Stream Of Nitrogen Research Articles

Upcycling Postconsumer High-Density Polyethylene (PC-HDPE): Thermal Stability and Kinetics Study of the Filaments Extruded from PC-HDPE

Thermal stability and kinetics of thermolysis of postconsumer milk containers made of high-density polyethylene (PC-HDPE) and filament rods extruded from them (HDPE-F) were examined by thermogravimetric analysis (TGA) with six linear temperature programs under a stream of nitrogen. The total weightloss of each sample took place in a one-step decomposition to volatiles at the heating rates, β = 1, 10, 25, 50, 70, and 100 Kmin-1. The values of initial decomposition temperature, the temperature at the maximum thermal degradation rate, and the maximum rate of decomposition were increased by increasing the heating rate as was the expectation. The isoconversional method was used to evaluate the fundamental kinetic parameters, the activation energy barrier (Ea ), the Arrhenius pre-exponential factor (A), and the mechanism of the reaction, f(α). The values of Ea were independent of the model and heating rate, as was expected. However, the values of A depended on the model and the extent of reaction (α). The values of the Ea of PC-HDPE initiated at 171 kJ/mol at α = 0.05 and it increased to 207 kJ/mole at α = 0.95. The values of Ea of the HDPE-F rod were relatively constant for all α values, being 227 ± 3 kJ/mol. It was justified by the absence of easily volatilized substances in the HDPE-F. Knowledge of the thermal stability and decomposition kinetics of the starting materials (PC-HDPE) and the product (HDPE-F) is important in the context of thermochemical conversion processes aimed at the use of PC-HDPE as raw materials for recycling, upcycling, and down-cycling for objects used under room conditions.

Development, validation of a GC–MS method for the simultaneous measurement of amino acids, their PTM metabolites and AGEs in human urine, and application to the bi-ethnic ASOS study with special emphasis to lysine

A gas chromatography-mass spectrometry (GC–MS) method was developed and validated in relevant concentration ranges for the simultaneous measurement of l-lysine (Lys, L) and its Nε- and Nα-methylated (M), Nε- and Nα-acetylated (Ac), Nε-carboxymethylated (CM) and Nε-carboxyethylated (CE) metabolites in human urine. Analyzed Lys metabolites were the post-translational modification (PTM) products Nε-mono-, di- and trimethyllsine, Nε-MML, Nε-DML, Nε-TML, respectively, Nα-ML, Nε-AcL, Nα-AcL, and its advanced glycation end-products (AGEs) Nε-CML, Nε-CM-[2,4,4-2H3]Lys (d3-CML), Nε-CEL and furosine. AGEs of arginine (Arg) and cysteine (Cys) were also analyzed. De novo synthesized trideutero-methyl esters (R-COOCD3) from unlabelled amino acids and derivatives were used as internal standards. Native urine samples (10 µL aliquots) were evaporated to dryness under a stream of nitrogen. Analytes were esterified using 2 M HCl in methanol (60 min, 80 °C) and subsequently amidated by pentafluoropropionic anhydride in ethyl acetate (30 min, 65 °C). The generated methyl ester-pentafluoropropionyl (Me-PFP) derivatives were reconstituted in borate buffer and extracted immediately with toluene. GC–MS analyses were performed by split-less injection of 1-µL aliquots, oven-programmed separation and negative-ion chemical ionization (NICI). Mass spectra were generated in the scan mode (range, m/z 50–1000). Quantification was performed in the selected-ion monitoring (SIM) mode using a dwell time of 50 or 100 ms for each ion. The GC–MS method was suitable for the measurement of Lys and all of its metabolites, except for the quaternary ammonium cation Nε-TML. The Me-PFP derivatives of Lys, Arg and Cys and its metabolites eluted in the retention time window of 9 to 14 min. The derivatization of Nε-CML, d3-CML and Nε-CEL was accompanied by partial Nε-decarboxylation and formation of the Me-PFP Lys derivative. The lowest derivatization yield was observed for Nε-DML, indicating a major role of the Nε-DML group in Lys derivatization. The GC–MS method enables precise (relative standard deviation, RSD < 20%) and accurate (bias, < ± 20%) simultaneous measurement of 33 analytes in human urine in relevant concentration ranges. We used the method to measure the urinary excretion rates of Lys and its PTM metabolites and AGEs in healthy black (n = 39) and white (n = 41) boys of the Arterial Stiffness in Offspring Study (ASOS). No remarkable differences were found indicating no ethnic-related differences in PTM metabolites and AGEs except for Nε-monomethyllysine and S-(2-carboxymethylcysteine).

Long-term changes in atmospheric nitrogen deposition and stream water nitrate leaching from forested watersheds in western Japan

Japan receives nitrogenous air pollutants via long-range transport from China. However, emissions of nitrogenous air pollutants in China have stabilized or decreased in recent years. This study examined both the long-term trends in atmospheric nitrogen (N) deposition from the 1990s to the 2010s and the response of stream water nitrate (NO3−) leaching from forested areas in western Japan. A long-term (1992–2018) temporal analysis of atmospheric N deposition in Fukuoka (western Japan) was conducted. Atmospheric bulk N deposition was collected at forested sites in a suburban forest (Swest) and a rural forest (Rwest) in western Japan during 2009–2018. Stream water samples were also collected from four locations at sites Swest and Rwest during the same period. Results showed that atmospheric N deposition in Fukuoka started to decrease from the mid-2000s at an annual rate of −2.5% yr−1. The decrease in atmospheric N deposition was attributable mainly to decreased atmospheric ammonium (NH4+) deposition, which caused greater contribution of NO3− deposition to atmospheric N deposition. Concentrations of NO3− in the stream water samples from three of the four locations decreased significantly at an annual rate of −3.7 to −0.7% yr−1. However, stream water NO3− concentrations increased in one watershed where understory vegetation has been deteriorating owing to the increased deer population. This might weaken the recovery of N leaching from forested areas.

A Cryogenic Test Rig for Dynamically Operated Plate‐Fin Heat Exchangers

AbstractFlexible operation of air separation units may lead to enhanced thermal stress on the main heat exchanger, typically an aluminum plate‐fin heat exchanger. Hence, a large, cryogenic test rig has been built to investigate fatigue effects of dynamic operation. Nitrogen streams at –175 °C and 50 °C are applied to induce a highly repetitive series of temperature changes in two plate‐fin heat exchangers, which are extensively equipped with measurement technology to collect 3D temperature and strain data and to detect the provoked fatigue damages. Results of the measurements will be used to improve computational lifetime estimation tools.

Determination of 18 amino acids in three different kinds of milk powder by ultra performance liquid chromatography coupled with pre-column derivatization

近年来羊奶粉和骆驼奶粉备受消费者青睐,它们具有潜在的低致敏性,因此成为牛乳不耐受人群尤其是婴幼儿的母乳替代品,其营养价值备受关注。牛奶粉、羊奶粉和骆驼奶粉中氨基酸含量的比较研究鲜有报道。利用酸水解得到游离氨基酸,选择6-氨基喹啉-N-羟基琥珀酰亚胺氨基甲酸酯(AQC)进行柱前衍生,超高效液相色谱分离并检测,外标法定量。18种氨基酸在各自线性范围内线性关系良好,相关系数(r 2)大于0.999;以3倍和10倍信噪比(S/N)确定方法的检出限(LOD)和定量限(LOQ),分别为1.3~2.5 (mg/100 g)和3.9~7.5 (mg/100 g)。方法验证采用奶粉标准参考物质SRM 1849a,测定值符合其含量范围,6次测定值的相对标准偏差(RSD)为2.04%~3.65%。采用建立的方法分别对市售和网购的牛奶粉、羊奶粉和骆驼奶粉进行18种氨基酸成分和含量分析,旨在从氨基酸角度对这3种不同来源乳品进行对比。该方法快速,灵敏度高,准确可靠,适用于不同基质乳粉中18种氨基酸成分和含量的确定。

Physical and Numerical Modeling of the Slag Splashing Process.

The influence of technological factors on the process of slag splashing was analyzed in the paper. The problems were solved in several stages using our own and commercial calculation programs and laboratory tests. Based on the performed calculations and simulations, factors affecting the slag splashing were determined. It was observed that the high efficiency of the process can be achieved by optimizing numerous technological parameters, e.g., flow parameters, pressure, and temperature of the nitrogen stream, height and angle of the lance position, as well as slag height into which the gas stream enters and MgO consumption. In addition, the chemical and mineralogical composition of the slag and its physicochemical parameters should be also considered. The obtained results of numerical simulations of slag splashing in the oxygen converter coincide with the results of experiments carried out using the physical model of oxygen converter. This means that the simulations well represent the real course of the slag splashing process for the studied variants.

Increased levels of hexacosanoic acid in the brain of Wistar rats: a behavioral study

Introduction: X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal metabolic disorder associated with mutations in the ATP-binding cassette sub-family D member1 ( ABCD1 ) gene. Practically all male patients with X-ALD develop adrenocortical insufficiency during childhood and progressive myelopathy and peripheral neuropathy in adulthood. However, some male patients develop a fatal cerebral demyelinating disease named cerebral adrenoleukodystrophy. Although the exact mechanisms underlying brain damage in X-ALD are still poorly elucidated, it is known that hexacosanoic acid (C26:0) accumulation represents a hallmark in the pathogenesis of this disease. In this study, we examined whether an overload of C26:0 injected in Wistar rats was capable of causing behavioral changes in these animals. Methods: Egg lecithin in ethanol was dried under a nitrogen stream and mixed with C26:0 methyl ester. Male Wistar rats at 2–3 weeks of age were obtained from Universidade Federal do Rio Grande do Sul (UFRGS), divided into 8 groups, and submitted to an open field test. We then analyzed line crossings (locomotion and exploration), rearing (orienting and investigatory responses), grooming (anxiety manifestation), and latency to move for each animal. Results: Animals subjected to C26:0 administration presented fewer crossings and rearing episodes and a higher latency to move 45 minutes after C26:0 injection. The present work yields experimental evidence that C26:0, the main accumulated metabolite in X-ALD, can cause behavioral alterations in rats such as the impairment of locomotion and exploratory capabilities, as well as a reduction in orienting and investigatory responses. Conclusion: Although our results are preliminary, they are extremely important for future studies that investigate C26:0 accumulation and locomotor impairment in patients with X-ALD.

Simultaneous liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application

A rapid and easy liquid chromatography-tandem mass spectrometry (LC–MS/MS) method was developed, validated, and used to quantify amlodipine besylate and metoprolol succinate in human plasma. Hydrochlorothiazide was used as the internal standard. LC–MS/MS with electrospray ionization in the positive ionization mode was performed under multiple reaction monitoring to examine analytes, which were drawn from human plasma via liquid–liquid extraction using a mixture of diethyl ether and dichloromethane (6:4). The extracts were dried under a nitrogen stream at 40°C, after which the samples were dissolved in a mixture of methanol and water (80:20). The re-dissolved samples were injected onto a C18 column and eluted using a mixture of methanol and 0.4% formic acid (80:20) as the mobile phase. Linear standard calibration was performed, and lower limits of quantification were determined for each analyte. The developedmethod was fully validated with respect to selectivity and carryover, as well as intra-and inter-day accuracy and precision in accordance with guidelines of the United StateFood and Drug Administration and the European Medicines Agency. Mean analyte recovery was between 71.72% and 97.55%, and matrix effects exerted only a minor influence on precision.The validated method was applied in aclinicalbioequivalence study to evaluate the in vivo bioequivalence of twocommer-cialproducts containing 5 mg amlodipine and 50 mg metoprolol. This randomized, single-dose, two-treatment, three-period, two-sequence, open-label, crossover study involved 14 healthy subjects, and a two-week washout period between the two phases of the research was implemented. Standard pharmacokinetic parameters were calculated to compare a test product with Selomax®as the reference. How to Cite this Article Pubmed Style Tuyen NTL, Nghiem LQ, Tuan ND. liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application. SRP. 2019; 10(2): 1-7. doi:10.5530/srp.2019.2.01 Web Style Tuyen NTL, Nghiem LQ, Tuan ND. liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application. http://www.sysrevpharm.org/?mno=302644896 [Access: March 31, 2021]. doi:10.5530/srp.2019.2.01 AMA (American Medical Association) Style Tuyen NTL, Nghiem LQ, Tuan ND. liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application. SRP. 2019; 10(2): 1-7. doi:10.5530/srp.2019.2.01 Vancouver/ICMJE Style Tuyen NTL, Nghiem LQ, Tuan ND. liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application. SRP. (2019), [cited March 31, 2021]; 10(2): 1-7. doi:10.5530/srp.2019.2.01 Harvard Style Tuyen, N. T. L., Nghiem, . L. Q. & Tuan, . N. D. (2019) liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application. SRP, 10 (2), 1-7. doi:10.5530/srp.2019.2.01 Turabian Style Tuyen, Nguyen Thi Linh, Le Quan Nghiem, and Nguyen Duc Tuan. 2019. liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and Reviews in Pharmacy, 10 (2), 1-7. doi:10.5530/srp.2019.2.01 Chicago Style Tuyen, Nguyen Thi Linh, Le Quan Nghiem, and Nguyen Duc Tuan. Simultaneous liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application. Systematic Reviews in Pharmacy 10 (2019), 1-7. doi:10.5530/srp.2019.2.01 MLA (The Modern Language Association) Style Tuyen, Nguyen Thi Linh, Le Quan Nghiem, and Nguyen Duc Tuan. Simultaneous liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and application. Systematic Reviews in Pharmacy 10.2 (2019), 1-7. Print. doi:10.5530/srp.2019.2.01 APA (American Psychological Association) Style Tuyen, N. T. L., Nghiem, . L. Q. & Tuan, . N. D. (2019) liquid chromatography-tandem mass spectrometry assay of amlodipine besylate and metoprolol succinate in human plasma: Development, validation, and Reviews in Pharmacy, 10 (2), 1-7. doi:10.5530/srp.2019.2.01

Wear under brittle removal regime of an under-expanded cryogenic nitrogen jet machining of bio-composites

Machining of biocomposites using traditional techniques has shown some limitations due to the multiscale complex cellulosic structure of natural fibrous reinforcement. This paper aims to demonstrate the feasibility of the cryogenic nitrogen jet, which is a novel cutting process that combines sustainable resources and cryogenic temperatures from −175 °C to 150 °C, as a machining process for biocomposites made of unidirectional flax fibers and polylactic-acid polymer (PLA). A high-velocity stream of liquid nitrogen with and without abrasives (400–700 m/s) is hence directed onto the workpiece surface. For the abrasive jet, both conventional garnet abrasives and bio-based abrasives made from walnut shells were used for the nitrogen jet process. The kerf depth, which is representative of the erosion wear mechanisms, was calculated to assess the erosion rate of the biocomposite structure after the nitrogen jet cutting operation. Then, scanning electron microscope observations are performed to characterize the induced damages on the machined biocomposite surfaces. Results show that the pressure and the traverse speed of the nitrogen jet are the relevant process parameters that control the mechanical and thermal stresses viewed by the biocomposite during the machining operation. Each impinging abrasive particle removes a small amount of biocomposite material during the jet cutting process, which depends on the brittleness of the anisotropic work structure and the abrasiveness of the incorporated particles into the jet stream.

Synthesis and characterization of magnetic activated carbon from Ceiba pentandra fiber for zinc ion removal

One of the heavy metals contained in the electroplating industrial wastewater is zinc. Adsorption is found to be one of the most effective methods for zinc ion removal from aqueous solution due to low cost and simple to operate. The main purpose of this study was to use cotton (Ceiba pentandra) fiber as a precursor to developing a magnetic activated carbon (MAC) for zinc ion removal. The activation process was carried out using potassium hydroxide (KOH) by conventional heating using a tubular furnace at a temperature of 500°C for 2 hours under a stream of nitrogen (N2), while the magnetization process was carried out using co-precipitation method. The adsorption of zinc ion onto MAC was recorded to be 96% at a solution pH of 5 and contact time of 180 min. The adsorption of zinc onto AC is fitted well by the Freundlich isotherm model, while the zinc-MAC system is described well by the Langmuir isotherm model. Meanwhile, the pseudo second order kinetic model is suitable for AC and MAC. Owing to low cost and high efficiency, MAC prepared from Ceiba pentandra fiber can be used as an effective adsorbent for zinc ion removal from industrial wastewater.

Supramolecular Solvent Extraction-Gas Chromatography-Tandem Mass Spectrometry for Detection of Benzodiazepines in Urines.

Objective To establish a method using supramolecular solvent and gas chromatography-tandem mass spectrometry （GC-MS/MS） to analyze 9 benzodiazepines in urines. Methods Urine samples containing 9 benzodiazepines reference substance were subjected to liquid-liquid extractions with supramolecular solvent, which consisted of tetrahydrofuran and 1-hexanol. The solvent layer was evaporated to dryness by stream of nitrogen. The residue was reconstituted with methanol, and GC-MS/MS analysis was performed on it. The way of data collection was multiple reaction monitoring （MRM） mode; internal standard method was employed for quantification. Results In urine samples, when the range of mass concentration was 1-100 ng/mL for diazepam, midazolam, flunitrazepam and clozapine, 5-100 ng/mL for lorazepam and alprazolam, 2-100 ng/mL for nitrazepam and clonazepam, and 0.2-100 ng/mL for estazolam, respectively, good linearities were obtained, correlation coefficients were 0.999 1-0.999 9, the lower limits of the quantifications ranged from 0.2 to 5 ng/mL, the extraction recovery rates were 81.12%-99.52%. The intra-day precision ［relative standard deviation （RSD）］ and accuracy （bias） were lower than 9.86% and 9.51%, respectively; the inter-day precision （RSD） and accuracy （bias） were lower than 8.74% and 9.98%, respectively. Nine drugs in urine samples showed good stability at ambient temperature and -20 ℃ within 15 days. The mass concentrations of alprazolam in urine samples obtained from 8 volunteers who took alprazolam tablets orally within 8-72 h after ingestions ranged from 6.54 to 88.28 ng/mL. Conclusion The supramolecular solvent extraction GC-MS/MS method for analysis of 9 benzodiazepines in urines provided by this study is simple, fast, accurate and sensitive, which can provide technical support for monitoring of poisoning by benzodiazepines for clinical treatment and judicial identification.

Modeling of destructive interaction of hot jet and solid plate

Based upon the results of a literature review, a set of physical parameters suitable for quantitative comparison in experimental and numerical studies is determined. The review showed the feasibility of modeling the process of the outflow of an immersed jet of inert gas into the surrounding space and the evolution of a free shear layer formed by hot and cold gases to analyze the process of convective and diffusion transport of various types of particles. In the model formulation we consider the problem of solid destruction by a melt of the same substance, as well as by a nitrogen stream at high temperature. The test simulation of the problems of two-phase interaction of a immersed jet of molten liquid and hot gas, on the whole, qualitatively showed the reproduction of the main characteristics of the flow: the generation of large-scale vortices around the jet in the induction zone, the oscillations of the jet when it collides with an obstacle, and the shape of the cavity formed.

Carbon obtained from waste polyethylene terephthalate (PET) containers as potential sorbent of radionuclides from the contaminated aqueous solutions

Waste polyethylene terephthalate (PET) beverage containers have been carbonized in a nitrogen stream and chemically treated to obtain activated carbon. The potential sorbent has been physico-chemically characterized and tested for use in the solidification of liquid radioactive waste (LRW). For this purpose, we have determined main factors describing adsorption of the selected radioactive metals. It was found that adsorption process fulfils Freundlich and kinetic pseudo-second-order models. It has been also shown that activation of the raw PET carbon with using the ZnCl2 solution leads to the best adsorption results of the radionuclides. Activated carbon obtained within this work appeared to be a potential candidate for a low-cost, chemically stable adsorbent for water decontamination. Procedures for the carbonization and activation need, however, to be improved. Activated carbon obtained from waste polyethylene terephthalate (PET) beverage containers appeared to be a potential candidate for a low-cost, chemically stable adsorbent for water decontamination and the management of radioactive liquid wastes (LRW).

Исследование относительной реакционной способности ароматических соединений в воздухе под действием плазмы импульсного разряда

Based on the method of competing reactions, a method for determining the relative reactivity of aromatic vapors in relation to the plasma components of a pulsed corona discharge is developed. The parameters of the relative reactivity of aromatic compounds in the air and nitrogen stream were obtained using model mixtures based on benzene, toluene, and xylene with a content of 250-500 ppm. The effect of water vapor on the process is shown. The obtained data will be useful for optimizing the processes of plasma-chemical air purification from the vapors of toxic aromatic compounds.

Improvement of the procedure for bis(2-chloroethyl)sulfide determination in matrices with high sorption activity

A rapid, unified, highly sensitive and selective procedure for bis(2-chloroethyl)sulfide (sulfur mustard, SM) determination in matrices with high sorption activity using gas chromatography-tandem mass-spectrometry (GC-MS/MS) was developed. Ceramic tile, concrete, various types of bricks and polymers were studied as objects of the analysis. The parameters for the GC-MS/MS determination of SM were optimized. The efficiency of five solvents (diethyl ether, 2-chloropropane, acetonitrile, hexane, and acetone) for the extraction of SM from the various matrices was studied. 2-chloropropane was the extraction solvent of choice. The developed procedure is based on the extraction of SM from the matrix and the concentration of the extract under the stream of nitrogen to 0.2 mL followed by GC-MS/MS analysis. The LODs for SM in all investigated matrices were 0.7-0.9 ng/g (0.007-0.009 MPC). The long-term stability of SM in various materials was studied. It was shown that in brick, concrete and ceramic samples the residual amount of SM after five months of storage at 4°C was below the LOD of the method, while in polymer samples under the same storage condition the amount of SM has not changed significantly. The developed procedure has been applied to the analysis of samples from the former chemical weapons destruction facility.

Comparative evaluation of solid-phase extraction and in-tube liquid-liquid extraction for determination of triazole pesticides in water samples

ABSTRACT In this study, we have compared two extraction methods (in-tube liquid-liquid extraction and solid-phase extraction) in terms of precision, recovery percentage and time. Parameters, influencing the extraction efficiency, such as nature and volume of extraction solvent and pH nature were optimised. Under the optimum conditions, results showed that SPE is certainly more effective than in-tube liquid-liquid extraction. In this method, a volume of the sample solution is acidifed to pH 4.0 and then passed through C18 cartridge, the absorbed analytes are eluted by an appropriate solvent (acetonitrile), the cartridge was centrifuged and finally, the elute was recovered. The extract was evaporated directly with a weak nitrogen stream. The obtained extract was injected into gas chromatography-Mass spectrometry. The results of the validation indicated that this method provided an excellent linearity with correlation coefficients ranged from 0.997 to 0.999; low limits of detection and quantification in the ranges of 0.01–0.04 μg.L−1 and 0.03–0.14 µg.L−1 respectively. Extraction recoveries ranged from 79% to 94%, Enrichment factors in the range of 158–188 and Relative Standard Deviations are less than 3%. At the end, the proposed procedure was successfully applied to the analysis of real samples, the average concentrations of triazole pesticides are 0.51 µg.L−1 and 8.79 µg.L−1. The predominant triazoles founded are Myclobutanil (1.61–8.79 µg.L−1) and Penconazole (0.99–6.89 µg.L−1). Results show that all recorded triazole concentrations exceed the values standardised by the regulations.

Supramolecular solvent (SUPRASs) extraction method for detecting benzodiazepines and zolpidem in human urine and blood using gas chromatography tandem mass spectrometry.

A high-throughput and sensitive method using supramolecular solvent (SUPRASs) for detecting 9 benzodiazepines and zolpidem in human urine and blood by gas chromatography-tandem mass spectrometry (GC-MS/MS) was newly established and applied to authentic human urine and blood samples in this study. Urine and blood samples were subjected to liquid-liquid extractions with supramolecular solvent mixture which consists of tetrahydrofuran and 1-hexanol. The solvent layer was evaporated to dryness by stream of nitrogen. The residue was reconstituted with methanol, and subjected to analysis by GC-MS/MS in multiple reaction monitoring (MRM) mode; internal standard method was employed for quantifying of each targeted compound. The regression equation has a good linear relationship with correlation coefficients for all tested compounds were not lower than 0.9991. The lower limits of the quantification ranged from 0.20 to 5ng/mL for tested compounds in urine; Meanwhile, the lower limits of the quantification in this method ranged from 1 to 50ng/mL for tested compounds in blood. These results showed that excellent reproducibility and satisfactory extraction recovery rates could be obtained for the established analytical method for 10 drugs in both blood and urine samples. The established method in this study was high-throughput, simple and sufficiently sensitive for determining of benzodiazepinesand zolpidem in human urine and blood. Therefore, this newly established method could be of use for qualitative and quantitative determination of such drugs in urine and blood samples either for clinical poisoning monitoring or for forensic identification.

Snowmelt periods as hot moments for soil N dynamics: a case study in Maine, USA.

The vernal transition represents the seasonal transition to spring, occurring as temperatures rise at the end of winter. With rapid snowmelt, microbial community turnover, and accelerated nutrient cycling, this is a critical but relatively under-studied period of ecosystem function. We conducted a study over two consecutive winters (2015-2016) at the Bear Brook Watershed in Maine to examine how changing winter conditions (warming winters, reduced snow accumulation) altered soil nitrogen availability and stream N export during winter and the vernal transition, and how these patterns were influenced by ecosystem N status (N-enriched vs. N-limited). Of the two study years, 2016 had a warmer winter with substantially less snow accumulation and a discontinuous snowpack-and as a result, had a longer vernal transition and a snowpack that thawed before the vernal transition began. Across both years, snowmelt triggered a transition, signaled by increased ammonium concentrations in soil, decreased soil nitrate concentrations due to flushing by meltwater, and increased stream nitrate exports. Despite the contrasting winter conditions, both years showed similar patterns in N availability and export, differing only in the timing of these transitions. The vernal transition has conventionally been considered a critical period for biogeochemical cycling, because the associated snowmelt event triggers physicochemical and biochemical changes in soil systems. This was consistent with our results in 2015, but our data for 2016 show that this may not always hold true, and instead, that warmer, low-snow winters may demonstrate a temporal asynchrony between snowmelt and the vernal transition. We also show that ecosystem N status is a strong driver of the seasonal N pattern, and the interaction of N status and changing climate must be further investigated to understand ecosystem function under our current predicted trajectory of warming winters, declining snowfall, and winter thaw events.

Carbon Nitride Quantum Dots Enhancing the Anodic Electrochemiluminescence of Ruthenium(II) Tris(2,2'-bipyridyl) via Inhibiting the Oxygen Evolution Reaction.

Although electrochemiluminescence (ECL) has been developed significantly in the past few decades, ECL efficiency in aqueous solutions remains quite low. Determination of the energy losses and development of new ECL-enhancing strategies are still of great value. In this work, we discovered a detrimental nonradiation relaxation pathway by a concurrent oxygen evolution reaction (OER) process in a well-known ruthenium(II) tris(2,2'-bipyridyl) (Ru(bpy)32+) aqueous ECL system due to similar surface-sensitive characteristics, and for the first time, a chemical strategy was developed by which carbon nitride quantum dots (CNQDs) could inhibit the surface OER process, alleviate the energy losses by nonradiation relaxation, and enhance the anodic ECL of Ru(bpy)32+. In the Ru(bpy)32+/CNQD system, CNQDs could enhance the anodic ECL of Ru(bpy)32+ in a nitrogen stream (10-fold) and ambient air (161-fold). The luminous and nitrogen-rich CNQDs were also confirmed not to serve as ECL luminophores, anodic coreactants, or donor/acceptors in ECL. The coreactant-free Ru(bpy)32+/CNQD system possesses several advantages over the common coreactant ECL system, such as low dosage (100 μg/mL CNQDs), favorable regeneration capacity, etc. As an example, ECL on-off detection of dopamine utilizing the Ru(bpy)32+/CNQD system was also developed to show prospects in ECL sensing. Besides, CNQDs were introduced into the classical Ru(bpy)32+/C2O42- coreactant ECL system, leading to suppressed OER and improved ECL signal. Overall, the proposed new ECL-enhancing strategy is promising for applicable ECL sensing, could be extended to other ECL luminophores with high oxidation potential, and enables an in-depth understanding of the ECL process and mechanism.

Complete Prevention of Contact Electrification by Molecular Engineering

Summary Electrostatic charges are easily generated on surfaces during contact electrification. Although these invisible charges have emerged as a new dimension in mediating the functions of surfaces, such as energy conversion, liquid transport, reactivity, and adsorbability, the accumulation of charges on surfaces can also pose many undesirable consequences. Despite notable progress, existing approaches in engineering antistatic surfaces suffer from limitations such as the need to modify bulk materials or for delicate control of patterning on surfaces that rely on the neutralization of generated charges. Herein, we report a general toolbox for designing antistatic coatings by leveraging on chemically heterogeneous components with electron-donating and electron-accepting functions, i.e., N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and 1H,1H,2H,2H-perfluorooctyl trimethoxysilane, to molecularly engineer the surface potential to achieve an electrostatic homogeneity and completely prevent charge generation. Our approach is general, which allows the facile fabrication of antistatic coatings on various materials, even flexible and curved, with good re-writability and transparency.