MOF-199-based coatings as SPME fiber for measurement of volatile organic compounds in air samples: Optimization of in situ deposition parameters

Recent Trends in the Development of Green Analytical Sample Preparation Methods Using Advanced Materials

Recent concern about the impact of environmental preservation and the health of living beings has opened new avenues for scientific research. In this context, contemporary analytical chemistry has been marked by the development of green analytical methodologies, which aim to reduce the use of toxic reagents and minimize the environmental impact of analytical processes. Progress in this area involves the optimization of sample preparation techniques and the use of new functional materials, which contribute to a more sustainable and efficient analysis. Among these methodologies, miniaturized sample preparation techniques stand out, as they use smaller volumes of solvents and offer high sensitivity and selectivity. The use of advanced materials, such as molecularly imprinted polymers, MOFs, and conductive polymers, has driven innovation in analytical procedures regarding complex matrices, including environmental, food, and biological samples. These materials offer high selectivity and stability, improving efficiency in the extraction and detection of specific analytes. This review explores the integration of sustainable and green methodologies. It critically highlights applications and evaluates them using the Analytical Greenness Metric for Sample Preparation, based on publications from the past 6 years.

Saliva analysis using metal-organic framework-coated miniaturized vials

BACKGROUND

In-vial microextraction is probably the simplest microextraction technique because it eliminates centrifugation and/or filtration steps while offering short extraction and desorption times. However, it has had limited applicability, mostly involving polydimethylsiloxane coatings and gas chromatography applications. Quite recently, one study introduced metal-organic framework (MOF)-coated glass vials for environmental analyses and liquid chromatography, thus combining the advantages of MOFs as adsorbents with the advantages of the in-vial approach, while not limiting the application to volatile analyses. Besides, a much higher exposure of the MOF to the sample due to the thin film coating available within the vial's inner walls is attained. Clearly, the applicability of this format for bioanalysis has not been evaluated, as there are not many stable and reusable sorbents useful for biological samples presenting high protein content. Besides, the in-vial technique must demonstrate to be valid for low-availability samples, such as saliva.

RESULTS

A vial with 2 mL-capacity and coated uniformly with a MOF has been developed to analyze saliva in a thin film solid-phase microextraction approach, while keeping an adequate analytical performance using only 50 μL of solvent for desorption. The procedure only requires 12.5 min of operation. Interestingly, the issues related to pore-blocking of the crystalline materials by proteins present in the saliva samples are solved with a simple cleaning protocol that also ensures a high reusability of the vials (more than 50 times). Seven bisphenols were determined in saliva with these devices, reaching limits of detection down to 0.10 μg L-1, and with inter-vial and inter-day precision values as RSD (in %) lower than 15% at a low concentration level (2.0 μg L-1).

SIGNIFICANCE

A device is presented to analyze complex saliva samples with a novel miniaturized MOF-coated vial ensuring proper reusability, while addressing the challenge of protein clogging and, at the same time, keeping adequate analytical performance with short analysis times. This approach represents significant progress in the bioanalytical sample preparation field, particularly when using sorbent porous materials integrated within miniaturized devices.

Recent advances in solid phase microextraction with various geometries in environmental analysis

Solid phase microextraction (SPME) has emerged as a versatile sample preparation technique for the preconcentration of a broad range of compounds with various polarities, especially in environmental studies. SPME has demonstrated its eco-friendly credentials, significantly reducing the reliance on solvents. The use of biocompatible materials as a coating recipe facilitates the acceptance of SPME devices in analytical chemistry, primarily in the monitoring of environmental pollutants such as persistent organic pollutants (POPs), volatile organic compounds (VOCs), and pesticides from the various environmental matrices. During the last few years, investigators have reported an improvement in the SPME enrichment technique after changing the coating recipe, geometries, and sampling procedure from the complex matrices. Furthermore, the development of various geometries of SPME with large surface areas has enhanced the extraction efficiency of environmental pollutants. As a miniaturized sample preparation technique, SPME significantly reduces the solvent usage, suggesting a potential platform for green chemistry-based research for water, air, and soil analysis. This review article summarizes the evolution of SPME, its various modes, the application of SPME, recent innovations, and prospects for the determination of water, air, and soil pollution. The advantages and disadvantages of SPME in comparison to other extraction techniques have been discussed here. This review serves as a valuable resource for investigators working in sustainable environmental research.

Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis

Solid-phase microextraction (SPME) has been widely proposed for the extraction, clean-up, and preconcentration of analytes of environmental concern. Enrichment capabilities, preconcentration efficiency, sample throughput, and selectivity in extracting target compounds greatly depend on the materials used as SPME coatings. Supramolecular materials have emerged as promising porous coatings to be used for the extraction of target compounds due to their unique selectivity, three-dimensional framework, flexible design, and possibility to promote the interaction between the analytes and the coating by means of multiple oriented functional groups. The present review will cover the state of the art of the last 5 years related to SPME coatings based on metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular macrocycles used for environmental applications.

Enhanced adsorption of toluene on thermally activated ZIF-67: Characterization, performance, and modeling insights

The zeolitic imidazolate framework-67 (ZIF-67) has been explored for the dynamic adsorption of toluene vapor. We synthesized ZIF-67 through a straightforward room-temperature process and characterized it using XRD, FT-IR, DLS, and SEM techniques. The synthesized ZIF-67 possessed a Brunauer-Emmett-Teller (BET) surface area of 1578.7 m2/g and 0.76 μm particle size. Thermal activation under various conditions revealed that ZIF-67, activated in dry air at 250 °C, demonstrated optimal adsorption efficacy. Its adsorption capacity, time of breakthrough, and time of equilibration were 414.5 mg/g, 420 min, and 795 min, respectively. We investigated the impact of diverse operational parameters on adsorption through breakthrough curve analysis. An increase in the toluene concentration from 100 to 1000 ppm enhanced the adsorption capacity from 171 to 414 mg/g, while breakthrough time decreased from 1260 min to 462 min, respectively. Our findings show that increasing relative humidity from 0 to 70 % reduced 53.7 % in adsorption capacity and 46.3 % in breakthrough time. The competitive adsorption of toluene and ethylbenzene revealed that ZIF-67 had a higher selectivity for toluene adsorption. A 98 % adsorbent's regeneration efficiency at the first cycle reveals its reusability. The experimental data were successfully fitted to the Yan, Thomas, and Yoon-Nelson models to describe the adsorption process. The statistical validation of the model parameters confirms their reliability for estimating adsorption parameters, thus facilitating the design of fixed-bed adsorption columns for practical applications.

Structural and compositional analysis of MOF-derived carbon nanomaterials for the oxygen reduction reaction

The development of low-cost and efficient cathode catalysts is crucial for the advancement of fuel cells, as the oxygen reduction reaction (ORR) on the cathode is constrained by expensive commercial Pt/C catalysts and a significant energy barrier. Metal-organic frameworks (MOFs) are considered excellent precursors for synthesizing carbon nanomaterials due to their simple synthesis, rich structure and composition. MOF-derived carbon nanomaterials (MDCNM) inherit the morphology of their precursors at low dimensional scales, providing abundant edge defects, larger specific surface area, and excellent electron transport paths. Furthermore, the rich composition of MOFs enables the carbon nanomaterials derived from them to exhibit various physicochemical properties, including stronger electron gaining ability, oxygen affinity, and a higher degree of graphitization, resulting in excellent ORR activity. However, a more detailed analysis is necessary to understand the advantages and mechanisms of MDCNM in the field of the ORR. This review classifies and summarizes the structure and different chemical compositions of MDCNM in low dimensions, and provides an in-depth analysis of the reasons for their improved ORR activity. Additionally, the recent practical applications of MDCNM as cathode material in fuel cells are introduced and analyzed in detail, with a focus on the enhanced electrochemical performance.