Thermoanalytical Techniques Research Articles

Energetic Salts of Cubane-1,4-Dimethylnitrocarbamate.

Several salts of cubane-1,4-dimethylnitrocarbamate (CMNC) were synthesized. The divalent CMNC is deprotonated by alkaline, alkaline earth metal, and nonmetal bases to form the corresponding salts. The compounds were characterized and analyzed by multinuclear NMR and IR spectroscopy, mass spectrometry, elemental analysis, single crystal X-ray, and thermoanalytical techniques. The energies of formation for the salts were calculated using Gaussian. Detonation performances were calculated with the Explo5 (V6.03) computer code. The sensitivities toward impact and friction were determined and compared to the neutral CMNC.

Liquid crystalline polyurethane/POSS hybrid nanocomposites pyrolysis studies by Py-GC/MS and TG/FTIR techniques

The process of pyrolysis of liquid crystalline polyurethane (LCPU) composites with polyhedral oligomeric silsesquioxanes (POSS) has been studied using pyrolysis - gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetry/Fourier transform infrared spectroscopy (TG/FTIR) coupled thermoanalytical techniques. LCPU elastomers modified with POSS molecules with different architectures, bearing aromatic, isobutyl and cycloaliphatic moieties, yield various volatile products of pyrolysis that were collected and characterized. The TG study showed significant differences in the thermal behavior of composites studied, evidencing the influence of the silsesquioxane type on the polyurethane pyrolysis paths. FTIR study of volatile products of thermal decomposition showed the presence of characteristic bands originated from carbonyl, amine, ether, methylene, and unsaturated hydrocarbon linkages. GC/MS investigation confirmed the existence of compounds identified by the IR method. The application of both thermoanalytical methods made it possible to postulate the thermal decomposition routes of PU/POSS hybrids and to point out the main factors responsible for changes in the thermal stability.

Demonstration of Physicochemical and Functional Similarity of the Biosimilar BAT1806/BIIB800 to Reference Tocilizumab.

Tocilizumab is an immunoglobulin G1 monoclonal antibody targeting the interleukin-6 receptor (IL-6R). BAT1806/BIIB800 (tocilizumab-bavi) has been developed as a biosimilar to the reference product tocilizumab (TCZ). The objective of this study was to demonstrate physicochemical and functional similarity between BAT1806/BIIB800 and TCZ in a comprehensive comparability exercise. A comprehensive panel of over 20 methods was used to generate datasets comparing critical and non-critical product quality attributes for 10 BAT1806/BIIB800 lots and 44 TCZ lots (16 sourced from China, 16 from the EU, and 12 from the US). Primary structure, higher-order structure, and physicochemical properties were assessed using liquid chromatography, mass spectrometry, various spectroscopy techniques/methods, capillary electrophoresis, and thermoanalytical techniques. Fragment antigen-binding (Fab)- and fragment crystallizable (Fc)-mediated biological properties were assessed using cell-based assays, immunoassays, flow cytometry, and kinetic binding assays. BAT1806/BIIB800 and TCZ (irrespective of source) were shown to be similar in terms of structural and functional properties. No differences were observed in terms of the most critical quality attributes, that is, soluble-IL-6R binding and inhibition of IL-6-mediated cell proliferation. BAT1806/BIIB800 and TCZ demonstrated similarity in terms of Fab- and Fc-mediated binding and biological activity. Minor differences were observed in glycosylation (afucosylation and sialylation), glycation, aggregation, and charge variants, which were demonstrated to be not clinically relevant. BAT1806/BIIB800 and TCZ were highly similar for all critical quality attributes. Where differences were observed in less critical quality attributes, additional analytical assessments and clinical study results determined these to be not clinically meaningful.

Host-Guest Interaction Study of Olmesartan Medoxomil with β-Cyclodextrin Derivatives.

Olmesartan medoxomil (OLM) is a selective angiotensin II receptor antagonist used in the treatment of hypertension. Its therapeutic potential is limited by its poor water solubility, leading to poor bioavailability. Encapsulation of the drug substance by two methylated cyclodextrins, namely randomly methylated β-cyclodextrin (RM-β-CD) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD), was carried out to overcome the limitation related to OLM solubility, which, in turn, is expected to result in an improved biopharmaceutical profile. Supramolecular entities were evaluated by means of thermoanalytical techniques (TG-thermogravimetry; DTG-derivative thermogravimetry), spectroscopic methods including powder X-ray diffractometry (PXRD), universal-attenuated total reflectance Fourier-transform infrared (UATR-FTIR) and UV spectroscopy, saturation solubility studies, and by a theoretical approach using molecular modeling. The phase solubility method reveals an AL-type diagram for both inclusion complexes, indicating a stoichiometry ratio of 1:1. The values of the apparent stability constant indicate the higher stability of the host-guest system OLM/RM-β-CD. The physicochemical properties of the binary systems are different from those of the parent compounds, emphasizing the formation of inclusion complexes between the drug and CDs when the kneading method was used. The molecular encapsulation of OLM in RM-β-CD led to an increase in drug solubility, thus the supramolecular adduct can be the subject of further research to design a new pharmaceutical formulation containing OLM, with improved bioavailability.

To what extent are wastewater treatment systems a gateway for microplastic particles in the aquatic and terrestrial environments?

Sewage treatment plants are designed to handle wastes that include several types of pollutants, including microplastics (MPs), which are synthetic polymer materials fragmented to sizes < 5 mm. Investigating the abundance and removal efficiency rates of MPs in wastewater treatment plants is important because the water body to which plant effluents are discharged may be adversely affected by the released MPs. Therefore, the abundance, characteristics, and removal of MPs at two sewage treatment plants located on the southwest coast of Norway are studied. Twenty-four samples were collected across two sampling sessions by using an ad hoc-designed plastic-free water sampling device, which was improved by applying a cascade of certified stainless-steel sieves. A combined sequence of enzymatic and strong oxidative incubations was performed for sample preparation. The obtained samples were chemically characterized and quantified using thermoanalytical techniques. The overall amounts of polymers in the inlet wastewater and outlet water were 366-616 μg/L and 34-57 μg/L, respectively, indicating an approximate MPs removal efficiency of 78%-85%. Polyethylene (≈ 36%-68%), polypropylene (≈ 7%-48%), polystyrene (≈ 5%-6%), polyvinyl chloride (≈ 15%-26%), polyamide (≈ 2%), polymethacrylate (≈ 3%-4%), polycarbonate (≈ 2%), and polyethylene terephthalate (≈ 9%-32%) were detected in the investigated samples. In biosolids, the overall quantity of MPs was 3.8-5.5 mg/g dry weight across the two investigated sewage treatment plants. Polyethylene (≈ 24%-44%), followed by polyvinyl chloride (PVC) (≈ 11%-16%), and polyamide (≈ 2%-22%) were the most commonly recurring polymer types. The outcomes of this study indicate that MPs are removed efficiently from wastewaters. However, large amounts of MPs accumulate in biosolids. Therefore, sludge dumping management procedures need to be improved to lower the amount of MPs released into the environment through effluents and biosolids.

PROBLEMS IN THERMAL ANALYSIS OF EXPLOSIVES, WITH PARTICULAR EMPHASIS ON MULTI-COMPONENT EXPLOSIVE COMPOSITIONS

Thermoanalytical techniques, including differential scanning calorimetry and thermo-gravimetry, allow to test the properties of materials using small amounts. They enable obtaining a lot of reliable information about samples of explosives in a relatively short time, while maintaining operator and surroundings safety. The course of measurements and their results depend on many factors, and potential errors can arise at various stages, from taking samples for tests until conclusions are drawn. Appropriate selection of test parameters as well as proper analysis and interpretation of results pose a special challenge for the researcher.Keywords:

Characterization techniques for carbon-based adsorbents and carbon composites

Abstract Adsorption processes are crucial in various applications, especially water and wastewater treatment. The research is focused on improving and developing adsorbent materials. An in-depth evaluation of a recently suggested adsorbent is essential to determine its characteristics, confirm its suitability, and understand its effectiveness in the intended process. Various approaches can be engaged to collect multiple physico-chemical data, with the selection of the methodology contingent on the substance under investigation and the instruments at hand. The accessible procedures include, FTIR, Raman, XPS, EDX, XRD, SEM/FESEM, TEM, AFM, VSM, DLS, and thermoanalytical techniques (TGA, DSC). These methods aid in identifying, locating, and quantifying chemical components. They also enable the analysis of the structure, topography, morphology, magnetic properties, and size, as well as other physical characteristics of materials. This information is valuable for assessing the manufacturing and modification of adsorbent materials and studying the adsorption process by examining the interactions between the adsorbent and the adsorbate. This work aims to offer an inclusive resource for investigators exploring adsorbent resources. It attempts to help them choose the most suitable characterization methods according to their specific needs.

Thermoanalytical techniques applied to the solid-state characterization of atorvastatin calcium trihydrate form I

Atorvastatin calcium trihydrate (ACT) is a synthetic lipid-lowering agent whose thermal character remains largely unknown or else mischaracterized due to being called both “atorvastatin” and “atorvastatin form I” indiscriminately in the literature. Developing stable drugs, however, requires ensuring and thus understanding the reliable thermal behavior of trihydrate drugs, for pharmaceutical manufacturing can involve temperatures that might cause phase transition and/or the dehydration of the drugs, with implications for its physical characteristics, its chemical characteristics, and/or the pharmaceutical product's bioactivity. Against that background, in our study we investigated both a solid-state and thermal characterization of ACT via powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hot-stage microscopy (HSM), and ex situ variable temperature PXRD techniques, all as integral parts of drug development. DSC and TGA curves clarified ACT's thermal stability and dehydration, and the ACT sample was identified as Form I of the trihydrate, which remains stable until approximately 40 °C. DSC showed no significant changes during melting with different heating rates, while the TGA curve revealed the stepwise loss of water molecules following heating. Ex situ PXRD suggested no abrupt changes to the trihydrate's crystal lattice during the dehydration of the first two moles of water molecules. Moreover, HSM clearly showed a unique water loss event never before visualized. Last, HSM confirmed the drug's crystallinity, its crystal shape, and the presence of an isotropic liquid after continuous heating, which remained until cooling to room temperature.

Analysis of the methodology described in the thermoanalytical characterization involving aceclofenac compounds and their derivatives: what does the literature say?

The thermoanalytical characterization of aceclofenac compounds and their derivatives is essential for understanding their physical and chemical properties. Thermoanalytical techniques offer critical insights into these compounds' thermal behavior, stability, and decomposition patterns, providing vital information for their formulation, processing, and storage. Aceclofenac, a diclofenac derivative, is a widely used nonsteroidal anti-inflammatory drug (NSAID) for treating inflammatory diseases. This physicochemical characterization is pivotal for assessing their stability, solubility, and bioavailability, involving various analytical techniques like melting point determination, decomposition temperature assessment, and heat capacity analysis. Thermoanalytical methods like thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) are frequently employed in pharmaceutical compound characterization, offering insights into thermal stability, decomposition kinetics, and molecular structure. This review summarizes recent literature on thermoanalytical methodologies characterizing Aceclofenac and its derivatives. A bibliographic review was conducted using the SciFinder web platform, resulting in the selection of ten relevant articles published between 2016 and 2023. The analysis reveals that thermal analysis is crucial for studying pharmaceuticals, providing insights into various physicochemical properties. Despite the importance of experimental methodologies in scientific publications, some studies lack adequate pre-experimental information, hindering reproducibility. In this review, it was observed that out of eight studies, twelve thermoanalytical techniques were employed for aceclofenac characterization, with DSC being the most used method. However, one author omitted crucial information about experimental procedures, highlighting the need for transparent reporting in scientific research.

Recognition and detection technology for microplastic, its source and health effects.

Microplastic (MP) is ubiquitous in the environment which appeared as an immense intimidation to human and animal health. The plastic fragments significantly polluted the ocean, fresh water, food chain, and other food items. Inadequate maintenance, less knowledge of adverse influence along with inappropriate usage in addition throwing away of plastics items revolves present planet in to plastics planet. The present study aims to focus on the recognition and advance detection technologies for MPs and the adverse effects of micro- and nanoplastics on human health. MPs have rigorous adverse effect on human health that leads to condensed growth rates, lessened reproductive capability, ulcer, scrape, and oxidative nervous anxiety, in addition, also disturb circulatory and respiratory mechanism. The detection of MP particles has also placed emphasis on identification technologies such as scanning electron microscopy, Raman spectroscopy, optical detection, Fourier transform infrared spectroscopy, thermo-analytical techniques, flow cytometry, holography, and hyperspectral imaging. It suggests that further research should be explored to understand the source, distribution, and health impacts and evaluate numerous detection methodologies for the MPs along with purification techniques.

Development and validation of an analytical pyrolysis method for detection of airborne polystyrene nanoparticles

Microplastic is ubiquitous in the environment. Recently it was discovered that microplastic (MP, 1 μm−5 mm) contamination is present in the atmosphere where it can be transported over long distances and introduced to remote pristine environments. Sources, concentration levels, and transportation pathways of MP are still associated with large uncertainties. The abundance of atmospheric MP increases with decreasing particle size, suggesting that nanoplastics (NP, <1μm) could be of considerable atmospheric relevance. Only few analytical methods are available for detection of nanosized plastic particles. Thermoanalytical techniques are independent of particle size and are thus a powerful tool for MP and NP analysis. Here we develop a method for analysis of polystyrene on the nanogram scale using pyrolysis gas chromatography coupled to mass spectrometry. Pyrolysis was performed using a slow temperature ramp, and analytes were cryofocused prior to injection. The mass spectrometer was operated in selected ion monitoring (SIM) mode. A lower limit of detection of 1±1 ng and a lower limit of quantification of 2±2 ng were obtained (for the trimer peak). The method was validated with urban ▪ matrices of low (7 μg per sample) and high (53 μg per sample) aerosol mass loadings. The method performs well for low ▪ loadings, whereas high ▪ loadings seem to cause a matrix effect reducing the signal of polystyrene. This effect can be minimized by introducing a thermal desorption step prior to pyrolysis. The study provides a novel analysis method for qualitative and semi-quantitative analysis of PS on the nanogram scale in an aerosol matrix. Application of the method can be used to obtain concentration levels of polystyrene in atmospheric MP and NP. This is important in order to improve the understanding of the sources and sinks of MP and NP in the environment and thereby identify routes of exposure and uptake of this emerging contaminant.

Schiff Bases, Syntheses, Characterisation and their Application to Heavy Metal Removal: A Review

Schiff bases are compounds resulting from the condensation reaction between an aldehyde or ketone with primary amines. The confirmation of the formation of these compounds involves the use of characterisation techniques which encompasses spectroscopic and thermoanalytical techniques. Recently, Schiff bases have garnered attention because of their wide applications which range from industrial uses to use in remediation of metal ions. Their use in extraction of heavy metal is of particular interest due to rising levels of metal pollution globally. The ability of Schiff bases to form coordination complexes with metal ions makes them suitable for these purposes. This review article outlines the synthesis, characterisation and application of Schiff bases to metal extraction.

THE POWDER OF Co64Nb30B6 OBTAINED BY MECHANICAL ALLOYING

This work aims to synthesize the alloy Co64Nb30B6 through mechanical alloying using a planetary ball mill. A disc rotation per minute and a ball/powder weight ratio of 300 rpm and 10:1 were used, with a milled time of 10 h, respectively. The characterization of the Co64Nb30B6 alloy was performed by X-ray diffraction (XRD), examined by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), thermoanalytical techniques (TGA/DTA), vibrating sample magnetometer (VSM) and confirmed by Braunauer, Emmet e Teller (BET) method type IV isotherms with a hysteresis loop for mesoporous materials. The results indicated that the evolution of the amorphous phase in the Co64Nb30B6 composition through the mechanical alloying process exhibited good soft magnetic properties with the addition of the metalloid element B and its excellent unique ferromagnetic properties. Through thermoanalytical analysis (TGA/DTA), it was shown that at higher temperatures, Co and Nb ions are oxidized by the environment and, therefore, the mass can be slightly increased to 14.9% and a probable contribution of boron in evolution stability thermal and magnetic in the amorphous phase, respectively. This suggests that the newly developed high-performance amorphous alloy Co64Nb30B6 has great application potential.

Investigating the thermal behavior of acyclovir

Viruses are a significant health, economic and social issue. Acyclovir (ACV) is an antiviral agent analogous to the guanine nitrogenous base that acts by interrupting the multiplication of DNA of virus in infected cells. The thermal decomposition mechanism of ACV was evaluated by thermoanalytical techniques Thermogravimetry/derivative thermogravimetry (TG/DTG), differential thermal analysis (DTA), evolved gas analysis by thermogravimetry coupled to vibrational infrared spectrometry in gas phase (TG-FTIR), differential scanning calorimetry (DSC), hot stage microscopy (HSM) and mass spectrometry (MS). TG/DTG and DTA curves were performed under N2 and air atmospheres. Under N2, four stages of mass loss were observed from the TG curve between 523-1273 K, while under air decomposition occurred in a similar way, however, the additional burning of carbonaceous material was found in air. DSC curves were obtained in heat-cool-heat mode, from 233 to 543 K, under N2 atmosphere and presented two endothermic peaks related to water loss and phase transition followed by exothermic crystallization of a new form, followed by melting associated with decomposition in agreement with HSM images. Powder X-ray diffraction (PXRD) profiles confirmed the phase transitions. From the TG-FTIR characterization, it was suggested that decomposition undergoes by release of water, 1,3-dioxolane, isocyanic acid, carbon dioxide, carbon monoxide, and ammonia. MS spectrum of the residue collected at 543 K revealed the presence of guanine free base as decomposition product in agreement with the release of dioxolane ring in gas phase.

Characterization and Reverse Engineering of Pharmaceuticals: Role of Thermoanalytical Techniques

During pharmaceutical or biopharmaceutical drug product development, one of the most important steps to be followed is characterization and reverse engineering of the drug product. Out of so many characterization tools and orthogonal reverse engineering techniques, thermoanalytical methods are the most useful techniques. Different thermoanalytical techniques are used to identify, quantify and understand the interaction between different polymorphic forms of drug substances and excipients. These techniques are also used to monitor the physical form (amorphous or crystalline) of the drug substance in drug product throughout its manufacturing processes and helps in identifying, omitting or modifying the steps or processes responsible for change in physical or polymorphic form of the drug substance in the finished drug product. Thermoanalytical techniques are not only useful for characterization of small molecules but also extensively applied in analysis of biological samples and nano-formulations. In current scenario, pharmaceutical development specifically during generic drug development the most useful step is the reverse engineering. When reverse engineering of drug product is concerned, thermoanalytical techniques are the best tools to be used to prove the similarity of physico-chemical properties or same state of matter or arrangement of matter between test and reference products. However, in earlier days these techniques were not used as frequently as the other techniques like spectroscopy and chromatography. Various reasons for limited use of thermoanalytical techniques were unavailability of software or compatible hardware, manual sampling process and a tedious process of manual calculation which consumes lots of time. Now a day, due to advancement of technology, automation, use of robotics, and better understanding, and the thermal analysis not only become a powerful tool but also increase the throughput. The present review focuses on some of the most commonly used Thermoanalytical techniques e.g. Differential Scanning Calorimeter (DSC), Thermogravimetric Analysis (TGA), Solution Calorimeter (SC), Thermo Mechanical Analysis (TMA) and Isothermal Titration Calorimeter (ITC) for characterization and reverse engineering of different dosage forms like solid oral dosage forms, injectable formulation, inhalation formulation, ophthalmic formulation, and biosimilar formulation products such as peptides and proteins using specific case studies.

AlCl3-NaCl-ZnCl2 Secondary Electrolyte in Next-Generation ZEBRA (Na-ZnCl2) Battery

Increasing demand to store intermittent renewable electricity from, e.g., photovoltaic and wind energy, has led to much research and development in large-scale stationary energy storage, for example, ZEBRA batteries (Na-NiCl2 solid electrolyte batteries). Replacing Ni with abundant and low-cost Zn makes the ZEBRA battery more cost-effective. However, few studies were performed on this next-generation ZEBRA (Na-ZnCl2) battery system, particularly on its AlCl3-NaCl-ZnCl2 secondary electrolyte. Its properties such as phase diagrams and vapor pressures are vital for the cell design and optimization. In our previous work, a simulation-assisted method for molten salt electrolyte selection has shown its successful application in development of molten salt batteries. The same method is used here to in-depth study the AlCl3-NaCl-ZnCl2 salt electrolyte in terms of its phase diagrams and vapor pressures via FactSageTM and thermo-analytical techniques (Differential Scanning Calorimetry (DSC) and OptiMeltTM), and their effects on battery performance such as operation safety and charging/discharging reaction mechanism. The DSC and OptiMelt results show that the experimental data such as melting temperatures and phase changes agree well with the simulated phase diagrams. Moreover, the FactSageTM simulation shows that the salt vapor pressure increases significantly with increasing temperature and molar fraction of AlCl3. The obtained phase diagrams and vapor pressures will be used in the secondary electrolyte selection, cell design and battery operation.

Thermal dehydration of D-glucose monohydrate in solid and liquid states.

The physico-geometrical reaction pathway and kinetics of the thermal dehydration of D-glucose monohydrate (DG-MH) dramatically alter by the melting of the reactant midway through the reaction. By controlling the reaction conditions, the thermal dehydration of DG-MH was systematically traced by thermoanalytical techniques in three different reaction modes: (1) solid-state reaction, (2) switching from a solid- to liquid-state reaction, and (3) liquid-state reaction. Solid-state thermal dehydration occurred under isothermal conditions and linear nonisothermal conditions at a small heating rate (β ≤ 1 K min-1) in a stream of dry N2. The kinetic behavior comprised the presence of an induction period and a sigmoidal mass loss process characterized by a derivative mass loss curve with a symmetrical shape under isothermal conditions, resembling the autocatalytic reaction in homogeneous kinetic processes. When DG-MH was heated at a larger β (≥2 K min-1), the melting of DG-MH occurred midway through the thermal dehydration process, by which a core-shell structure of molten DG-MH and surface product layer of crystalline anhydride was produced. Subsequently, thermal dehydration proceeded as a complex multistep process. Furthermore, the thermal dehydration initiated at approximately the melting point of DG-MH upon the application of a certain water vapor pressure to the reaction atmosphere, and proceeded in the liquid-state, exhibiting a smooth mass loss process to form crystalline anhydride. The reaction pathway and kinetics of the thermal dehydration of DG-MH and the corresponding changes with the sample and reaction conditions are discussed on the basis of the detailed kinetic analysis.

Ammonium affects the wet chemical network of HCN: feedback between prebiotic chemistry and materials science.

Prebiotic chemistry one-pot reactions, such as HCN-derived polymerizations, have been used as stimulating starting points for the generation of new multifunctional materials due to the simplicity of the processes, use of water as solvent, and moderate thermal conditions. Slight experimental variations in this special kind of polymerization tune the final properties of the products. Thus, herein, the influence of NH4Cl on the polymerization kinetics of cyanide under hydrothermal conditions and on the macrostructures and properties of this complex system is explored. The kinetics of the process is consistent with an autocatalytic model, but important variations in the polymerization reaction are observed according to a simple empirical model based on a Hill equation. The differences in the kinetic behaviour against NH4Cl were also revealed when the structural, morphological, thermal, electronic and magnetic properties of the synthesized cyanide polymers were compared, and these properties were evaluated by elemental analysis, FTIR, XPS, UV-vis, and ESR spectroscopies, X-ray diffraction, SEM and thermoanalytical techniques. As a result, this hydrothermal prebiotic polymerization is not only pH dependent, as previously thought, but also ammonium subservient. From this result, a hypothetical reaction mechanism was proposed, which involves the active participation of ammonium cations via formamidine and serves as a remarkable point against previous reports. The results discussed here expand the knowledge on HCN wet chemistry, offer an extended view of the relevant parameters during the simulation of hydrothermal scenarios and describe the production of promising paramagnetic and semiconducting materials inspired by prebiotic chemistry.

Digest, stain and bleach: Three steps to achieving rapid microplastic fluorescence analysis in wastewater samples

Efforts associated with common analytical techniques for microplastics including spectroscopic and thermo-analytical techniques are limiting the ability to perform large-scale monitoring of microplastics in the aquatic environment, because the analytical equipment required is costly and the analysis itself time consuming. Thus, there is a need to develop low cost, rapid alternative monitoring approaches. One possible alternative is the use of selective fluorescence staining of microplastic particles directly applied to environmental samples. However, to the best of our knowledge this has not yet been successfully implemented for wastewater samples. In this study, sludge samples are used as surrogates for wastewater alongside six different polymers to develop a combined sample preparation and staining protocol that could selectively stain microplastics without significant interference from the natural constituents of the sludge. Results confirmed that using Fenton's reagent to remove the organic matter before staining the sample with Nile red (NR) and subsequently bleaching it by sodium hypochlorite resulted in the best workflow to selectively stain microplastics and then analyze them in wastewater samples using fluorescence microscopy.

Thermoanalytical techniques for characterizing sintering processes in ferrous powder metallurgy

For powder metallurgy processing, the sintering stage, i.e. the heat treatment of a the powder compact below the melting point of -at least- the major component, is decisive for establishing microstructure and properties. Thorough studying of the chemical and metallurgical processes occurring during sintering is essential for attaining optimal product properties, and sintering has therefore been the focus of investigations for many decades. Thermoanalytical techniques, at best combined with chemical analysis, enable in-situ characterization of the sintering process from many perspectives. When using these techniques in powder metallurgy, it should be considered that the very large specific surface of a powder compact, compared to a solid metallic body, results in much higher reactivity with the surrounding atmosphere. This atmosphere is on the one hand the “external” one, outside the body in the free space of the furnace, and on the other hand the “internal” one within the pore network of the specimen. This paper shows different examples of how critical information about the sintering process can be described by using thermoanalytical techniques combined with mass spectroscopy: e.g. phase transformations and liquid phase formation in the powdered compact, deoxidation and decarburization reactions, and interstitial redistribution in sintered alloy steels prepared through different alloying techniques.