Acidic Aqueous Solution Research Articles

Pharmacokinetics of Anti-Rheumatic drugs Methotrexate and Tofacitinib with its metabolite M9 in Rats by UPLC-MS/MS.

Tofacitinib is an oral JAK inhibitor for the treatment of rheumatoid arthritis (RA). The clinical efficacy and safety of an administered tofacitinib, either monotherapy or in combination with conventional synthetic disease-modifying anti-rheumatic drugs, mainly methotrexate (MTX), have been evaluated. The high plasma concentration with delayed medicine clearance may affect the liver and/or kidney functions. In this study, an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC- MS/MS) method for the quantitative analysis of methotrexate, tofacitinib, and metabolite M9 in plasma of Sprague Dawley (SD) rats was developed, and its effectiveness was validated as well. Methotrexate, tofacitinib, M9 and fedratinib (internal standard, IS) were separated by gradient elution. The chromatography was performed on an Acquity BEH C18 (2.1 mm × 50 mm, 1.7 μm) column with the mobile phases of acetonitrile and 0.1% formic acid aqueous solution with different proportions at the flow rate of 0.30 mL/min. In the positive ionization mode, the analyzes were detected using a Xevo TQ-S triple quadrupole tandem mass spectrometer, with the following mass transition pairs: m/z 313.12 → 148.97 for tofacitinib, m/z 329.10 → 165.00 for M9 and m/z 455.12 → 308.05 for methotrexate. The obtained results manifested good calibration linearity over the ranges of tofacitinib at 0.1-100 ng/mL, M9 at 0.05-100 ng/mL, and methotrexate at 0.05-100 ng/mL. The lower limit of quantifications (LLOQs) of methotrexate, tofacitinib and M9 were 0.05 ng/mL, 0.1 ng/mL and 0.05 ng/mL, respectively. Intra-day and inter-day accuracy values were confirmed with a range of -6.3% to 12.7%, while intra-day and inter-- day precision values were ≤14.4%. Additionally, recoveries were greater than 86.5% for each compound without significant matrix effects. The currently established analytical method exhibited great potential for the evaluation of plasma concentrations of methotrexate, tofacitinib and M9 simultaneously, greatly reducing the detection time, which would serve as a supplementary role in formulating dose decisions to achieve personalized treatment, identify drugs that cause adverse reactions and finally, to assess drug-drug interactions on clinical studies.

In English

The synthesis and characterization of heterostructure por-Ga2O3/GaAs represent a crucial advancement in nanomaterials, particularly in optoelectronic applications. Employing a two-stage electrochemical etching methodology, this research has elucidated the precise conditions required to fabricate such a heterostructure. The initial stage involves etching monocrystalline gallium arsenide (GaAs) using an aqueous nitric acid solution as the electrolyte. This process is governed by the redox reactions at the crystal-electrolyte interface, where GaAs are partially oxidized and selectively etched. The second stage introduces ethanol into the electrolytic solution. This chemical addition serves a dual purpose: Firstly, it modulates the electrochemical environment, allowing for controlling pore morphology in GaAs. Secondly, it facilitates the etching of the resultant oxide layer, which predominantly consists of gallium oxide (Ga2O3). The formation of this oxide layer can be attributed to the oxidation of GaAs, driven by the electrochemical potentials and resulting in the deposition of reaction by-products on the substrate surface. The fabricated nanocomposite was comprehensively characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), and Raman Spectroscopy. SEM imaging revealed a range of agglomerated nanostructures dispersed across the surface, with dimensions ranging from 8–25 μm, 1–1.5 μm, and 70–100 nm. These observations suggest a hierarchical pore structure indicative of a complex etching mechanism modulated by the electrolyte composition. Raman spectroscopic analysis corroborated the presence of various phases in the heterostructure. Signals corresponding to bulk GaAs, serving as the substrate, were distinguishable. In addition, peaks indicative of porous GaAs and porous Ga2O3 were observed. A cubic phase in the Ga2O3 layer was particularly noteworthy, suggesting a higher degree of crystallinity. Notably, the absence of Raman-active modes associated with internal stresses implies that the fabricated heterostructure is of high quality.

Quantification and analyses of seven tyrosine kinase inhibitors targeting hepatocellular carcinoma in human plasma by QuEChERS and UPLC-MS/MS

Tyrosine kinase inhibitors (TKIs) are commonly used to treat various cancers. Literature suggests that the blood concentration of TKIs strongly correlates with their efficacy and adverse effects. Therefore, establishing a Therapeutic Drug Monitoring (TDM) methodology for TKI drugs is crucial to improving their clinical efficacy and minimizing the treatment-related adverse effects. However, quantifying their concentrations in the plasma using existing methods to avoid potential toxicity is challenging. Herein, seven TKIs, namely sorafenib tosylate, axitinib, erlotinib, cediranib, brivanib, linifanib, and golvatinib, were successfully analyzed in human plasma by following a quick, easy, cheap, effective, rugged, and safe (QuEChERS) pretreatment method combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Briefly, biological samples were extracted using 1 mL of methanol, followed by the sequential addition of 250 mg of anhydrous magnesium sulfate and 25 mg of N-propylethylenediamine (PSA) for salinization and purification by adsorption, respectively. In this study, dovitinib was used as the internal standard. The seven TKIs were detected by the gradient elution method for 4 min in the positive ion electrospray mode. The mobile phase comprised methanol (phase A) and 0.1 % aqueous formic acid solution (phase B) on the Agilent Zorbax RRHD Stablebond Aq, (2.1 × 50 mm; 1.8 μm). Brivanib, linifanib, axitinib, sorafenib tosylate, and golvatinib exhibited good linearity in the range of 5–500 ng/mL, and erlotinib and cediranib exhibited good linearity in the range of 10–1000 ng/mL, with linear correlation coefficients (R2) ≥ 0.99. The limits of detection and quantification were 0.60–0.18 ng/mL and 5–10 ng/mL, respectively. The intraday and interday accuracy values ranged from −6.12 % to 7.31 %, with a precision (RSD) of ≤ 10.57 %. The method was rapid, accurate, specific, simple, reproducible, and suitable for the quantitative determination of the seven TKIs in human plasma.

The Study of the Sense of Smell in Children: Development Prospects

Background. Despite the fact that the study of the olfactory system is still difficult, the detection of dysosmia is promising for the diagnosis of a number of diseases. As a screening method, tests for the identification of various odors can be used. However, similar tests are developed and used for adults. In pediatrics, the use of such methods causes difficulty due to the cognitive and linguistic functions of the child, which are in the stage of development. Aim — to study olfactory function in children using an identification test. Methods. A diagnostic prospective study of 30 healthy children with no complaints of decreased olfactory function, living in the middle zone of the Russian Federation, mainly in the Moscow Metropolitan area, aged 11 to 14 y.o. was held. All children underwent a study of olfactory function using the University of Pennsylvania Smell Identification Test (UPSIT). To control all children, olfactometry was performed using a patented method for assessing the thresholds of olfaction in children, based on the use of various concentrations of aqueous solutions of valerian tincture, ammonia and acetic acid. Results. In the study of sense of smell with the help of an UPSIT test, hyposmia was detected in 30% of children, which was not confirmed later with the help of a threshold test. At the same time, when presenting some odorants, most of the answers were incorrect. Conclusions. The use of olfactory tests developed for adults in children does not reflect the real state of the olfactory system. It is required to create kits for the study of the olfactory function specifically for the children’s category of patients.

A comparative study of electrochemical reduction of levulinic acid on various electrodes in organic solvents

Studies on the electrochemical hydrogenation (ECH) of levulinic acid (LA) to valeric acid (VA) or γ‐valerolactone (GVL) have mainly focused on the electroreduction of LA in acidic aqueous solutions. However, the narrow range of applied potentials has hindered understanding of some mechanistic aspects of LA electrochemical conversion. Earlier, we discovered that employing proton‐deficient non‐aqueous reaction media provides more comprehensive insights into the mechanism of LA electrochemical reduction. Here, we conducted further investigations into the LA electroreduction process using cyclic voltammetry in various organic solvents on a Pt electrode and on various electrode materials in acetonitrile, both with and without the addition of proton donors. The products of the ECH processes were identified using HPLC. The solvent nature, the presence of proton donors, the electrode material, and the applied potential strongly influence the LA electroreduction process. This study reveals that LA, in the presence proton donors, can undergo electroreduction through different pathways, depending on the difference (ΔE1/2) between the reduction half‐wave potential of protons and LA. When the difference is large, the LA reduction is incomplete and the formation of GVL is observed. Under the close reduction potentials of protons and LA, LA can be completely reduced to VA.

Highly efficient and selective removal of U(VI) from acidic aqueous solution by chitosan/fluorapatite composite

Highly efficient and selective removal of U(VI) from acidic aqueous solution by chitosan/fluorapatite composite

Pharmacokinetics and Tissue Distribution of Itampolin A following Intragastric and Intravenous Administration in Rats Using Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry.

Itampolin A, a natural brominated tyrosine alkaloid isolated from the sponge Iotrochota purpurea, has been shown to have good inhibitory effects in lung cancer cells as a p38α inhibitor. A simple, sensitive, and reliable ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method has been established, validated, and applied to the study of the pharmacokinetics and tissue distribution of itampolin A following intragastric and intravenous administration. Itampolin A and theophylline (internal standard, IS) were extracted by the simple protein precipitation technique using methanol as the precipitating solvent. Chromatographic separation was achieved by using the optimized mobile phase of a 0.1% formic acid aqueous solution and acetonitrile in the gradient elution mode. Itampolin A and IS were detected and quantified using positive electrospray ionization in the multiple reaction monitoring mode with transitions of m/z 863.9 → 569.1 for itampolin A and m/z 181.1 → 124.1 for IS, respectively. The assay exhibited a linear dynamic range of 1-1600 ng/mL for itampolin A in biological samples and the low limit of quantification was 1 ng/mL. Non-compartmental pharmacokinetic parameters indicated that itampolin A was well-absorbed into the systemic circulation and rapidly eliminated after administration. The apparent distribution volume of itampolin A was much higher after intragastric administration than that after intravenous administration. A tissue distribution study showed that itampolin A could be detected in different tissues and maintained a high concentration in the lung, which provided a material basis for its effective application in lung cancer. The pharmacokinetic process and tissue distribution characteristics of imtapolin A were expounded in this study, which can provide beneficial information for the further research and clinical application of itampolin A.

{SeO2(OH)} Bridging Lanthanide-Containing Antimono-Seleno-Tungstates.

A series of new trigonal pyramidal {SeO2(OH)} bridging lanthanide-containing antimono-seleno-tungstates [H2N(CH3)2]8Na8Cs4H9[Ln2SeW4O11(OH)(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33)]2·32H2O [Ln = Tb (1), Dy (2), Ho (3), Er (4)] have been prepared by the synthetic strategy of simultaneously using the antimonotungstate precursor and simple material in an acidic aqueous solution and structurally characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR spectrometry, and thermogravimetric analysis. Their molecular structures contain an unprecedented hexameric polyoxoanion [Ln2SeW4O11(OH)(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33)]229- constituted by two equivalent trimeric subunits Ln2W4O9(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33) bridged via two μ2-{SeO2(OH)} linkers. Furthermore, the catalytic oxidation of various aromatic sulfides and sulfur mustard simulant 2-chloroethyl ethyl sulfide (CEES) by compound 3 as the heterogeneous catalyst has been investigated, exhibiting high conversion and selectivity as well as good stability and recyclability.

Influence of acidity and alkalinity of water environment on water stability of asphalt mixture: Phase II-microscopic erosion mechanism

Acidity and alkalinity of water environments have been proven to influence the water stability of asphalt mixture. However, the relevant influencing mechanism still remains unclear. To fulfill this research gap, this study conducted a series of microscopic tests, aiming at unveiling the microscopic erosion mechanism of the water environment on the water stability of asphalt mixture for better moisture stability achieved. Specifically, the asphalt-aggregate interfacial transition zone (ITZ) samples were prepared by combining #70 asphalt with limestone and granite, respectively, which were then immersed in water solutions at 3 different pH levels (pH = 3.0, 7.0, and 11.0) for 7 days. The chemical composition and microstructure of the asphalt film on the surface of the ITZ samples pre and post-treatment were scrutinized using the Fourier Transform Infrared Spectroscopy (FTIR) and the Atomic Force Microscope (AFM), while the development of microcracks at the asphalt-aggregate interface were identified and traced utilizing the Scanning Electron Microscope (SEM). The test results indicate that after treatment with acidic and alkaline aqueous solutions, the asphalt film's surface is enriched with polar components such as asphaltenes, resins, and aromatic fractions. The migration of these polar components to the surface of the asphalt film reduces the adhesion between asphalt-aggregate, leading to the formation of microcracks at the asphalt-aggregate interface. The most severe crack development occurs in alkaline water environment, followed by acidic water environment. It is interestingly noted that the adhesion at the asphalt-granite interface is improved under the acidic environment. This improvement may be attributed to the covalent nature of silica, which hinders the adsorption of ions from acidic solution into the asphalt film. This hindrance effectively prevents water intrusion at the asphalt-aggregate interface, thereby reducing the adhesion loss. These findings can help elucidate the mechanism of water damage in asphalt pavement exposed to real-world conditions and enhance its water stability with effective countermeasures proposed.

Understanding of lactobionic acid in aqueous-glycol mixtures at different temperatures: Ultrasonic investigation and spectroscopic study

The proposed investigation focused on the study of liquid mixtures that contain polyethylene glycols (PEGs) such as polyethylene glycol-200 and polyethylene glycol-400, and lactobionic acid aqueous solutions. The study aimed to examine the density and ultrasonic speed of these mixtures at different temperatures (288.15 K, 298.15 K, 308.15 K, and 318.15 K) and concentrations (0.01, 0.02 and 0.03) mol.kg-1 of lactobionic acid in aqueous medium. The experimental data obtained were used to estimate various density and sound-speed characteristics, and to calculate the apparent molar, partial molar, and transfer properties of volume and isentropic compressions, including (Vϕ, Vϕ0, ΔVϕ0 and Kϕ,s,Kϕ,s0, ΔKϕ,s0). The interaction coefficients (VAB, VABB, KAB and KABB) were determined using the values of ΔVϕ0and ΔKϕ,s0. Additionally, the study computed the limiting apparent molar expansibilities, its derivative, and empirical parameters. The findings of the study were evaluated in terms of interactions among the solutes and solvents in the liquid mixtures. Moreover, the spectroscopic study of the binary mixture of lactobionic acid and water at different their concentrations was done to find the different stretching and bonds available in the mixture.

Synthesis and characterization of novel quinaldic acid based Ni, Fe, and Cr Complexes: A computational and experimental study

Complexes ([Ni(quin-2-c)2(H2O)2]•2H2O, [Fe(quin-2-c)2(H2O)2], [Cr(quin-2-c)2(H2O)2] were synthesized from aqueous solutions of metal salts, quinaldic acid, and semicarbazide. In the crystal structure of the first complex, the nickel atom is chelated by the deprotonated quinaldic acid molecule through the oxygen atom of the carboxyl group, and the heterocyclic nitrogen atom, as well as two water molecules, are coordinated. The other two water molecules are located in the outer sphere. In the structure of the iron and chromium complexes, the metal atoms have a similar complex formation but do not have water molecules in the outer sphere. In all compounds, quinaldic acid acts as a bidentate ligand to form five-membered metallocycles. The electronic structure properties were investigated through theoretical modeling using the B3LYP method at the 6–31 + G(d,p) computational level. Density functional theory (DFT) was employed in quantum chemistry simulations to refine proposed structures and explore the characteristics of frontier orbitals via analysis of frontier molecular orbitals (FMOs). These computations facilitated the identification of specific sites on the surface of molecules by generating molecular electrostatic potential maps and provided insights into the structural and reactive properties. Hirshfeld surface analysis was conducted to examine intermolecular interactions, revealing a prevalence of H⋅⋅⋅H interactions.

Autoclaving Achieves pH-Neutralization, Hydrogelation, and Sterilization of Chitosan Hydrogels in One Step

Conventionally, chitosan hydrogels are acidic and contain toxic chemicals because chitosan is soluble only in acidic solvents and requires toxic additives such as chemical crosslinkers and polymerization agents to fabricate chitosan hydrogels. These properties prevent chitosan hydrogels from being used for medical applications. In this study, chitosan hydrogels were prepared by a simple and versatile process using urea hydrolysis by autoclaving (steam sterilization, 121 °C, 20 min). When autoclaved, urea hydrolyzes in an acidic chitosan aqueous solution, and ammonia is produced, which increases the pH of the solution, and chitosan becomes insoluble, leading to the formation of a chitosan hydrogel. The pH and osmotic concentration of chitosan hydrogels could be adjusted to be suitable for physiological conditions (pH: 7.0–7.5, and osmotic concentration: 276–329 mOsm/L) by changing the amount of urea added to chitosan solutions (chitosan: 2.5% (w/v), urea: 0.75–1.0% (w/v), pH: 5.5). The hydrogels had extremely low cytotoxicity without the washing process. In addition, not only pure chitosan hydrogels, but also chitosan derivative hydrogels were prepared using this method. The autoclaving technique for preparing low-toxic and wash-free sterilized chitosan hydrogels in a single step is practical for medical applications.

Nucleation of Methane Hydrate from Water and Aqueous Solutions of Malonic Acid in Glass Cells with Varying Surface Hydrophilicity

Nucleation of Methane Hydrate from Water and Aqueous Solutions of Malonic Acid in Glass Cells with Varying Surface Hydrophilicity

Synthesis of Nano-electrolytic Manganese Dioxide for Alkaline Batteries Mediated by Organic Additives

This article discusses the impact of adding organic additives like glycine (GLY), sucrose (SUC), and saccharine (SACCH) on the electrical characteristics and microstructure of electrolytic manganese dioxide (EMD), which is made from an acidic aqueous sulphate solution. The structure and chemistry of EMD were ascertained by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). To assess the material's potential for use in alkaline batteries, its charge-discharge properties were ascertained. It was found that the majority of MnO2 in all the EMD samples was in the γ-phase, which is electrochemically active and useful for energy storage applications. When glycine, sucrose, and saccharine were added to the solution as organic additives, the electrochemical deposition of manganese dioxide (MnO2) resulted in an increase in current efficiency and a decrease in energy consumption. The SEM images demonstrated that when EMD was deposited with an additive, small grain sizes and discrete particles free of agglomeration were formed, but large grain sizes were obtained in the absence of additives. Charge-discharge characteristics suggested that the additions improve the ability of MnO2 structure to store energy. This suggested that the additions may have an impact on the morphology and size of the particles, and consequently, the electrochemical activities of the material that was electrodeposited. In the case of the additives examined in this paper, the outcome was the creation of a material with possible use in battery technology.

Tribocorrosion Evaluation of AISI 431 Coated With Tungsten Oxynitride

Abstract Tribocorrosion is a phenomenon present in a wide variety of processes; hence, understanding the tribocorrosion behavior of different systems is essential to being able to design robust and reliable systems. This has led us to investigate the tribocorrosion behavior of AISI 431 steel, a stainless steel commonly used for manufacturing mechanical pieces. The response to tribocorrosion was evaluated for the AISI 431 steel in contact with an aqueous solution of citric acid, a solution commonly used in the food industry. The tests were carried out using samples of steel uncoated and coated with tungsten oxynitride in a pin-on-disc configuration using a tailored tribocorrosion cell. The uncoated AISI 431 presented good wear and corrosion resistance but presented tribocorrosion degradation, where the growth of the passivation film and the mechanical removal of such film were the driving factors for the tribocorrosion process. Furthermore, when the steel was coated with the tungsten oxynitride film, we found that the surface presented a better resistance to wear, corrosion, and tribocorrosion. Such findings open a great opportunity for the use of these types of coatings to protect systems against tribocorrosion.

Efficient Capture and Electroreduction of Dilute CO2 into Highly Pure and Concentrated Formic Acid Aqueous Solution.

High-purity CO2 rather than dilute CO2 (15 vol %, CO2/N2/O2 = 15:80:5, v/v/v) similar to the flue gas is currently used as the feedstock for the electroreduction of CO2, and the liquid products are usually mixed up with the cathode electrolyte, resulting in high product separation costs. In this work, we showed that a microporous conductive Bi-based metal-organic framework (Bi-HHTP, HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) can not only efficiently capture CO2 from the dilute CO2 under high humidity but also catalyze the electroreduction of the adsorbed CO2 into formic acid with a high current density of 80 mA cm-2 and a Faradaic efficiency of 90% at a very low cell voltage of 2.6 V. Importantly, the performance in a dilute CO2 atmosphere was close to that under a high-purity CO2 atmosphere. This is the first catalyst that can maintain exceptional eCO2RR performance in the presence of both O2 and N2. Moreover, by using dilute CO2 as the feedstock, a 1 cm-2 working electrode coating with Bi-HHTP can continuously produce a 200 mM formic acid aqueous solution with a relative purity of 100% for at least 30 h in a membrane electrode assembly (MEA) electrolyzer. The product does not contain electrolytes, and such a highly concentrated and pure formic acid aqueous solution can be directly used as an electrolyte for formic acid fuel cells. Comprehensive studies revealed that such a high performance might be ascribed to the CO2 capture ability of the micropores on Bi-HHTP and the lower Gibbs free energy of formation of the key intermediate *OCHO on the open Bi sites.

Sorption Characteristics and Chromatographic Separation of 90Y3+ from 90Sr2+ from Aqueous Media by Chelex-100 (Anion Ion Exchange) Packed Column.

There is growing demand for separation of 90Y carrier free from 90Sr coexisting to produce high purity 90Y essential for radiopharmaceutical uses. Thus, in this context the sorption profiles of Y3+ and Sr2+ from aqueous solutions containing diethylenetriaminepenta acetic acid (DTPA), ethylenediaminetetra-acetic acid (EDTA), acetic acid, citric acid, or NaCl onto Chelex-100 (anion ion exchange) solid sorbent were critically studied for developing an efficient and low-cost methodology for selective separation of Y3+ from Sr2+ ions (1.0 × 10-5 M). Batch experiments displayed relative chemical extraction percentage (98 ± 5.4%) of Y3+ from aqueous acetic acid solution onto Chelex-100 (anion ion exchanger), whereas Sr2+ species showed no sorption. Hence, a selective separation of Y3+ from its parent 90Sr2+ has been established based upon percolation of the aqueous solution of Y3+ and Sr2+ ions containing acetic acid at pH 1-2 through Chelex-100 sorbent packed column at a 2 mL min-1 flow rate. Y3+ species were retained quantitatively while Sr2+ ions were not sorbed and passed through the sorbent packed column without extraction. The sorbed Y3+ species were then recovered from the sorbent packed column with HNO3 (1.0 M) at a 1.0 mL min-1 flow rate. A dual extraction mechanism comprising absorption associated to "weak-base anion exchanger" and "solvent extraction" of Y3+ as (YCl6)3- and an extra part for "surface adsorption" of Y3+ by the sorbent is proposed. The established method was validated by measuring the radiochemical (99.2 ± 2 1%), radionuclide purity and retardation factor (Rf = 10.0 ± 0.1 cm) of 90Y3+ recovered in the eluate. Ultimately, the sorbent packed column also presented high stability for reusing 2-3 cycles without drop in its efficiency (±5%) towards Y3+ uptake and relative chemical recovery. A proposed flow sheet describing the analytical procedures for the separation of 90Y3+ from 90Sr2+ using chelating Chelex 100 (anion exchange) packed column is also included.

Determination of stearic acid and 12-hydroxyoctadecanoic acid in PEG-60 hydrogenated castor oil by HPLC-ELSD after alkaline hydrolysis

AbstractA rapid and simple method for the determination of stearic acid and 12-hydroxystearic acid in PEG-60 hydrogenated castor oil by high performance liquid chromatography with evaporative light scattering detection was established. The oil sample was first pretreated by alkaline hydrolysis. The analysis was performed on a Zhongpu Develop XD-C18 column (250 mm × 4.6 mm, 5 µm) with gradient elution of methanol and 1% acetic acid aqueous solution at a flow rate of 1.2 mL·min−1 and a column temperature of 40 °C. The drift tube temperature of the evaporative light scattering detection system was set at 40 °C, and the pressure of carrier gas (N2) was 337 kPa. The regression equation revealed a good linear relation (r = 0.9993–0.9995) during the test ranges (119.1–1190.7 μg·mL−1 for 12-hydroxystearic acid, 10.7–107.4 μg·mL−1 for stearic acid). The detection limits of 12-hydroxystearic acid and stearic acid were 1.1 and 2.5 μg·mL−1, the limits of quantitation were 3.2 and 7.4 μg·mL−1, respectively. And the mean recoveries were 101.5 and 101.0%, the corresponding relative standard deviations (RSDs) were 2.1 and 2.8%, respectively. The RSDs corresponding to repeatability (n = 6) were both less than 1.7% in terms of precision. As to the stability, the test results remained stable after 8 h at room temperature (RSDs were both less than 2.6%). The developed method showed high sensitivity, recovery, repeatability and stability, which indicated that the method could be applied as a quality evaluation method for the determination of stearic acid and 12-hydroxyoctadecanoic acid in PEG-60 hydrogenated castor oil.

Improved determination of nitrate isotopes in irrigated agricultural areas and Bayesian mixing model quantification of nitrate sources and fate

Technological advancements in isotope techniques have been widely utilized in environmental pollution research, particularly for the monitoring of nitrate pollution in water. The utilization of pretreatment with an aqueous nitric acid solution offers numerous advantages in analyzing isotopic composition; however, there is still room for improvement regarding conversion efficiency, reduced reaction time, and cost control. In light of this, this study proposes an enhanced chemical conversion method that involves mitigating the interference caused by the nitrogen azide reaction during the pretreatment process, optimizing the purge gas to remove interfering factors, and improving the inlet device for measuring nitrous oxide. The improved method was applied to determine nitrate isotopes in the Ulansuhai Basin, Inner Mongolia and its reliability was verified through analytical results obtained from bacterial denitrification methods. The mean δ15N-NO3- and δ18O-NO3- values determined using the chemical transformation method were 4.85‰ and 23.44‰, respectively. Compared with the previous method, the improved method enhanced the maneuverability of precise control, the pretreatment time was reduced from 2 to 3 hours to 1.5 hours, and the experimental cost was scaled down to half of the original one. In addition, the contribution of each source was calculated by combining nitrate isotopes with a Bayesian stable isotope mixing model. It was found that manure sewage accounted for (50.1±22.6) % while soil nitrogen sources contributed (25.1±20.4) % to nitrate levels in Ulansuhai Lake's water. The chemical conversion methods successfully improved within this study can also be applied to other watersheds or regions. These research findings provide a valuable theoretical foundation for managing nitrogen sources within watersheds.

Al-water reaction generates metastable aluminum cluster ions and their use in advanced oxidation processes

Our previous work indicated that hydroxyl radicals (HO•) exist in the filtrate of Al + acid + H2O2 system. In this work, the behind mechanism was investigated in detail and a new catalyst for advanced oxidation processes (AOPs) was found for the first time. It was revealed that metastable hexacoordinated aluminum cluster ions ([Al(H2O)63+]*), which are produced by Al-water reaction, can be as direct catalyst and decompose H2O2 into HO• in a full pH range (2.5–12.0), and efficiently degrade and mineralize organic pollutants without precipitates. Of course, their catalytic activity in acidic aqueous solution is higher than that in neutral and alkaline solutions. Furthermore, [Al(H2O)63+]* cluster ions have an excellent recyclability and their catalytic efficiency for generating HO• and degrading phenol and bisphenol A (BPA) did not decrease significantly even the cycling number was up to ten. Meanwhile, [Al(H2O)63+]* cluster ions have a long lifetime and can keep their catalytic activity for more than three months under ambient condition. The present finding shows that Al3+ ions can be also as a cost-efficient catalyst for AOP technology.