Three dimensionally honeycomb layered double hydroxides framework as a novel fiber coating for headspace solid-phase microextraction of phenolic compounds

A novel top-down strategy for in situ construction of vertically oriented hexagonal NiCr LDHs nanosheet arrays with intercalated sulfate ions on Nichrome fiber for selective solid-phase microextraction of phenolic compounds in water samples

BACKGROUND

Phenolic compounds (PCs) are a class of polar aromatic pollutants with high toxicity in environmental water. Generally the efficient sample preparation is essential for the quantification of ultra-trace target PCs in real water sample before appropriative instrumental analysis. SPME is a convenient, solvent-free and time-saving miniaturized technique and has been recognized as a green alternative to conventional extraction techniques. In SPME, however, commercial fused-silica fibers are limited to the fragility, operation temperature, extraction capacity and selectivity as well as lifetime. Therefore, the development of new SPME fibers is always needed to overcome such limitations.

RESULTS

We presented a novel top-down strategy for in situ construction of vertically oriented hexagonal sulfate intercalated NiCr layered double hydroxide nanosheet arrays (NiCr LDHs-SO4 NSAs) on the Nichrome (NiCr) substrate by hydrothermal treatment in NaOH solution containing (NH4)2S2O8. The results showed that much shorter hydrothermal time was needed for the construction of NiCr@NiCr LDHs-SO4 NSAs fiber in the presence of (NH4)2S2O8. Moreover, the unique NiCr LDHs-SO4 NSAs coating offered open access structure, and thereby more available surface area for adsorption. The resulting fiber exhibited better extraction efficiency for phenolic compounds (PCs), faster mass transfer rate, higher mechanical stability, and longer service life than original NiCr@NiCr LDHs NSs fiber and typical commercially fused-silica fibers. After optimizing conditions, the SPME-HPLC-UV method demonstrated a linear range from 0.05 μg L-1 to 200 μg L-1 with LODs of 0.015-0.156 μg L-1 (S/N = 3) and LOQs of 0.048-0.498 μg L-1 (S/N = 10), as well as good repeatability (3.06%-5.22%) and fiber-to-fiber reproducibility (4.32%-6.49%).

SIGNIFICANCE

The developed SPME-HPLC-UV method with the constructed fiber was applied to the preconcentration and detection of different types of PCs in real water samples, showing satisfactory recoveries ranging from 86.20% to 107.8% with RSDs of 3.18%-6.69%. This study provides a new strategy for in situ construction of bimetallic hydroxides and their derived nanocomposite coatings on the NiCr fiber substrate in practical SPME application.

Applications of porous frameworks in solid-phase microextraction

Porous frameworks are a term of attracting solid materials assembled by interconnection of molecules and ions. These trendy materials due to high chemical and thermal stability, well-defined pore size and structure, and high effective surface area gained attention to employ as extraction phase in sample pretreatment methods before analytical analysis. Solid-phase microextraction is an important subclass of sample preparation technique that up to now different configurations of this method have been introduced to get adaptable with different environments and analytical instruments. In this review, theoretical aspect and different modes of solid-phase microextraction method are investigated. Different classes of porous frameworks and their applications as extraction phase in the proposed microextraction method are evaluated. Types and features of supporting substrates and coating procedures of porous frameworks on them are reviewed. At the end, the prospective and the challenges ahead in this field are discussed.

In-situ formation of Zn-Al layered double oxides on electrochemically anodized nanoporous aluminum film as sorbent for chlorophenols extraction from water and wastewater followed by determination using HPLC

Herein, we present a simple, cost-effective, and robust strategy for the in-situ preparation of Zn-Al layered double oxides-anodized aluminum thin film via a facile hydrothermal method, followed by calcination treatment of the Zn-Al layered double hydroxide in the air atmosphere. The in-situ prepared Zn-Al layered double oxide-anodized aluminum film was implemented as sorbent for thin film microextraction of four selected chlorophenols (4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol), followed by high-performance liquid chromatography-ultraviolet detection. The different variables of the thin film microextraction were screened via Plackett-Burman design and then optimized through Box-Behnken design. Under the optimum condition, the method showed good linear ranges (0.2-200 μg/L) with the coefficient of determinations higher than 0.9938. The calculated limit of detections were between 0.07 and 0.56 μg/L. Relative standard deviations of the method for determination of the analytes at 5 μg/L concentration level (n = 3) were ranged from 3.5 to 3.9% (as interday). The enrichment factors were between 39 and 58. This extraction method was demonstrated to be fast, efficient, and convenient. To study the capability of the developed method for real sample analysis, tap, well, river, and two types of wastewater samples were satisfactorily analyzed.

In-syringe extraction using compressible and self-recoverable, amphiphilic graphene aerogel as sorbent for determination of phenols

Graphene aerogels (GAs) have demonstrated great promise as sorbent materials. However, the intrinsically hydrophobic GAs are unsuitable for extraction of highly water-soluble analytes. Moreover, lack of compressibility limits the recyclability of GAs. In this work, an interesting type of water-induced self-recoverable amphiphilic GA was synthesized and employed as sorbent to extract nine priority phenols, listed as priority pollutants by the United States Environmental Protection Agency, from aqueous samples. The water-induced self-recoverability gives the GA the characteristic of a sponge, providing high recyclability and long-life. The aerogel was placed in a 2-mL microsyringe for in-syringe extraction of the phenols. The GA exhibits amphiphilicity due to the cross-linking by polyvinyl alcohol. At the same time, it exhibited selectivity to the water-soluble phenols. The extracted phenols were eluted with acetonitrile from the GA and the final extract was analyzed by high-performance liquid chromatography with ultraviolet detection (HPLC-UV). The results showed that this method provided low limits of detection for the phenols (0.089-0.015 µg/L), good linearity (r² ≥ 0.9956) and low relative standard deviations (≤6.8%). The optimized method was applied successfully to river water samples. The simple in-syringe extraction procedure in combination with HPLC-UV analysis was demonstrated to be efficient, fast and convenient.

Utilizing a novel sorbent in the solid phase extraction for simultaneous determination of 15 pesticide residues in green tea by GC/MS

Pesticide residues exceeding standard in green tea is a widespread problem of the world's attention, containing organochlorine pesticides (OCPs), organophosphorus pesticides (OPPs), and pyrethroids. In this research, three dimensionally honeycomb Mg-Al layered double oxide (TDH-Mg-Al-LDO) combined with graphitized carbon black (GCB), packed as a column, was used as a novel solid phase extraction sorbent, applying in simultaneous determination of 15 pesticide residues in green tea coupled with GC-MS. Compared with different type of SPE column, it showed that TDH-Mg-Al-LDO exhibited great advantages in the extraction of 15 pesticide residues from green tea, which was seldom reported before. Different experiment conditions, such as combination order of Mg-Al-LDO and GCB, dosage of sorbents, type and volume of eluting solvent were thoroughly studied and optimized. The limits of detection (LODs) of 15 pesticides ranged from 0.9 to 24.2ng/g and the limits of quantifications (LOQs) were ranging from 3.0 to 80.0ng/g. The recoveries using this method at three spiked concentration levels (10, 100 and 500ng/g for Fenthion, P,P'-DDE, O,P'-DDT, P,P'-DDD and Bifenthrin, 100, 500 and 2000ng/g for the others) range from 71.1 to 119.0%. The relative standard deviation (RSD) was from 0.1 to 7.6% in all case. The result indicated that the proposed analytical method had been successfully applied for the simultaneous determination of 15 pesticide residues in commercial green tea.

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.