Mixture Of Impurities Research Articles

Bioanalytical evidence that chemicals in tattoo ink can induce adaptive stress responses

Tattooing is becoming increasingly popular, particularly amongst young people. However, tattoo inks contain a complex mixture of chemical impurities that may pose a long-term risk for human health. As a first step towards the risk assessment of these complex mixtures we propose to assess the toxicological hazard potential of tattoo ink chemicals with cell-based bioassays. Targeted modes of toxic action and cellular endpoints included cytotoxicity, genotoxicity and adaptive stress response pathways. The studied tattoo inks, which were extracted with hexane as a proxy for the bioavailable fraction, caused effects in all bioassays, with the red and yellow tattoo inks having the greatest response, particularly inducing genotoxicity and oxidative stress response endpoints. Chemical analysis revealed the presence of polycyclic aromatic hydrocarbons in the tested black tattoo ink at concentrations twice the recommended level. The detected polycyclic aromatic hydrocarbons only explained 0.06% of the oxidative stress response of the black tattoo ink, thus the majority of the effect was caused by unidentified components. The study indicates that currently available tattoo inks contain components that induce adaptive stress response pathways, but to evaluate the risk to human health further work is required to understand the toxicokinetics of tattoo ink chemicals in the body.

Rosetta Images of Comet 67P/Churyumov–Gerasimenko: Inferences from Its Terrain and Structure

The Rosetta mission has given us remarkable images of comet 67P/C-G both from the orbiter, and recently from the Philae lander during its brief days before running out of power. Though its crust is very black, there are several indicators of an underlying icy morphology. Comet 67P displays smooth, planar ‘seas’ (the largest 600 m x 800 m) and flat-bottomed craters, both features seen also on comet Tempel-1. Comet 67P’s surface is peppered with mega-boulders (10-70 km) like comet Hartley-2, while parallel furrowed terrain appears as a new ice feature. The largest sea (‘Cheops’ Sea, 600 x 800 m) curves around one lobe of the 4 km diameter comet, and the crater lakes extending to ~150 m across are re-frozen bodies of water overlain with organic-rich debris (sublimation lag) of order 10 cm. The parallel furrows relate to flexing of the asymmetric and spinning two-lobe body, which generates fractures in an underlying body of ice. The mega-boulders are hypothesised to arise from bolide impacts into ice. In the very low gravity, boulders ejected at a fraction of 1 m/s would readily reach ~100 m from the impact crater and could land perched on elevated surfaces. Where they stand proud, they indicate stronger refrozen terrain or show that the surface they land on (and crush) sublimates more quickly. Outgassing due to ice-sublimation was already evident in September at 3.3AU, with surface temperature peaks of 220-230 K, which implies impure ice mixtures with less strongly-bound H2O. Increasing rates of sublimation as Rosetta follows comet 67P around its 1.3 AU perihelion will further reveal the nature and prevalence of near-surface ices.

Self-consistent theory of a Bose–Einstein condensate with impurity at finite temperature

We study the properties of Bose–Einstein condensate–impurity mixtures at finite temperatures employing the Balian–Vénéroni variational principle. The method leads to a set of coupled nonlinear equations of motion for the condensate and its normal and anomalous fluctuations on the one hand, and for the impurity on the other. We show that the obtained equations satisfy the energy and number conserving laws. Useful analytic expressions for the chemical potential and the radius of both the condensate and anomalous components are derived in the framework of the Thomas–Fermi approximation in a d-dimensional regime. The effects of the impurity on these quantities are discussed.

An experimental overview of the effects of hydrogen impurities on polymer electrolyte membrane fuel cell performance

Hydrogen quality is critical for increasing the reliability, stability, and durability of polymer electrolyte (PEM) fuel cells. In this work, several hydrogen impurities have been studied to understand their effects on PEM fuel cell performance at various operating concentrations. Our studies have shown that the following impurities suggested by industry stakeholders do not result in substantial fuel cell degradation when they are the sole impurity in hydrogen: 5 ppm formaldehyde, 2 ppm formic acid, 19 ppm chloromethane, 30 ppm acetaldehyde, 5% ethylene, 20 ppm toluene, and 10 ppm benzene. In addition, a specific mixture of impurities called the “specification concentration level cocktail” consisting of 0.2 ppm carbon monoxide, 4 ppb hydrogen sulphide, 0.2 ppm formic acid, 2 ppm benzene, and 0.1 ppm ammonia in hydrogen, also does not show significant effects on cell performance. In comparison, when a cocktail having five times the specification concentration is introduced into the cell, significant performance loss is evident.

Alternaria alternata and its allergens: a comprehensive review.

Alternaria alternata is mainly an outdoor fungus whose spores disseminate in warm, dry air, so in temperate climates, their count peaks in the summers. Alternaria may also be found in damp, insufficiently ventilated houses, where its allergenic properties cocreate the sick building syndrome. Mold-induced respiratory allergies and research on Alternaria both have a lengthy history: the first was described as early as 1698 and the second dates back to 1817. However, the two were only linked in 1930 when Alternaria spores were found to cause allergic asthma. The allergenic extracts from Alternaria hyphae and spores still remain in use but are variable and insufficiently standardized as they are often a random mixture of allergenic ingredients and coincidental impurities. In contrast, contemporary biochemistry and molecular biology make it possible to obtain pure allergen molecules. To date, 16 allergens of A. alternata have been isolated, many of which are enzymes: Alt a 4 (disulfide isomerase), Alt a 6 (enolase), Alt a 8 (mannitol dehydrogenase), Alt a 10 (alcohol dehydrogenase), Alt a 13 (glutathione-S-transferase), and Alt a MnSOD (Mn superoxide dismutase). Others have structural and regulatory functions: Alt a 5 and Alt a 12 comprise the structure of large ribosomal subunits and mediate translation, Alt a 3 is a molecular chaperone, Alt a 7 regulates transcription, Alt a NTF2 facilitates protein import into the nucleus, and Alt a TCTP acts like a cytokine. The function of four allergenic proteins, Alt a 1, Alt a 2, Alt a 9, and Alt a 70kDa, remains unknown.

Physico-Chemical Analysis of Waste Water Used for Agricultural Purpose in Surrounding of Hyderabad, Sindh, Pakistan

Irrigation with sewage is common practice of the farmers living in surrounding areas of urban colonies in Pakistan. Sewage contains a complex mixture of impurities. Waste water used for agricultural purpose without any treatment though it contains lot of the harmful impurities. During this study three villages were selected around the Hyderabad city and 12 samples were collected. Various characteristics of the sewage samples were determined such as total residues, total fixed residues, volatile residues, salinity, alkalinity, TDS, temperature, color, pH, conductivity, etc. Aim of this study was to evaluate the quality of waste water. It was found that waste water had moderate to increased hardness and salinity. Moreover, these water samples contained from 300 to 1800 mg/L of total residues. Nevertheless the pH-value was normal, in the range 6.7-7.0, that is suitable for water used for irrigation. Further investigations are required to determine toxicity of the waste water, as well as content and accumulation of heavy metals.

The Effect of Common Airborne Impurities and Mixtures on PEMFC Performance and Durability

This work reports the performance and durability effects resulting from exposing the cathode of a hydrogen proton exchange membrane fuel cell (PEMFC) to air containing benzene (BZ), sulfur dioxide (SO2), and nitrogen dioxide (NO2) at concentrations ≤ 2 ppm for single impurities and in mixtures. This is the first phase of a project to deploy fuel cell powered buses in Hawai‛i Volcanoes National Park (HAVO). The data reported herein is obtained from 50 cm2 single cells and will contribute to the future development of: (i) performance specifications for air filtration media used in fuel cell buses, (ii) a fuel cell stack model that predicts performance when impurities are present, and (iii) operational protocols for the system used to control the PEMFC stack.The impurities investigated in this work have been studied previously as single impurities and shown to have a detrimental impact on fuel cell performance (1-3). Some groups have also investigated impurity mixtures and reported that they can adversely affect performance even at ppm level concentrations (4-6). One group identified a negative correlation between the performance of PEMFC systems and ambient air pollution (6). More information on the performance and durability effects of both single impurities and mixtures is needed at conditions similar to those at which the fuel cell bus will be operating. Additionally, the effectiveness of using clean air to recover performance must be evaluated given the challenging environmental conditions of HAVO.Impurity exposures were performed by injection into the air stream of the PEMFC for a minimum of 20 hours. Impurity concentrations were 2 ppm for single components, 1 and 1 ppm for two components, and 0.67 ppm x 3 for three components. Concentration configurations were chosen to investigate if synergistic effects existed where the performance loss from multi-component mixtures was greater than the loss from equivalent single impurities. The cell was operated at a temperature of 60ºC and constant current densities of 1 and 0.2 A cm-2. Current densities were chosen to represent high and low power operating points. Performance recovery was studied by supplying the cell with clean air for 20 hours and monitoring the change in cell voltage.Fig. 1 shows the cell voltage loss resulting from exposing the fuel cell to impurities at 1 A cm-2. Also shown is the recovery during exposure to clean air. Each contaminant significantly decreased cell voltage either as a single contaminant or in a mixture. Mixtures resulted in greater performance loss than single contaminants alone; indicating that a synergistic effect existed and modeling efforts will have to account for this. Performance loss for BZ and NO2 as single contaminants was completely recovered with clean air and was slightly higher than the performance prior to impurity exposure. SO2 was the most significant impurity because it caused the greatest loss in performance, which could not be completely recovered using clean air. Trends similar to those shown in Fig. 1 were observed at 0.2 A cm-2.To determine the effects of the impurities on the durability of the MEA, diagnostics were performed before and after impurity exposure and included cyclic voltammetry to remove impurities from the catalyst and measure changes in electrochemically active surface area (ECSA). Polarization curves were also performed to quantify changes in cell performance. The results will be reported along with gas chromatography data showing changes in the reactions for selected experiments.Future system development efforts should limit impurity exposure to levels much lower than 2 ppm for all impurities studied in this work and consider designing air filtration media that prevents SO2 from reaching the cathode. ACKNOWLEDGEMENTSThe authors are grateful for funding received from the Office of Naval Research (N00014-11-1-0391) and to the Hawaiian Electric Company for their ongoing support to the operations of the Hawai‛i Sustainable Energy.REFERENCESJ. M. Moore, P.L. Adcock, J. B. Lakeman, and G. O. Mepsted, J. Power Sources, 85, 254 (2000).J. St-Pierre, N. Jia, and R. Rahmani, J. Electrochem. Soc., 155, B315 (2008).Y. Zhai, G. Bender, S. Dorn, M. Angelo, K. Bethune, and R. Rocheleau, Electrochem. Soc. Trans., 16(2), 873 (2008).D. Yang, J. Ma, L. Xu, M. Wu, and H. Wang, Electrochim. Acta, 51, 4039 (2006).F. Jing, M. Hou, W. Shi, J. Fu, H. Yu, P. Ming, and B. Yi, J. Power Sources, 166, 172 (2007).J. Biesdorf, N. Zamel, and T. Kurz, J. Power Sources, 247, 339 (2014).

Self-localized state and solitons in a Bose-Einstein-condensate–impurity mixture at finite temperature

We study the properties of a Bose-Einstein-condensate (BEC)--impurity mixture at finite temperature employing the time-dependent Hartree-Fock Bogoliubov (TDHFB) theory which is a set of coupled nonlinear equations of motion for the condensate and its normal and anomalous fluctuations on the one hand and for impurity on the other. The numerical solutions of these equations in the static quasi-one-dimensional regime show that the thermal cloud and the anomalous density are deformed as happens to the condensate and the impurity becomes less localized at nonzero temperatures. Effects of the BEC fluctuations on the self-trapping state are studied in homogeneous weakly interacting BEC-impurity at low temperature. The self-trapping threshold is also determined in such a system. The formation of solitons in the BEC-impurity mixture at finite temperature is investigated.

Experimental setup for investigation of nanoclusters at cryogenic temperatures by electron spin resonance and optical spectroscopies.

We present the design and performance of an experimental setup for simultaneous electron spin resonance (ESR) and optical studies of nanoclusters with stabilized free radicals at cryogenic temperatures. A gas mixture of impurities and helium after passing through a RF discharge for dissociation of molecules is directed onto the surface of superfluid helium to form the nanoclusters of impurities. A specially designed ESR cavity operated in the TE011 mode allows optical access to the sample. The cavity is incorporated into a homemade insert which is placed inside a variable temperature insert of a Janis (4)He cryostat. The temperature range for sample investigation is 1.25-300 K. A Bruker EPR 300E and Andor 500i optical spectrograph incorporated with a Newton EMCCD camera are used for ESR and optical registration, respectively. The current experimental system makes it possible to study the ESR and optical spectra of impurity-helium condensates simultaneously. The setup allows a broad range of research at low temperatures including optically detected magnetic resonance, studies of chemical processes of the active species produced by photolysis in solid matrices, and investigations of nanoclusters produced by laser ablation in superfluid helium.

High-throughput profiling of protein N-glycosylation by MALDI-TOF-MS employing linkage-specific sialic acid esterification.

Protein glycosylation is an important post-translational modification associated, among others, with diseases and the efficacy of biopharmaceuticals. Matrix-assisted laser desorption/ionization (MALDI) time-of-fight (TOF) mass spectrometry (MS) can be performed to study glycosylation in a high-throughput manner, but is hampered by the instability and ionization bias experienced by sialylated glycan species. Stabilization and neutralization of these sialic acids can be achieved by permethylation or by specific carboxyl group derivatization with the possibility of discrimination between α2,3- and α2,6-linked sialic acids. However, these methods typically require relatively pure glycan samples, show sensitivity to side reactions, and need harsh conditions or long reaction times. We established a rapid, robust and linkage-specific high-throughput method for sialic acid stabilization and MALDI-TOF-MS analysis, to allow direct modification of impure glycan-containing mixtures such as PNGase F-released human plasma N-glycome. Using a combination of carboxylic acid activators in ethanol achieved near-complete ethyl esterification of α2,6-linked sialic acids and lactonization of α2,3-linked variants, in short time using mild conditions. Glycans were recovered by hydrophilic interaction liquid chromatography solid phase extraction and analyzed by MALDI-TOF-MS in reflectron positive mode with 2,5-dihydroxybenzoic acid as the matrix substance. Analysis of the human plasma N-glycome allowed high-throughput detection and relative quantitation of more than 100 distinct N-glycan compositions with varying sialic acid linkages.

Synthesis and purification of iodoaziridines involving quantitative selection of the optimal stationary phase for chromatography.

The highly diastereoselective preparation of cis-N-Ts-iodoaziridines through reaction of diiodomethyllithium with N-Ts aldimines is described. Diiodomethyllithium is prepared by the deprotonation of diiodomethane with LiHMDS, in a THF/diethyl ether mixture, at -78 °C in the dark. These conditions are essential for the stability of the LiCHI2 reagent generated. The subsequent dropwise addition of N-Ts aldimines to the preformed diiodomethyllithium solution affords an amino-diiodide intermediate, which is not isolated. Rapid warming of the reaction mixture to 0 °C promotes cyclization to afford iodoaziridines with exclusive cis-diastereoselectivity. The addition and cyclization stages of the reaction are mediated in one reaction flask by careful temperature control. Due to the sensitivity of the iodoaziridines to purification, assessment of suitable methods of purification is required. A protocol to assess the stability of sensitive compounds to stationary phases for column chromatography is described. This method is suitable to apply to new iodoaziridines, or other potentially sensitive novel compounds. Consequently this method may find application in range of synthetic projects. The procedure involves firstly the assessment of the reaction yield, prior to purification, by (1)H NMR spectroscopy with comparison to an internal standard. Portions of impure product mixture are then exposed to slurries of various stationary phases appropriate for chromatography, in a solvent system suitable as the eluent in flash chromatography. After stirring for 30 min to mimic chromatography, followed by filtering, the samples are analyzed by (1)H NMR spectroscopy. Calculated yields for each stationary phase are then compared to that initially obtained from the crude reaction mixture. The results obtained provide a quantitative assessment of the stability of the compound to the different stationary phases; hence the optimal can be selected. The choice of basic alumina, modified to activity IV, as a suitable stationary phase has allowed isolation of certain iodoaziridines in excellent yield and purity.

Orientational glass in mixtures of elliptic and circular particles: structural heterogeneities, rotational dynamics, and rheology.

Using molecular dynamics simulation with an angle-dependent Lennard-Jones potential, we study orientational glass with quadrupolar symmetry in mixtures of elliptic particles and circular impurities in two dimensions. With a mild aspect ratio (= 1.23) and a mild size ratio (= 1.2), we realize a plastic crystal at relatively high temperature T. With further lowering T, we find a structural phase transition for very small impurity concentration c and pinned disordered orientations for not small c. The ellipses are anchored by the impurities in the planar alignment. With increasing c, the orientation domains composed of isosceles triangles gradually become smaller, resulting in orientational glass with crystal order. In our simulation, the impurity distribution becomes heterogeneous during quenching from liquid, which then produces rotational dynamic heterogeneities. We also examine rheology in orientational glass to predict a shape memory effect and a superelasticity effect, where a large fraction of the strain is due to collective orientation changes.

Biomass Gasifier–SOFC Systems: From Electrode Studies to the Development of Integrated Systems and New Applications

An overview of the research activities and on-going multiple projects at Delft University of Technology aimed at the development of Gasifier–Solid Oxide Fuel Cell (SOFC) based power plants are presented. Biosyngas generated in gasifiers consists of a mixture of carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), hydrogen (H2), nitrogen (N2), water vapor (H2O), and minor impurities. Biosyngas can be a good fuel for SOFCs provided that the gas is sufficiently cleaned. Influence of biosyngas compositions and biomass-derived contaminants on SOFCs is presented and the removal of potential contaminants such as tar, particulates, H2S, HCl, and alkali compounds from biosyngas is discussed. It appears that the gasification product gas can be cleaned to meet the requirements of SOFCs using currently known gas cleaning methods. Additionally, a brief discussion on the achievable system efficiencies with gasifier–SOFC systems is presented. Innovative applications of the gasifier-SOFC systems being developed at Delft, such as advanced gasifier–SOFC systems for toilet development, are also presented.

Evaluation of supercritical fluid chromatography for testing of PEG adducts in pharmaceuticals

Drug formulations containing polyethylene glycol may give rise to formation of reaction products between the aforementioned and the active pharmaceutical ingredient. Supercritical fluid chromatography has recently achieved new interest and improved instrumentation is now available. Here, supercritical fluid chromatography has been evaluated for its possible use for determination of reactions products formed between polyethylene glycol and active pharmaceutical ingredients.A mixture of polyethylene glycols with average molecular weights of 400–6000Da was separated with supercritical fluid chromatography using silica columns and carbon dioxide modified with methanol as mobile phase. Satisfactory resolution (Rs=1.2) of the individual oligomers up to a molecular weight of 1000Da was obtained using evaporative light scattering as detection technique. The active pharmaceutical ingredients, cetirizine or indomethacin were investigated in a reaction mixture containing polyethylene glycol 400 after incubation at 80°C for 120h. Polyethylene glycol esters formed upon reaction with both active pharmaceutical ingredients were observed as polymeric patterns with ultraviolet detection and identified with mass spectrometry. Cetirizine was observed to be more reactive than indomethacin. The observed difference in reactivity is due to differences in polar and steric effects between cetirizine and indomethacin. Evaporative light scattering, ultraviolet absorbance and mass spectrometric detection were investigated and each detection technique has its own advantages and disadvantages, but in order to be able to detect selected impurities in the complex mixture of impurities formed, mass spectrometry is superior.

Dependence of the effective coefficient of separating a mixture of NH3-O2 and NH3-N2 on the rate of distillation

The effective coefficient for separating a mixture of NH3-O2 and NH3-N2 at different rates of distillation is determined experimentally and theoretically. The effect of the temperature of a surface layer of liquid ammonia on the purification process from permanent gases (O2 and N2) is studied. The results indicate that upon an increase in the rate of distillation, the efficiency of separating a mixture of ammonia and impurities rises as heat transfer in the surface layer becomes difficult.

LC-MS and LC-NMR as Complementary Techniques for the Determination of Pharmaceuticals in Dosage Formulations

Pharmaceuticals contain not only pharmacologically active compounds but also a range of excipients. The danger exists that impurities may also be present in such drugs, which may adversely affect their efficacy and even endanger patient health and life. Monitoring the composition of pharmaceutical products is therefore essential. The trace amounts of such impurities in pharmaceuticals are often identified and determined with liquid chromatography coupled with mass spectrometry (LC-MS) or with nuclear magnetic resonance spectroscopy (LC-NMR). With the LC-MS technique, compounds known or suspected to be present in the sample can be identified, but this technique is unsuitable for identifying unknown compounds. In the latter case NMR spectra usually provide reliable structural information; in combination with LC, a mixture of impurities can be identified. The simultaneous use of LC-MS and LC-NMR may supply valuable information on the molecular weight and chemical structure of a compound. This article discusses the merits and shortcomings of both methodologies for determining the structures of unknown compounds. The two approaches should be treated as complementary.

Automated Solid Phase Extraction (SPE) LC/NMR Applied to the Structural Analysis of Extractable Compounds from a Pharmaceutical Packaging Material of Construction

The structural analysis (i.e., identification) of organic chemical entities leached into drug product formulations has traditionally been accomplished with techniques involving the combination of chromatography with mass spectrometry. These include gas chromatography/mass spectrometry (GC/MS) for volatile and semi-volatile compounds, and various forms of liquid chromatography/mass spectrometry (LC/MS or HPLC/MS) for semi-volatile and relatively non-volatile compounds. GC/MS and LC/MS techniques are complementary for structural analysis of leachables and potentially leachable organic compounds produced via laboratory extraction of pharmaceutical container closure/delivery system components and corresponding materials of construction. Both hyphenated analytical techniques possess the separating capability, compound specific detection attributes, and sensitivity required to effectively analyze complex mixtures of trace level organic compounds. However, hyphenated techniques based on mass spectrometry are limited by the inability to determine complete bond connectivity, the inability to distinguish between many types of structural isomers, and the inability to unambiguously determine aromatic substitution patterns. Nuclear magnetic resonance spectroscopy (NMR) does not have these limitations; hence it can serve as a complement to mass spectrometry. However, NMR technology is inherently insensitive and its ability to interface with chromatography has been historically challenging. This article describes the application of NMR coupled with liquid chromatography and automated solid phase extraction (SPE-LC/NMR) to the structural analysis of extractable organic compounds from a pharmaceutical packaging material of construction. The SPE-LC/NMR technology combined with micro-cryoprobe technology afforded the sensitivity and sample mass required for full structure elucidation. Optimization of the SPE-LC/NMR analytical method was achieved using a series of model compounds representing the chemical diversity of extractables. This study demonstrates the complementary nature of SPE-LC/NMR with LC/MS for this particular pharmaceutical application. The identification of impurities leached into drugs from the components and materials associated with pharmaceutical containers, packaging components, and materials has historically been done using laboratory techniques based on the combination of chromatography with mass spectrometry. Such analytical techniques are widely recognized as having the selectivity and sensitivity required to separate the complex mixtures of impurities often encountered in such identification studies, including both the identification of leachable impurities as well as potential leachable impurities produced by laboratory extraction of packaging components and materials. However, while mass spectrometry-based analytical techniques have limitations for this application, newer analytical techniques based on the combination of chromatography with nuclear magnetic resonance spectroscopy provide an added dimension of structural definition. This article describes the development, optimization, and application of an analytical technique based on the combination of chromatography and nuclear magnetic resonance spectroscopy to the identification of potential leachable impurities from a pharmaceutical packaging material. The complementary nature of the analytical techniques for this particular pharmaceutical application is demonstrated.

Blistering and re-deposition on tungsten exposed to ASDEX Upgrade divertor plasma

A well-polished and pre-characterised polycrystalline tungsten specimen was exposed to the outer divertor plasma of ASDEX Upgrade close to the strike point for 510 discharges in the campaign 2011 by using the divertor manipulator system. The exposure with a mixture of hydrogen and various impurities leads to blistering. The exposure parameters are comparable to those used in blistering studies under laboratory conditions. Furthermore, spherical dust particles formed by the strong plasma contact were transported and deposited onto the nearly vertically orientated target plates, i.e., the analysed specimen. In subsequent discharges, these particles were partly eroded and a microscopic pattern of layered deposits was formed around them with an elongation rotated ∼40° to the projected B field line direction.

Eosin Y-sensitized graphitic carbon nitride fabricated by heating urea for visible light photocatalytic hydrogen evolution: the effect of the pyrolysis temperature of urea

Graphitic carbon nitride (g-C3N4) was prepared by pyrolysis of urea at different temperatures (450-650 °C), and characterized by thermogravimetric and differential thermal analysis (TG-DTA), elemental analysis (C/H/N), X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), Brunauer-Emmett-Teller (BET) analysis, Fourier transform-infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The samples prepared at low temperatures (450 and 500 °C) are a mixture of g-C3N4 and impurities, whereas the samples prepared at high temperatures (550, 600 and 650 °C) should be g-C3N4 (polymeric carbon nitride). The polymerization degree of g-C3N4 for the prepared samples increases to a maximum at 600 °C with increasing pyrolysis temperature and then decreases, whereas the defect concentration changes conversely, that is, g-C3N4 prepared at 600 °C has the lowest defect concentration. Using Eosin Y (EY) and the prepared sample as the sensitizer and the matrix, respectively, the photocatalytic activity for hydrogen evolution from aqueous triethanolamine solution was investigated. The g-C3N4 prepared at 600 °C exhibits the highest sensitization activity. Under optimum conditions (1.25 × 10(-5) mol L(-1) EY and 7.0 wt% Pt), the maximal apparent quantum yield of EY-sensitized g-C3N4 prepared at 600 °C for hydrogen evolution is 18.8%. The highest activity can be attributed to the pure composition, the higher dye adsorption amount and the lowest defect concentration.

Application of two‐dimensional selective‐TOCSY HMBC for structure elucidation of impurities in mixture without separation

In the pharmaceutical industry, regulatory expectations driven by patient safety considerations make structure elucidation of impurities at levels greater than 0.1% in the active pharmaceutical ingredient (API) of primary interest. Impurities can be generated from isomers in starting materials, or produced from different process steps toward the final API. Proton peaks belonging to different impurities could be potentially identified in the one-dimensional (1)H NMR spectrum, when evaluated in combination with two-dimensional (2-D) COSY and HSQC data. However, in 2-D HMBC data, correlation responses from different impurities may overlap with those from the major component, causing uncertainty of long-range proton to carbon correlations and quaternary carbon assignments. This observation prompts us to design the 2-D selective-TOCSY HMBC experiment to distinguish responses from different impurities in mixtures to obtain 2-D NMR data for each impurity, thus eliminating the use of a chromatographic isolation step to obtain material for NMR analysis. This methodology is demonstrated for structure elucidation of impurities ranging from 8.2% in the raw material to 0.4% in the API in this study, and would be particularly useful for industrial samples in which the solubility and availability of material are not an issue.