Stirred discs from polycaprolactone nanofibers highly doped with graphene for straightforward preconcentration of pollutants in environmental waters

A novel sorbent for solid phase extraction (SPE) based on hybrid nanofibrous polycaprolactone containing graphene nanoparticles has been prepared. The preparation of hybrid polymer nanofibers with a very high 1:1 polymer/graphene ratio was achieved for the first time using alternating current electrospinning. The final appearance of these nanofibers was a thick porous layer that was cut into the shape of easy-to-handle extraction discs. Based on the preliminary study in which the graphene content varied, 30% graphene-doped nanofibers (w/w) exhibited the highest recoveries and enabled a significant increase in the retention of analytes, 2-25 times in comparison to PCL. The incorporation of graphene resulted in a higher surface area of 12 g/m2 compared to 2 g/m2 determined for the native polycaprolactone (PCL) nanofibers. This unique material was applied for a simple stirred disc sorptive extraction and preconcentration of trace levels of emerging organic environmental contaminants, bisphenols A, AF, AP, C, S, Z, 3-chlorophenol, and pesticides fenoxycarb, deltamethrin, and kadethrin from surface waters prior to HPLC-DAD determination. This was accomplished by stirring the unsupported nanofiber disc in a large-volume sample with RSD of five extractions of 3-15%. Recoveries yielded 87-120%, except 52% for bisphenol S due to its high polarity. Optimization of the extraction procedure included conditioning, sample volume, extraction time, and elution solvent. Our novel desorption procedure carried out in a vial used for the direct injection into the HPLC system significantly reduced sample handling and minimized potential human error.

A new approach of magnetic field application in miniaturized pipette-tip extraction for trace analysis of four synthetic hormones in breast milk samples

Herein, a novel homemade electrical device was designed, including two pieces of external neodymium magnets, providing a reciprocating magnetic field to introduce a magnetic-assisted dispersive pipette-tip micro solid-phase extraction. To evaluate the performance efficiency of the proposed method, a novel magnetic calcined GO/SiO₂@Co-Fe nanocube sorbent was synthesized, filled into the pipette-tip, exposed to the reciprocating magnetic field, and applied for the preconcentration of some hormone therapy drugs in human biological matrices. The effective adsorption and desorption parameters were optimized using a rotatable central composite design and one-variable-at-a-time approaches. Under the optimized conditions, the target analytes' detection limits were found to be below 0.02 ng mL^-1. Moreover, the calibration curves were linear in the range of 0.03-500.00 ng mL^-1 (R² > 0.9966), with RSDs% less than 7.8 %. Eventually, the established method was applied to extract the analytes from breast milk samples, followed by LC-ESI-MS/MS analysis.

Selective extraction of synthetic cathinones new psychoactive substances from wastewater, urine and cocktail using dummy molecularly imprinted polymers

Dummy molecularly imprinted polymers (DMIPs) for selective extraction of five common synthetic cathinones (SCs) were prepared by bulk polymerization. DMIPs materials possessed narrow diameter distribution (30-60 µm) and large specific surface area (329.6 m² g^-1). Imprinting factors for cathinone, methcathinone, mephedrone, methylone and ethylone were 1.11-1.82. DMIPs could also quickly adsorb SCs from aqueous solutions within 5 min. Therefore, the materials were used as solid-phase extraction (SPE) sorbents to selectively extract five SCs in complex samples. An accurate and sensitive analytical method based on DMIPs-SPE combined with HPLC-MS/MS was established. Under optimal conditions, the established method showed low limits of detection (0.002-0.1 ng mL^-1), satisfactory recoveries (84.1-97.7%) and good repeatability (relative standard deviation (RSD) below 9%). The method was successfully verified using wastewater, urine and cocktail samples. Recoveries of SCs at three spiking levels were in the range of 75.1-98.6%, with RSD values below 7.0%. Compared with commercial sorbents, DMIPs showed better clean-up ability with matrix effect values of -24.1%-8.3% for all SCs in wastewater, urine and cocktail samples. Therefore, the developed DMIPs-SPE-HPLC-MS/MS strategy could be used as a specific and cost-effective method for sensitive determination of SCs in complex samples.

Graphene Oxide and Biomolecules for the Production of Functional 3D Graphene-Based Materials

Graphene and its derivatives have been widely employed in the manufacturing of novel composite nanomaterials which find applications across the fields of physics, chemistry, engineering and medicine. There are many techniques and strategies employed for the production, functionalization, and assembly of graphene with other organic and inorganic components. These are characterized by advantages and disadvantages related to the nature of the specific components involved. Among many, biomolecules and biopolymers have been extensively studied and employed during the last decade as building blocks, leading to the realization of graphene-based biomaterials owning unique properties and functionalities. In particular, biomolecules like nucleic acids, proteins and enzymes, as well as viruses, are of particular interest due to their natural ability to self-assemble via non-covalent interactions forming extremely complex and dynamic functional structures. The capability of proteins and nucleic acids to bind specific targets with very high selectivity or the ability of enzymes to catalyse specific reactions, make these biomolecules the perfect candidates to be combined with graphenes, and in particular graphene oxide, to create novel 3D nanostructured functional biomaterials. Furthermore, besides the ease of interaction between graphene oxide and biomolecules, the latter can be produced in bulk, favouring the scalability of the resulting nanostructured composite materials. Moreover, due to the presence of biological components, graphene oxide-based biomaterials are more environmentally friendly and can be manufactured more sustainably compared to other graphene-based materials assembled with synthetic and inorganic components. This review aims to provide an overview of the state of the art of 3D graphene-based materials assembled using graphene oxide and biomolecules, for the fabrication of novel functional and scalable materials and devices.

Electrospun Membrane for the Extraction of Acrylamide in Pet Food Samples

A simple microextraction procedure was developed using an electrospun nanostructured membrane to determine acrylamide in pet food samples. Polyvinyl chloride, polyvinyl alcohol, and polyvinyl alcohol/hydroxyethyl cellulose electrospun membranes were prepared and investigated as a sorbent to extract acrylamide. The characterization of the synthesized electrospun membrane was accomplished using field-emission scanning electron microscopy (FESEM). FESEM images showed uniform morphology and beadless nanofibers. Quantification was done by high-performance liquid chromatography with ultraviolet detection. A series of microextraction parameters were optimized before quantitative analysis of dry pet food samples. The calibration curve exhibited good linearity with a correlation coefficient of 0.996 across a 1–100 μg/kg concentration range. The recovery of acrylamide for pet food samples spiked with 5 and 10 μg/kg was in the range of 79.6–113.9 (n = 3). The intraday precision of the method was less than 12% for three replicated real spiked samples at the 5 μg/kg level. The results demonstrated that the electrospun nanostructured membrane has good extraction selectivity and minimal matrix effect with an enrichment factor of 180-fold.

Green Bioanalytical Applications of Graphene Oxide for the Extraction of Small Organic Molecules

Bioanalysis is the scientific field of the quantitative determination of xenobiotics (e.g., drugs and their metabolites) and biotics (e.g., macromolecules) in biological matrices. The most common samples in bioanalysis include blood (i.e., serum, plasma and whole blood) and urine. However, the analysis of alternative biosamples, such as hair and nails are gaining more and more attention. The main limitations for the determination of small organic compounds in biological samples is their low concentration in these matrices, in combination with the sample complexity. Therefore, a sample preparation/analyte preconcentration step is typically required. Currently, the development of novel microextraction and miniaturized extraction techniques, as well as novel adsorbents for the analysis of biosamples, in compliance with the requirements of Green Analytical Chemistry, is in the forefront of research in analytical chemistry. Graphene oxide (GO) is undoubtedly a powerful adsorbent for sample preparation that has been successfully coupled with a plethora of green extraction techniques. GO is composed of carbon atoms in a sp² single-atom layer of a hybrid connection, and it exhibits high surface area, as well as good mechanical and thermal stability. In this review, we aim to discuss the applications of GO and functionalized GO derivatives in microextraction and miniaturized extraction techniques for the determination of small organic molecules in biological samples.