Aqueous Sodium Hydroxide Solution Research Articles

Probing the Closed Association of Oligoquinoline Foldamers by Time-Resolved Fluorescence Anisotropy.

The metal-mediated dimerization of oligoquinoline foldamers terminated at one end with an oligo(phenylenevinylene) and at the other with a carboxylic acid (OPV-QnA, where n = 4, 8, 17, and 33), and the complexation of OPV-Q8A and Q16A was promoted in chloroform by the addition of a concentrated 16 M aqueous sodium hydroxide solution. UV-vis absorption and time-resolved fluorescence anisotropy (TRFA) experiments were conducted to determine, respectively, the concentration and the average rotational time ⟨ϕ⟩ of the mixture of unassociated and associated foldamers across a range of foldamer concentrations spanning 5 orders of magnitude. Plots of ⟨ϕ⟩ as a function of acid group concentration revealed that ⟨ϕ⟩ increased with increasing foldamer concentration only when the foldamer solution in chloroform was vigorously mixed with the 16 M sodium hydroxide aqueous solution. Furthermore, all plots showed that ⟨ϕ⟩ reached a plateau at high foldamer concentration. The increase in ⟨ϕ⟩ reflected the association of foldamers into larger objects through metal ion coordination with the carboxylate anions generated by deprotonation of the carboxylic acid of OPV-QnA with NaOH, while the plateau obtained at high foldamer concentration indicated that these interactions led to the dimerization of the foldamers via a closed association mechanism. Analysis of the ⟨ϕ⟩ trends yielded the equilibrium constants (K) describing the foldamer dimerization, whose value equaled 1.0 (±0.2) × 106 M-1 for the three longer OPV-QnA foldamers, but was about 10 times smaller for the shortest one (n = 4). Association of OPV-Q8A and Q16A yielded a complex with a ⟨ϕ⟩ matching that of OPV-Q24A, and K for this complexation was similar to that for dimerization. These experiments illustrate the robust nature of TRFA as an experimental method to probe the size of rigid, self-assembled foldamers in solution.

Xylometazoline base suitable for use in lipophilic drug products: development of production technology and analytical methods for quality control

The aim: development of the technology for obtaining the base of xylometazoline, suitable for the development of formulations in combination with essential oils. Development and validation of methods of control of related substances and assay of the obtained base of xylometazoline. Study of the stability of the obtained xylometazoline base under long-term and accelerated conditions. Materials and methods: experimental samples of xylometazoline base were obtained from commercially available xylometazoline hydrochloride and aqueous sodium hydroxide solution. The quality control of the obtained substance was carried out in accordance with the requirements of the internal specification. The analysis of raw materials of xylometazoline hydrochloride was carried out in accordance with the monograph of the European Pharmacopoeia on xylometazoline hydrochloride (Ph. Eur. 10.1, 1162 (01/2008)). Results: a technology for obtaining xylometazoline base from xylometazoline hydrochloride by the action of a 2 % solution of a strong base, namely sodium hydroxide, was developed. Developed and validated methods of quality control of the obtained xylometazoline base according to indicators of related substances and assay. The stability of the substance was studied for 1 year; the results of control under accelerated research conditions meet the requirements of the specification, which allows for establishing a shelf life of 2 years. Conclusions: the technology for obtaining xylometazoline base and quality control methods based on the monograph of the European Pharmacopoeia on xylometazoline hydrochloride was developed. The developed technology ensures the proper quality of the substance in accordance with the requirements of the internal specification. Analytical methods "related substances" and "assay" meet the established criteria during validation. The obtained results were later used to develop a medicine based on xylometazoline and eucalyptus oil – Eukazolin, nasal drops

Rapid determination of nine preservatives in tobacco flavor by three phase-hollow fiber-liquid phase microextraction-high performance liquid chromatography

Tobacco flavors are extensively utilized in traditional tobacco products, electronic nicotine, heated tobacco products, and snuff. To inhibit fungal growth arising from high moisture content, preservatives such as benzoic acid (BA), sorbic acid (SA), and parabens are often incorporated into tobacco flavors. Nonetheless, consuming preservatives beyond safety thresholds may pose health risks. Therefore, analytical determination of these preservatives is crucial for both quality assurance and consumer protection. For example, BA and SA can induce adverse reactions in susceptible individuals, including asthma, urticaria, metabolic acidosis, and convulsions. Parabens, because of their endocrine activity, are classified as endocrine-disrupting chemicals. Despite extensive research, the concurrent quantification of trace-level hydrophilic (BA and SA) and hydrophobic (methylparaben, ethylparaben, isopropylparaben, propylparaben, butylparaben, isobutylparaben, and benzylparaben) preservatives in tobacco flavors remains challenging. Traditional liquid phase extraction coupled with high performance liquid chromatography (HPLC) often results in high false positive rates and inadequate sensitivity. In contrast, tandem mass spectrometry offers high sensitivity and specificity; however, its widespread application is limited by laborious sample preparation and significant operational costs. Therefore, it is crucial to establish a fast and sensitive sample pretreatment and analysis method for the nine preservatives in tobacco flavors. In this study, a method for the simultaneous determination of the nine preservatives (SA, BA and seven parabens) in tobacco flavor was established based on three phase-hollow fiber-liquid phase microextraction (3P-HF-LPME) technology combined with HPLC. To obtain the optimal pretreatment conditions, extraction solvent type, sample phase pH, acceptor phase pH, sample phase volume, extraction time, and mass fraction of sodium chloride, were examined. Additionally, the HPLC parameters, including UV detection wavelength and mobile phase composition, were refined. The optimal extraction conditions were as follows: dihexyl ether was used as extraction solvent, 15 mL sample solution (pH 4) was used as sample phase, sodium hydroxide aqueous solution (pH 12) was used as acceptor phase, and the extraction was carried out at 800 r/min for 30 min. Chromatographic separation was accomplished using an Agilent Poroshell 120 EC-C18 column (100 mm×3 mm, 2.7 μm) and a mobile phase comprising methanol, 0.02 mol/L ammonium acetate aqueous solution (containing 0.5% acetic acid), and acetonitrile for gradient elution. Under the optimized conditions, the nine target analytes showed good linear relationships in their respective linear ranges, the correlation coefficients (r) were ≥0.9967, limits of detection (LODs) and quantification (LOQs) were 0.02-0.07 mg/kg and 0.08-0.24 mg/kg, respectively. Under two spiked levels, the enrichment factors (EFs) and extraction recoveries (ERs) of the nine target analytes were 30.6-91.1 and 6.1%-18.2%, respectively. The recoveries of the nine target analytes ranged from 82.2% to 115.7% and the relative standard deviations (RSDs) (n=5) were less than 14.5% at low, medium and high levels. The developed method is straightforward, precise, sensitive, and well-suited for the rapid screening of preservatives in tobacco flavor samples.

Activation of additively manufactured electrodes using methanol and ethanol solutions

AbstractThe use of polymer additive manufacturing to produce electrodes is an increasingly popular area of electrochemical research. However, one downside of additively manufactured electrodes is the frequent need to remove polymer from the electrode surface to reveal a triple‐phase boundary in order for improved electrode performance to be realized. A common way to achieve this, is surface activation via chronoamperometry within an aqueous sodium hydroxide solution. However, it has not been investigated whether the same activation can be carried out effectively in solutions of sodium hydroxide in simple alcohols. Therefore, in this work, we study the effect of performing common chronoamperometric additive manufacturing electrode activation methodologies in methanolic and ethanolic solutions of 0.05 M sodium hydroxide and compare these to activation carried out in standard aqueous solutions at concentrations of both 0.05 M and 0.5 M. We show that the alcoholic solutions are more effective in removing polymer from the additive manufacturing electrode surface, but that this does not lead to any improvement in electrode currents, and furthermore appears to hinder electron transfer kinetics at the additive manufacturing electrode surface, with the latter effect shown to be related to differences in the surface functionality of the exposed carbon black filler particles. As well as being interesting chemical experiments in their own right, these results may well be of interest to electrochemists who intend for their additive manufactured electrodes to be applied in these alcohols or indeed other non‐aqueous solvents.

A Metatitanic Acid Particulate Xerogel: Green Synthesis, Structure Determination, and Detailed Characterization.

The manuscript focuses on an original method of preparation of metatitanic acid when only environmentally safe base substances are used in the synthesis process. The synthesis is based on the reaction of solid titanyl sulfate in an aqueous solution of sodium hydroxide. This method allows for (i) a full preservation of the morphology of the starting titanyl sulfate and (ii) a preparation of metatitanic acid substances with specific parameters. This can be achieved via a precise control of the alkali metal/titanyl sulfate ratio resulting in substances with varying contents of alkali metals or even sulfate anions. The prepared metatitanic acid then also contains very small weakly crystalline particles (2-3 nm) and forms pseudomorphic aggregates whose shape and dimensions correspond to those of the starting titanyl sulfate. These aggregates exhibit regular nanoporosity with a high surface area of up to 500 m2·g-1, have no tendency to form colloids, and are mechanically highly resistant even by high-energy ultrasound. The characterization of the resulting products is done via their chemical composition and methods of structural analysis, as well as by electron microscopy and local analysis. The mechanism of product formation is discussed based on the structure of the precursor, including the so far unknown structure of metatitanic acid.

Synthesis, characterization and performance of quaternized cellulose based flocculant derived from office paper waste for dye removal

Abstract The quaternized cellulose derivatives (QCs) were synthesized by reacting extracted cellulose from office paper waste with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) in an aqueous solution of sodium hydroxide (NaOH) – urea. The characterization results by using Fourier-Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the office paper waste properties changed after chemical treatment and the extract product was confirmed cellulose. In addition, the FT-IR and SEM results confirmed the successful introduction of cationic quaternary ammonium groups into the main chain of cellulose. Meanwhile, the XRD results revealed that the crystalline structure was destroyed during etherification reaction. By using synthetic Congo red dye, the flocculation performance of the QCs was evaluated via standard jar test method at different QC dosages, initial Congo red dye concentration and pH values. It was found that the QC10 exhibited a more effective flocculation capability as compared to other synthesized QCs for over a wide pH value. The QC10 performed the best at pH 7, 100 mg/L of Congo red dye concentration and 50 mg/L of QC dosage, with percentage removal of 89.09 %. These findings demonstrated the potential application of QC in dye removal.

Potential of Bioactive Protein and Protein Hydrolysate from Apis mellifera Larvae as Cosmeceutical Active Ingredients for Anti-Skin Aging.

This study aimed to extract bioactive proteins and protein hydrolysates from Apis mellifera larvae and assess their potential application in cosmetics as well as their irritation properties. The larvae were defatted and extracted using various mediums, including DI water, along with 0.5 M aqueous solutions of sodium hydroxide, ascorbic acid, citric acid, and hydrochloric acid. Subsequently, the crude proteins were hydrolyzed using the Alcalase® enzyme. All extracts underwent testing for antioxidant activities via the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and Griess assays. Anti-aging properties were evaluated in terms of anti-collagenase and anti-hyaluronidase effects. Irritation potential was assessed using the hen's egg chorioallantoic membrane (HET-CAM) test. The results revealed that the sodium hydroxide extraction showed promising outcomes in terms of yield, protein content, and effectiveness in inhibiting hyaluronidase, with the highest inhibition at 78.1 ± 1.5%, comparable to that of oleanolic acid. Conversely, crude protein extracted with ascorbic acid and its hydrolysate showed notable antioxidant and collagenase-inhibitory activities. Remarkably, their anti-collagenase effects were comparable to those of ascorbic acid and lysine. Additionally, it demonstrated safety upon testing with the CAM. In conclusion, the findings provided valuable insights into the utilization of A. mellifera larval proteins as active ingredients with a wide range of cosmeceutical applications, particularly due to their antioxidant, anti-aging, and low irritation properties, which hold significant promise for anti-skin wrinkles.

Changes in crystallinity of sago palm (Metroxylon sago spp.) waste during cellulose extraction

Changes in crystallinity of sago palm (Metroxylon sago spp.) waste during cellulose extraction

Sodium Cerium Phosphate, (Na,Ce)2Ce(PO4)2 ⋅ xH2O, with Mixed Cerium Oxidation States

AbstractA previously unknown double ceric sodium phosphate hydrate Na1.97Ce1.03(PO4)2 ⋅ xH2O containing both ceric and cerous cations was obtained by the hydrothermal treatment of amorphous ceric phosphate mixed with a sodium hydroxide aqueous solution. The presence of Ce3+ in the structure was proved by HERFD‐XANES and ESR spectroscopy. Iterative transformation factor analysis of HERFD‐XANES data allowed estimating the content of Ce3+ as 10 % of the total cerium. Water content of x=0.55 has been determined by thermogravimetric analysis combined with mass‐spectrometry data. The structure of the compound was solved from powder X‐ray diffraction data (S.G. P21/c a=6.9441(2) Å, b=11.6805(3) Å, c=9.3434(3) Å, β=111.6827(18)°). The new ceric sodium phosphate hydrate has a tunnel structure, where Ce3+ cations most likely partially occupy Na+ positions. The crystal structure of the novel compound has no direct analogues among the crystal structures of double tetravalent metal phosphates.

Oligomerization of dibrominated aminophenol on the basis of the chemical and HRP-catalyzed oxidative processes: Characterization and photoluminescence properties

Preparation of oligo (aminophenols) was carried out by chemical oxidative and enzymatic oligomerization of 4-amino-2,6-dibromophenol (ADBP). The former method required hydrogen peroxide as catalyst in an aqueous sodium hydroxide solution and the latter method was catalyzed by an enzyme, horseradish peroxidase, in 1,4-dioxane resulting in the formation of (ADBP)-ox and (ADBP)-enz, respectively. For the structural confirmation for both of the synthesized oligomers were fulfilled using FT-IR, UV–vis and 1H NMR and 13C NMR instruments. The chemical oxidation with H2O2 induced monodisperse particles in the sub-micron size. The thermal treatment of the oligomers at 1000 οC showed that the chemical oxidation resulted in (ADBP)-ox with higher residue% compared to enzymatic oxidation. Neutral ADBP underwent facile oxidation, leading to the formation of its corresponding oligomers, which were composed of head-to-tail or ortho-coupled constitutional moieties with lower optical and electrochemical band gaps than those of ADBP using two oligomerization routes. By analyzing the solvent effect on the absorption, lower optical band gaps of the synthesized oligomers were obtained in some selected solvents, pointing out them as semi-conductive material for the production of optoelectronic and electronic materials. By tuning the excitation wavelength, the fluorescence intensity of both of the oligomers was changed. DMF solution of (ADBP)-ox and (ADBP)-enz had a quantum yield of 17.6 % and 1.2 % for green and orange photoluminescence emission, respectively, with excellent photostability.

Internal circulation in carrier phase slugs and its influence on the local hydrodynamics in reactive liquid–liquid segmented flow: Visualisation and PIV studies

Local velocity profiles and fluid circulation in liquid–liquid segmented flow significantly influence interphase mass transfer and associated chemical reactions in reduced dimensions. The present study considers a mass transfer-controlled pseudo first order reaction between iodine dissolved in toluene plugs (dispersed phase) and aqueous sodium hydroxide solution (carrier phase). The circulation patterns in the aqueous slugs observed during PIV experiments are correlated with the overall reaction rate. The extent of reaction is identified by decolourisation of the toluene plugs which is a result of iodine depletion. The experiments reveal that an increase in dispersed phase flow rate increases the circulation rate and local velocity within the carrier phase slugs. This is accompanied by propagation of reactant depletion zone from top to bottom within the organic plug and flattening of plug bottom. Nevertheless, the circulation remains axisymmetric with the stagnation region unchanged at r0 ∼ 0.74R.

THE EFFECT OF PLASMA SURFACE TREATMENT ON THE STRUCTURE OF THE LEAD SULFIDE FILM

In this work, the effect of the substrate surface on the formation of structured lead sulfide films is studied. For this purpose, the surface of single-crystalline silicon (100) was subjected to plasma treatment in a glow discharge in an argon atmosphere, at a working pressure of 1 Pa and a potential difference across the electrodes of 2 kV. Lead sulfide films were obtained on treated and untreated single-crystalline silicon surfaces by chemical deposition from an aqueous solution of lead nitrate, thiourea and sodium hydroxide at a temperature of 70°C for 30 minutes. The surface morphology, elemental composition, and crystal structure were studied by scanning electron microscopy, energy dispersive analysis, and X-ray diffraction, respectively. As a result, the films deposited on pretreated substrates have a distinctly different surface structure compared to films deposited on untreated substrates. Under the same synthesis conditions, the growth of crystals on the treated surface occurred predominantly along certain lines and were grouped into individual particles, while on the untreated surface a continuous film was formed. Thus, through plasma treatment, crystal growth can be controlled to create nanostructures.

Dissolution dynamics of poly(4-hydroxystyrene) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions investigated by quartz crystal microbalance (QCM) method

Abstract The molecular size of alkaline cation has been reported to affect the dissolution of resist film in alkaline aqueous solution. However, the details are still unclear. In this study, the dissolution dynamics of poly(4-hydroxystyrene) (PHS) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions was investigated to clarify the effects of small alkaline cations on the dissolution dynamics of typical backbone polymer for chemically amplified resists by a quartz crystal microbalance (QCM) method. The temporal changes in the frequency and impedance of QCM substrates during development were measured. The maximum impedance reachable during development significantly exceeded that of the developer saturated with PHS unlike the case of tetramethylammonium and tetraethylammonium cations. This means that the PHS matrix near surface was swollen by decreasing the size of alkaline cation. By either increasing or decreasing the size of alkaline cation from tetramethylammonium and tetraethylammonium cations, the transient swelling layer became thick.

Surface Modification of Montmorillonite Clay Towards the Fabrication of Nanocomposites for Engineering Applications

Montmorillonite (MMT) is a layered clay mineral composed of silica and alumina sheets with a layer thickness of about 1 nm qualifies it as a two-dimensional nanomaterial. MMT is found in natural clay ores in the Murunkan, Kirinda, and Okanda areas in Sri Lanka. Nanocomposites with enhanced physical and mechanical properties can be prepared by dispersing MMT in a polymer matrix. However, the hydrophilic nature of MMT hinders the incorporation of MMT into hydrophobic polymer matrices. Hence, a suitable surface modification is required to make MMT compatible with polymers. The present study was based on the preparation and analysis of organically modified calcium Montmorillonite (Ca-MMT)-polypropylene nanocomposites as a green technology initiative. Homo-ionic Ca-MMT was prepared by treating commercial MMT-K10 with a CaCl2 solution. The predominant exchangeable divalent cations present in MMT-K10 and Ca-MMT were determined using AAS. The cation exchange capacity of Ca-MMT was about two times greater than that of MMT-K10. Furthermore, XRD analysis showed a slight increase in d- spacing of Ca-MMT compared to MMT-K10. A novel ligand, triethylene glycol dodecyl methyl ether was synthesized by treating triethylene glycol monomethyl ether (TGME) with 50% w/w aqueous solution of sodium hydroxide followed by 1-bromododecane with the molar ratio of TGME:NaOH:1-bromododecane in 1:2:2. The crude product was purified by column chromatography and characterized by FTIR and GCMS analysis. Hydrophilic Ca-MMT was surface modified with the organic ligand presumably via the coordination of triethylene glycol moiety with Ca2+ cations at the outer edge of the MMT particles. The long aliphatic chains in the periphery of the modified MMT particle make it more organophilic. Modified Ca-MMT was characterized by XRD, TGA, and FTIR analysis. The XRD revealed a slight increase in the d-spacing related to the 001 plane of modified Ca-MMT compared to unmodified clay. The effect of modified Ca-MMT loadings (0.5%, 1%, and 1.5%) on the mechanical properties of the nanocomposite was studied. The results implied an enhancement of the mechanical properties in terms of impact resistance, hardness, and flexural properties in the nanocomposite compared to the virgin polymer. The fabricated nanocomposite is a promising engineering material that may have applications in automotive, construction, and packaging products.
 
 Keywords: Montmorillonite, Polypropylene, Nanocomposite, TGME, Compatibility

Preparation of nano zinc borate and investigation of flame-retardancy of ternary combination nano zinc borate/red phosphorus/expandable graphite on HDPE

Nano zinc borates were successfully synthesised from aqueous solutions of zinc sulfate, boric acid, and sodium hydroxide via the precipitation method. The effects of pH, temperature, and surfactants on the structure and morphologies of nano zinc borates were investigated. The nano zinc borates obtained at the pH of 7 to 8 were well-crystallised monophase Zn[B3O4(OH)3]. The morphologies of nano zinc borates were highly impacted by the reaction temperature and the surfactants. At the range of temperatures from 70 to 80oC, the nano zinc borates were nanoplates of 40-50 nm in thickness. The nano zinc borates grew out of the surface to form nanorods at 90oC and nanowhiskers at 100oC. The nano zinc borates modified with surfactants tended to form larger and thinner plate-like nanoparticles. In the presence of Tween 80, petal-like nano zinc borates were achieved. The petal-like nano zinc borates showed good flame retardant synergistic effects with red phosphorus and expandable graphite on high-density polyethylene matrix. Additionally, the nano zinc borates nanopetals significantly improved the mechanical properties of red phosphorus/expandable graphite/high-density polyethylene composites.

POROUS FLY ASH-BASED GEOPOLYMER USABLE AS AN UNCONVENTIONAL CONSTRUCTION MATERIAL

Geopolymer foam with thermal insulation properties was made by foaming the alumino-silicate mixture composed of fly ash and clay brick waste activated with alkaline activator (water glass and sodium hydroxide in aqueous solution). Other mixture components were expanded perlite as siliceous additive, usual fine aggregate (quartz sand), and less frequently used surfactant (olive oil). The main characteristics of the geopolymer foam were: low density, low thermal conductivity, and relatively high compressive strength. The residual materials contributed to low costs and the complete replacement of ordinary cement led to the significant reduction of CO2 emissions.

3D printing of polyvinyl alcohol hydrogels enabled by aqueous two-phase system.

The synthesis of PVA hydrogels (PVA-Hy) requires a highly basic environment (e.g., an aqueous solution of sodium hydroxide, NaOH, 14% w/w, 4.2 M), but the rapid crosslinking of PVA due to high pH makes it challenging to perform layer-by-layer three-dimensional (3D) printing of PVA-Hy. This work demonstrated 3D printing of PVA-Hy in moderate alkaline conditions (e.g., NaOH, 1% w/w, 0.3 M) assisted by aqueous two-phase system (ATPS). Salting out of PVA to form ATPS allowed temporal shape retention of a 3D-printed PVA structure while it was physically crosslinked in moderate alkaline conditions. Crucially, the layer-to-layer adhesion of PVA was facilitated by delayed crosslinking of PVA that required additional reaction time and overlapping between the layers. To verify this principle, we studied the feasibility of direct ink write (DIW) 3D printing of PVA inks (5-25% w/w, μ = 0.1-20 Pa s, and MW = 22 000 and 74 800) in aqueous embedding media offering three distinct chemical environments: (1) salts for salting out (e.g., Na2SO4), (2) alkali hydroxides for physical crosslinking (e.g., NaOH), and (3) a mixture of salt and alkali hydroxide. Our study suggested the feasibility of 3D-printed PVA-Hy using the mixture of salt and alkali hydroxide, demonstrating a unique concept of embedded 3D printing enabled by ATPS for temporary stabilization of the printed structures to facilitate 3D fabrication.

Simultaneous determination of six nitroaromatic compounds and three anions in environmental matrices using a liquid chromatography-ion chromatography coupled system

Nitroaromatic compounds are used extensively in various fields such as dyes, pesticides, spices, pharmaceuticals, and explosives. However, the residual raw materials of these compounds accumulate in the environment and pose serious risks to human health. Chronic exposure to low concentrations of nitroaromatic compounds can cause anemia, cancer, and organ damage. Currently, Fenton oxidation and natural bioremediation are the processes most often used to eliminate nitroaromatic compounds from environmental water and soil. According to previous research, the presence of inorganic anions such as chloride, nitrite, and nitrate ions in the environmental matrix exerts an inhibitory effect on the biodegradation of nitroaromatic compounds. Furthermore, high nitrate levels in drinking water can lead to the production of nitrosamine carcinogens, which affect ecological safety and human health, in water bodies. Thus, the simultaneous determination of nitroaromatic compounds and chloride, nitrite, and nitrate ions in environmental soil and water matrices is critical for selecting appropriate nitroaromatic compound degradation methods and monitoring surface water quality. Traditional detection methods require two sample pretreatment steps and two instrumental analytical techniques to determine nitroaromatic compounds and inorganic anions in environmental matrices; moreover, these methods are time consuming, labor intensive, and error prone. Therefore, in this study, a method that combines high performance liquid chromatography (HPLC) and ion chromatography (IC) was developed to simultaneously detect nitroaromatic compounds and anions in environmental matrices. In this method, sample enrichment was achieved through bulk injection and enrichment column collection, which greatly simplified the pretreatment process. The HPLC instrument was connected to the IC instrument using two six-way valves and an enrichment column. The system operation can be divided into four stages: (A) sample loading to the quantitative ring, (B) separation of nitroaromatic compounds and anions, (C) enrichment of anions in an AG20 column, and (D) simultaneous determination of nitroaromatic compounds and anions by HPLC and IC, respectively. The time of the anions flowing out of the C18 column was determined by directly connecting the C18 column to a conductivity detector. Based on the retention times of the anions, the switching time of the six-way valve was optimized to ensure that the anions completely entered the IC column, thereby ensuring the accuracy of the method. During the chromatographic analysis stage, nitroaromatic compounds were separated and analyzed by HPLC system with a mobile phase composed of potassium phosphate buffer (pH 7.0) and acetonitrile (60∶40, v/v) at a flow rate of 1.0 mL/min; in the IC system, the anions were separated and analyzed using a 20 mmol/L sodium hydroxide aqueous solution as the mobile phase under a suppression current of 50 mA. Both anions and nitroaromatic compounds exhibited strong linear correlations within certain concentration ranges, with correlation coefficients greater than 0.993. The recoveries of the nitroaromatic compounds and anions ranged from 88.20% to 105.38% at three spiked levels, with relative standard deviations ranging from 2.0% to 11.5%. The contents of six nitroaromatic compounds and three anions in five surface water and five soil samples were determined using the developed method. Although no nitroaromatic compounds were detected in these samples, the three anions were detected at contents ranging from 0.41 to 55.3 mg/L in surface water samples, and 0.56 to 30.2 mg/kg in soil samples. Methodological validation and actual sample detection demonstrated that the proposed method has a high degree of automation, simple operation, good repeatability, high accuracy, wide applicability, and high sensitivity. Thus, this method is suitable for the rapid determination of chloride, nitrite, nitrate ions and nitroaromatic compounds in soil and water and can be extended to the simultaneous determination of inorganic ions and organic matters in other samples.

Interfacial Tension Hysteresis of Eutectic Gallium‐Indium

AbstractWhen in a pristine state, gallium and its alloys have the largest interfacial tensions of any liquid at room temperature. Nonetheless, applying as little as 0.8 V of electric potential across eutectic gallium indium (EGaIn) placed within aqueous sodium hydroxide (NaOH, or other electrolyte) solution will cause the metal to behave as if its interfacial tension is near zero. The mechanism behind this phenomenon has remained poorly understood because NaOH dissolves the oxide species, making it difficult to directly measure the concentration, thickness, or chemical composition of the film that forms at the interface. In addition, the oxide layers formed are atomically‐thin. Here, it presents a suite of techniques that allow to simultaneously measure both electrical and interfacial properties as a function of applied electric potential, allowing for new insights into the mechanisms, which cause the dramatic decrease in interfacial tension. A key discovery from this work is that the interfacial tension displays hysteresis while lowering the applied potential. It combines these observations with electrochemical impedance spectroscopy to evaluate how these changes in interfacial tension arise from chemical, electrical, and mechanical changes on the interface, and close with ideas for how to build a free energy model to predict these changes from first principles.

Spatiotemporally resolved characterization for analyzing the interfacial behaviors of gelation in aqueous phase separation

Precipitating polymer in a completely aqueous environment is conceptualized as a process of aqueous phase separation (APS) and lends itself to the environmentally friendly fabrication of membranes. In an effort to effectively regulate the morphological formation in APS, it is of fundamental concern to elucidate how asymmetry can be developed in the absence of an unbalanced exchange of the ‘nonsolvent’ and solvent. Therefore, technical modifications were made by this study to essentially improve the in-situ characterization based on optical coherence tomography (OCT). In particular, a process of APS was modeled by passively contacting an acidic aqueous dope of chitosan with another aqueous solution of sodium hydroxide in a mini-coagulation bath, where the OCT scan was implemented in a high speed mode to capture the onset and evolution of gelation at the coagulant-dope interface with a temporal resolution of 6.25 ms. The quantitative analysis indicated that the gelation could be initiated at the interface in a period shorter than ∼10 ms and evolved in an oscillating way; a skin layer with a smaller critical size would be formed by damping the interfacial oscillations. This study not only sheds light on the APS-based fabrication of membranes, but also establishes a novel paradigm for in-situ characterizing the film formation via an OCT-based approach.