aromatic hydrocarbons as model analytes. Conditions including extraction time and temperature, ionic strength, and desorption solvent were investigated by a factor-by-factor optimization method. The established method exhibited good linearity (0.01-10 μg/L) and low limits of quantification (0.01 μg/L). It was applied to detect model analytes in environmental water samples. No analyte was detected in river water, and five analytes were quantified in rain water. The recoveries of five analytes in two samples with spiked at 2 μg/L were in the range of 92.2-106% and 93.4-108%, respectively. The results indicated that the carbon nanoparticle-coated stirrer was an efficient stir bar for extraction analysis of some polycyclic aromatic hydrocarbons.

Determination of ultra-trace amounts of chlorophenols in rain, tap and river water by an electrochemically controlled in-tube solid phase microextraction method

A nanostructured copolymer coating consisting of PPy doped with Naf was electrochemically synthesized on the inner surface of a stainless steel capillary tube. It was utilized to extract trace pollutants from water samples.

Highly photoluminescent pH-independent nitrogen-doped carbon dots for sensitive and selective sensing of p-nitrophenol

Highly photoluminescent pH-independent nitrogen-doped carbon dots prepared from maleic acid and ethylenediamine exhibit highly sensitive and selective sensing of p-nitrophenol.

A physical entrapment method for the preparation of carbon nanotube reinforced macroporous adsorption resin with enhanced selective extraction performance

In this paper, we demonstrate a novel carbon nanotube (CNT) reinforced macroporous adsorption resin (MAR) for the first time. The CNTs were dispersed in water via sonication, and then in situ physically entrapped in the pores of MAR by capillary forces and sonication. The resulting CNT reinforced MAR (CNT-MAR) was proved by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM), and subsequently applied to extract a mixture of 8 types, 14 natural products. For comparison, the extraction efficiency of original MAR without CNTs was also evaluated. After extraction, the supernatants were detected via high-performance liquid chromatography (HPLC). The results indicated that the introduction of carbon nanotubes (CNTs) into the pores of MAR can significantly improve the adsorptive selectivity of MAR for natural products. The original MAR without CNTs has almost the same adsorption capacity for selectively extracting 3 types of natural products (phenols, alkaloids and anthraquinones). However, the CNT-MAR only could selectively extract anthraquinones and the adsorption capacity for three anthraquinone natural products is 1.46-1.83 times higher than that of unmodified MAR. In order to achieve the highest extraction efficiency of CNT-MAR for anthraquinone natural products, the main extraction parameters such as the extraction time and the pH value were also optimized. The CNT-MAR demonstrated an excellent ability to extract anthraquinone natural products with high selectivity and adsorption capacity. Due to its low cost, easy preparation and use, and operational characteristics, it shows great potential for selective extraction of natural products.

Graphene oxide reinforced polymeric ionic liquid monolith solid-phase microextraction sorbent for high-performance liquid chromatography analysis of phenolic compounds in aqueous environmental samples

A graphene oxide reinforced polymeric ionic liquids monolith was obtained by copolymerization of graphene oxide doped 1-(3-aminopropyl)-3-(4-vinylbenzyl)imidazolium 4-styrenesulfonate monomer and 1,6-di-(3-vinylimidazolium) hexane bihexafluorophosphate cross-linking agent. Coupled to high-performance liquid chromatography, the monolith was used as a solid-phase microextraction sorbent to analyze several phenolic compounds in aqueous samples. Under the optimized extraction and desorption conditions, linear ranges were 5-400 μg/L for 3-nitrophenol, 2-nitrophenol, and 2,5-dichlorophenol and 2-400 μg/L for 4-chlorophenol, 2-methylphenol, and 2,4,6-trichlorophenol (R(2) = 0.9973-0.9988). The limits of detection were 0.5 μg/L for 3-nitrophenol and 2-nitrophenol and 0.2 μg/L for the rest of the analytes. The proposed method was used to determine target analytes in groundwater from an industrial park and river water. None of the analytes was detected. Relative recoveries were in the range of 75.5-113%.

New trends in sample preparation techniques for environmental analysis

Environmental samples include a wide variety of complex matrices, with low concentrations of analytes and presence of several interferences. Sample preparation is a critical step and the main source of uncertainties in the analysis of environmental samples, and it is usually laborious, high cost, time consuming, and polluting. In this context, there is increasing interest in developing faster, cost-effective, and environmentally friendly sample preparation techniques. Recently, new methods have been developed and optimized in order to miniaturize extraction steps, to reduce solvent consumption or become solventless, and to automate systems. This review attempts to present an overview of the fundamentals, procedure, and application of the most recently developed sample preparation techniques for the extraction, cleanup, and concentration of organic pollutants from environmental samples. These techniques include: solid phase microextraction, on-line solid phase extraction, microextraction by packed sorbent, dispersive liquid-liquid microextraction, and QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe).

A sensitive and efficient method for trace analysis of some phenolic compounds using simultaneous derivatization and air-assisted liquid-liquid microextraction from human urine and plasma samples followed by gas chromatography-nitrogen phosphorous detection

In present study, a simultaneous derivatization and air-assisted liquid-liquid microextraction method combined with gas chromatography-nitrogen phosphorous detection has been developed for the determination of some phenolic compounds in biological samples. The analytes are derivatized and extracted simultaneously by a fast reaction with 1-flouro-2,4-dinitrobenzene under mild conditions. Under optimal conditions low limits of detection in the range of 0.05-0.34 ng mL(-1) are achievable. The obtained extraction recoveries are between 84 and 97% and the relative standard deviations are less than 7.2% for intraday (n = 6) and interday (n = 4) precisions. The proposed method was demonstrated to be a simple and efficient method for the analysis of phenols in biological samples.

A novel molecularly imprinted polymer thin film at surface of ZnO nanorods for selective fluorescence detection of para-nitrophenol

A novel MIPs-based ZnO nanorods with molecular recognition ability for para-nitrophenol was successfully synthesized via a surface imprinting-directing polymerization.

Preparation and evaluation of a layered double hydroxide film on a nanoporous anodic aluminum oxide/aluminum wire as a highly thermal-resistant solid-phase microextraction fiber

A hierarchical layered double hydroxide framework on a nonporous anodic aluminum oxide/aluminum wire was used as a solid phase microextraction fiber for separation and determination of phenolic compounds.

Detection of organophosphorous pesticides in soil samples with multiwalled carbon nanotubes coating SPME fiber

A headspace solid phase microextraction (HS-SPME) technique using stainless steel fiber coated with 20 μm multi-walled carbon nanotubes (MWCNTs) and gas chromatography with thermionic specific detector (GC-TSD) was developed to determine organophosphorous pesticides (OPPs) in soil. Parameters affecting the extraction efficiency such as extraction time and temperature, ionic strength, the volume of water added to the soil, sample solution volume to headspace volume ratio, desorption time, and desorption temperature were investigated and optimized. Compared to commercial polydimethylsiloxane (PDMS, 7 μm) fiber, the PDMS fiber was better to be corrected as phorate, whereas the MWCNTs fiber gave slightly better results for methyl parathion, chlorpyrifos and parathion. The optimized SPME method was applied to analyze OPPs in spiked soil samples. The limits of detection (LODs, S/N = 3) for the four pesticides were <0.216 ng g(-1), and their calibration curves were all linear (r (2) ≥ 0.9908) in the range from 1 to 200 ng g(-1). The precision (RSD, n = 6) for peak areas was 6.5 %-8.8 %. The recovery of the OPPs spiked real soil samples at 50 and 150 ng g(-1) ranged from 89.7 % to 102.9 % and 94.3 % to 118.1 %, respectively.

Development of a solid-phase microextraction fiber by the chemical binding of graphene oxide on a silver-coated stainless-steel wire with an ionic liquid as the crosslinking agent

Graphene oxide was bonded onto a silver-coated stainless-steel wire using an ionic liquid as the crosslinking agent by a layer-by-layer strategy. The novel solid-phase microextraction fiber was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman microscopy. A multilayer graphene oxide layer was closely coated onto the supporting substrate. The thickness of the coating was about 4 μm. Coupled with gas chromatography, the fiber was evaluated using five polycyclic aromatic hydrocarbons (fluorene, anthracene, fluoranthene, 1,2-benzophenanthrene, and benzo(a)pyrene) as model analytes in direct-immersion mode. The main conditions (extraction time, extraction temperature, ionic strength, and desorption time) were optimized by a factor-by-factor optimization. The as-established method exhibited a wide linearity range (0.5-200 μg/L) and low limits of determination (0.05-0.10 μg/L). It was applied to analyze environmental water samples of rain and river water. Three kinds of the model analytes were quantified and the recoveries of samples spiked at 10 μg/L were in the range of 92.3-120 and 93.8-115%, respectively. The obtained results indicated the fiber was efficient for solid-phase microextraction analysis.

Graphene coating bonded onto stainless steel wire as a solid-phase microextraction fiber

A graphene coating bonded onto stainless steel wire was fabricated and investigated as a solid-phase microextraction fiber. The coating was characterized by scanning electron microscopy and energy-dispersive X-ray spectrometer. The coating with rough and crinkled structure was about 1 μm. These characteristics were helpful for promoting extraction. Using five n-alkanes (n-undecane, n-dodecane, n-tridecane, n-tetradecane and n-hexadecane) as analytes, the fiber was evaluated in direct-immersion mode by coupling with gas chromatography (GC). Through optimizing extraction and desorption conditions, a sensitive SPME-GC analytical method was established. SPME-GC method provided wide linearity range (0.2-150 μg L(-1)) and low limits of determination (0.05-0.5 μg L(-1)). It was applied to analyze rain water and a soil sample, and analytes were quantified in the range of 0.85-1.96 μg L(-1) and 0.09-3.34 μg g(-1), respectively. The recoveries of samples spiked at 10 μg L(-1) were in the range of 90.1-120% and 80.6-94.2%, respectively. The fiber also exhibited high thermal and chemical stability, due to the covalent bonds between graphene coating and wire, and the natural resistance of graphene for thermal, acid and basic conditions.