Progress in pre-treatment and extraction of organic and inorganic pollutants by layered double hydroxide for trace-level analysis

Continuous release of pollutants into the environment poses serious threats to environmental sustainability and human health. For trace-level analysis of pollutants, layered double hydroxide (LDH) is an attractive option to impart enhanced sorption capability and sensitivity toward pollutants because of its unique layered structure, tunable interior architecture, high anion-exchange capacities, and high porosity (e.g., Zn/Cr LDH/DABCO-IL, Ni/Al LDH, CS-Ni/Fe LDH, SDS-Fe₃O₄@SiO₂@Mg-Al LDH, Boeh/Mg/Al LDH/pC, and Fe@NiAl LDH). In concert with the well-defined analytical methodologies (e.g., HPLC and GC), the LDH materials can be employed to detect trace-level targets (e.g., as low as ∼ 20 fg/L for phenols) in aqueous environments. This review highlights LDH as a promising material for pre-treatment of a variety of organic and inorganic target pollutants in complex real matrices. Challenges and future requirements for research into LDH-based analytical methods are also discussed.

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.

Layered double hydroxide/poly(vinylpyrrolidone) coated solid phase microextraction Arrow for the determination of volatile organic compounds in water

Today, wide variety of adsorbents have been developed for sample pretreatment to concentrate and separate harmful substances. However, only a few solid phase microextraction Arrow adsorbents are commercially available. In this study, we developed a new solid phase microextraction Arrow coating, in which nanosheets layered double hydroxides and poly(vinylpyrrolidone) were utilized as the extraction phase and poly(vinyl chloride) as the adhesive. This new coating entailed higher extraction capacity for several volatile organic compounds (allyl methyl sulfide, methyl propyl sulfide, 3-pentanone, 2-butanone, and methyl isobutyl ketone) compared to the commercial Carboxen 1000/polydimethylsiloxane coating. Fabrication parameters for the coating were optimized and extraction and desorption conditions were investigated. The validation of the new solid phase microextraction Arrow coating was accomplished using water sample spiked with volatile organic compounds. Under the optimal conditions, the limits of quantification for the five volatile organic compounds by the new solid phase microextraction Arrow coating and developed gas chromatography with mass spectrometry method were in the range of 0.2-4.6 ng/mL. The proposed method was briefly applied for enrichment of volatile organic compounds in sludge.

A simple strategy based on fibers coated with surfactant-functionalized multiwalled carbon nanotubes to improve the properties of solid-phase microextraction of phenols in aqueous solution

Methods and experiments

In this study, a functionalized multiwalled carbon nanotube (MWCNT)-coated solid-phase microextraction (SPME) fiber was developed for concentrating analytes in aqueous samples. Sodium deoxycholate (NaDC) was used as a dispersing agent for non-covalent modification of MWCNTs. The coating showed porous structure and large adsorption capacity. To investigate the capability of this MWCNTs/NaDC SPME fiber, it was applied to the analysis of phenols in aqueous solution. After extraction, the analytes were desorbed in an acetonitrile–water solution and analyzed using high-performance liquid chromatography.

Results

The MWCNTs/NaDC fiber exhibited good analytical performance, and fine preparation reproducibility was obtained with the relative standard deviations (RSDs) ranging from 4.9% to 10.2% (n = 6) in one batch, from 5.7% to 11.9% (n = 3) among different batches. Under the optimum extraction conditions, the detection limits were 0.15–0.30 ng/mL(S/N = 3), the linear detection ranges were 1–100 ng/mL (R² ≥ 0.9997) for these analytes, and good recoveries (80.3–95.4%) were obtained for the spiked samples.

Conclusion

This is a simple and accurate pretreatment method for the analysis of phenols in aqueous samples.

Carbon nanotube/layered double hydroxide nanocomposite as a fibre coating for determination the essential oils of Achillea eriophora DC with the headspace solid-phase microextraction

The present study was conducted to synthesise a carbon nanotube/layered double hydroxide nanocomposite by an in situ growth route via electrostatic force. The fabricated carbon nanotube/layered double hydroxide nanocomposite was successful in deposition on a stainless-steel wire for the preparation of the solid-phase microextraction fibre. The produced fibers are enduring with high suitability being chemically and thermally stable capable of coupling to GC and GC/MS. The important extraction parameters including extraction temperature, extraction time, sample mass and added water were simultaneously optimised using an optimisation approach. I comparison to hydrodistillation (HD), headspace single drop micro-extraction) HS-SPME (is advantageous regarding little sample level, time-efficiency, convenience and low cost.

Preparation and characterization of an aptamer-functionalized solid-phase microextraction fiber and its application in the selective monitoring of adenosine phosphates with liquid chromatography and tandem mass spectrometry

An aptamer with adenosine triphosphate as a ligand was immobilized onto the surface of a porous-polymer-coated fiber to obtain an aptamer-functionalized porous-polymer-coated solid-phase microextraction fiber. The fiber was observed with a crosslinked and porous morphological surface structure. It shows specific selectivity to adenosine triphosphate with a selectivity coefficient of 22.1 compared to the scrambled oligonucleotide functionalized fiber, and the selectivity factors over other analogues and reference compounds were from 6.1 to 77.5. When the fiber-based solid-phase microextraction was coupled with liquid chromatography and tandem mass spectrometry, detection limits of 2.7, 29, and 34 μg/L were achieved for adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate, respectively. The spiking recoveries of 77.6-91.9% were achieved for trace adenosine phosphates in human serum sample. Furthermore, the fibers showed high stability and good reusability and could be used over 50 times for the real serum sample pretreatment without remarkable performance reduction.