Main Impurities Research Articles

Approaching the radiating X-point in SOLPS-ITER modeling of ASDEX Upgrade H-mode discharges

In the present paper the ASDEX Upgrade (AUG) experimental trend of reaching the radiating X-point with nitrogen seeding is reproduced by SOLPS-ITER code modeling. In these experiments the whole divertor region below the X-point is cooled down by the impurity radiation if the seeding rate is large enough, and the maximal radiation is registered from the X-point region, or even from the confinement zone above the X-point. It is demonstrated that for constant seeding rate SOLPS-ITER simulations of the intensively seeded AUG discharges result in that the confined plasma goes into the radiation collapse as a certain threshold in seeding rate is exceeded. This threshold value increases with increasing discharge power. No stable regimes with the electron temperature below 5 eV in the confinement zone even above the X-point are achieved in the modeling if the seeding rate is large enough, in contrast to the experiment. However, such a regime may be achieved if the fueling, seeding and pumping rates are changing in time. Since the SOLPS-ITER code can simulate only steady state, another modeling strategy is chosen. The fueling and seeding rates are artificially reduced by 3 orders of magnitude and the impurity content is set to satisfy the condition that the ratio of electrons contribution originating from fuel atoms to ones coming from impurity atoms is about unity. It is suggested that the radial width of the cooled region in the confinement zone is of the order of the scrape-off layer width λ q , since it is driven by the same physics leading the energy flux to go from mostly radial to mostly parallel. Under these conditions, the radiative spot above the X-point behaves as the energy sink similarly to the energy sink near the divertor in the conventional regime. In extreme regimes (with large seeding rate), the width of the cold region inside the separatrix may exceed λ q , and up to 90% of discharge power can be radiated from the confined region. An estimate of the poloidal length of the radiative spot is suggested as well. Flow patterns of neutrals, deuterium ions, impurities, electric current and heat flows are analyzed for the regimes with intensive X-point radiation. The formation of an electric potential peak above the X-point is observed in the simulations, and the corresponding E × B drift flux appears to give the largest contribution to the main ion and impurity fluxes. This E × B drift flux together with the large ionization source change the parallel velocity with respect to its neoclassical profile. Consequently, the radial E field deviates from the neoclassical one, which might improve the turbulence suppression.

A facile ionic liquid and p-toluenesulfonic acid pretreatment of herb residues: Enzymatic hydrolysis and lignin valorization

This study aimed to develop a promising biorefinery technology for the value-added utilization of herb residues by using ionic liquid (IL) assisted by aromatic acid (p-toluenesulfonic acid, TsOH) pretreatment. The result showed that the addition of low concentration of TsOH into IL could effectively deconstruct the recalcitrant intercellular structure of herb residues and rapidly extract the lignin fraction. Under the optimum conditions (79% IL, 1.0% TsOH, and 20% H2O at 130 °C and 2 h), the highest cellulose recovery yield of 96.4%, the lignin removal rate of 79.9% and ideal saccharification yield of 98.9% were achieved. Moreover, the main byproduct lignin exhibited comparable yield, high purity, and thermal stability, suggesting the potential application in the conversion of bio-based chemicals and materials. Furthermore, the IL was successfully recycled three times and the recovery rate was at least 95% each time. High saccharification yields and lignin recovery were maintained during all cycles. The hemicellulose-derived saccharides were the main impurities detected in the recycled IL. Overall, this work presents a novel green pretreatment process that can effectively utilize herb residues.

Forced degradation study and characterization of main impurities of ibuprofen soft gelatin capsules by LC-MS-QTOF.

Ibuprofen soft gelatin capsules were subjected to degradation under acidic, basic, oxidation, photolytic, thermal, humidity, and metal ions conditions. To analyse the degradation products, a reversed-phase liquid chromatography (RP-LC) indicative stability method was successfully developed. Chromatographic separation was achieved using a Poroshell HPH-C18 150 x 4.6 mm, 4 μm, column at 25 °C, with a mobile phase constituted by 0.1% phosphoric acid and acetonitrile in gradient at a flow rate of 1.0 mL• min -1 , using ultraviolet detection at 220 nm and injection volume of 20 μL. In total, eight unknown impurities were found. The peaks RRt 0.49, RRt 0.75, and RRt 0.95 were above 0.17%, corresponding to the identification threshold. Those were identified and characterized by LC-MS-QTOF, with the same chromatographic conditions, except for the exchange of 0.1% phosphoric acid for 0.1% formic acid. The impurities originated from the interaction of ibuprofen with excipients: esterification with PEG, with sorbitol/sorbitan, and with glycerol by-products, which has not yet been reported in the literature. The developed method can be used in several pharmaceutical areas as quality control of impurities, studies of forced degradation, and for the development of future formulations.

Selective and sensitive colorimetric detection of p-aminophenol in human urine and paracetamol drugs based on seed-mediated growth of silver nanoparticles

p -aminophenol ( p AP), which is a well-known nephrotoxicant, has been widely used in diverse industries as a versatile intermediate material for the synthesis of chemical products. The concentration of p AP in urine is one of the markers for exposure assessment of carcinogenic aniline compounds, and p AP is also the main impurity in paracetamol-based pain-relieving drugs. Herein, we developed a colorimetric sensor for selective and sensitive assay of p AP in human urine and paracetamol drugs. Silver nanoparticles were used as a colorimetric indicator that changes color upon its growth because of the reducing power of p AP. The developed p AP sensor provides a dynamic linear range of 0–85 μ M with a low limit of detection of 0.32 μ M through an ultraviolet (UV)–visible (Vis) spectrometer. A clear color change was observed at 15 μ M, making the proposed colorimetric sensor suitable for a point-of-care diagnosis by naked eyes. Our p AP assay is highly accurate for the standard addition method for both urine and paracetamol samples, with a recovery rate above 94%, proving the feasibility of using the sensor in daily applications. • We developed a selective and sensitive colorimetric sensor for p-aminophenol ( p AP). • The colorimetric p AP sensor has a dynamic linear range 0–85 μ M & LOD of 0.32 μ M. • Convenient visual inspection is available at 15 μ M concentration of p AP. • The developed sensor can efficiently detect p AP in human urine and paracetamol drug.

Innovative green approach for the selective extraction of high-purity selenium from hazardous selenium sludge

Hazardous selenium sludge is a critical intermediate byproduct of the comprehensive recovery of selenium from copper anode slime, and the sustainable extraction of Se is an important basis for the development of high-tech Se-containing materials. Unfortunately, current processes are constrained by complex procedures, serious pollution, ineffectiveness and difficulty in separating Se-Te. This study has developed an innovative green approach utilizing the phase transformations of impurities combined with vacuum distillation to efficiently extract high-purity selenium from selenium sludge and to overcome these issues. The main impurities of Te, Cu, and Pb exist as elemental Te, PbTe, TeO, Cu2Se, and PbSe, and a green oxidizing reagent (H2O2) is employed to convert these impurities into low volatile TeO, CuSeO3, and PbSeO3. Then, high-purity selenium (Se 99.998%) is extracted by vacuum distillation. The appropriate dose of H2O2 is 15 ml per 100 g of sludge at 300 rpm, 0.5 h, and room temperature. Furthermore, the optimal vacuum distillation conditions are 733 K, 1 h, and 1–10 Pa. After completing the whole process, the total yield of high-purity selenium reaches 87.86%. This study provides an efficient and environmentally friendly process to dispose of hazardous selenium sludge and extract high-purity selenium for further use, which has important industrial applications.

Effect of Carbonate on Desilication of Sodium Aluminate Solution at High Temperature

Carbonate is the main anionic impurity in alumina produced by the Bayer process. The phase composition, morphology, and precipitation activity of desilication products (DSPs) precipitated at 245°C in sodium aluminate solution with different carbonate concentrations have been investigated by x-ray diffraction (XRD) and scanning electron microscopy–energy-dispersive x-ray spectroscopy (SEM–EDS) methods. The crystalline DSPs without carbonate are composed of zeolite, sodalite, and hydroxy-sodalite, but only zeolite and cancrinite precipitate in the presence of carbonate. Increasing the carbonate concentration promotes the precipitation of cancrinite but reduces the crystallinity of various DSPs. The cell parameters and the Na2O/Al2O3 ratios of DSPs are significantly increased because of the entry of sodium carbonate during crystallization, especially for the cancrinite. The morphology of various DSPs is greatly changed by the carbonate. The amorphous phase content and precipitation activity of DSPs increase with increasing carbonate concentration. This contributes to the effective removal of carbonate from sodium aluminate solution by controlling the desilication process.

Chemical reactions during iron reduction from oxides with hydrogen

Hydrogen is mainly used in the reduction annealing of iron powder obtained by spraying liquid metal by water. The chemical aspects of this process were modeled using the TERRA 6.3 software package. In particular, the Fe – O – H thermodynamic system has been analyzed in a wide range of temperatures and hydrogen consumption. The analysis has shown that the main impurity compounds of the sprayed powder will not be iron hydrates, but Fe 2 O 3 oxide. But it cannot exist in the atmosphere of hydrogen and is converted to Fe 3 O 4 oxide at a low temperature. Therefore, the main reaction for iron reduction will be Fe 3 O 4 + 4H 2 = 3Fe + 4H 2 O, which ends at 910 °C. It is shown that this reaction temperature can be significantly reduced with an equally significant increase in hydrogen consumption. Taking this factor into account can be useful when working out the powder annealing mode.

Separation of Al-Si-Fe-(Mn/Cr) melts for simultaneous recycle of Al-Si scraps and purification of silicon

Currently, the elimination of Fe from Al-Si alloy for recycling Al-Si scraps, and the purification of Si using Al-Si solvent for recycling Si wafers in solar cells or production of new Si wafers, are two totally different research technologies and topics. A new approach is proposed in this study to combine the two different technologies into a single one which can not only recycle spent Si wafers but also Al-Si scrap simultaneously. The new approach is promising for cost reduction and environmental conservation, because two widely used products, high-purity Si and low Fe eutectic Al-Si alloys, can be prepared simultaneously via electromagnetic directional crystallization. The Al-Si-Fe-(Mn/Cr) melt was separated into a low-Fe eutectic Al-Si alloy (eutectic Al-Si-Fe-(Mn/Cr) alloy) and agglomerated high-purity Si crystals. The critical concentration of Fe (theoretical minimum value of Fe content) in the eutectic Al-Si-Fe-(Mn/Cr) alloys were determined experimentally for the first time, which decreased and increased slightly after the addition of Mn and Cr, respectively. After removing Fe, the residual Fe-containing impurities in the low-Fe eutectic Al-Si-Fe-(Mn/Cr) alloy were modified from their harmful needle-like shape to less harmful Chinese-script-like, and short platelet-like shapes by adding small amounts of Mn and Cr, respectively. After grinding the agglomerated Si crystals and leaching the main impurities, namely Mn, B, Cr , Ca, Al, P, Fe, and Ni, from the Si powders, the purity of Si was upgraded from 99.34% to 99.96%. This new and promising approach can be used for the purifying Si, recycling Si wafers and Al-Si scraps.

Cyclotron-based rhenium-186 production using proton beam of up to 50 MeV

Rhenium-186 (186Re) radioisotope has been suggested for palliative radiotherapy of bone metastic cancer patients and radiosynovectomy in nuclear medicine. Currently 186Re has been mostly produced using neutron activation in nuclear reactors, whereas cyclotron-based production has not been well explored. In this paper, we theoretically propose cyclotron-based proton beams of up to 50 MeV for 186Re production. By Employing the TALYS 2017 codes, we calculated nuclear cross-section for (p, n) nuclear reaction and then buit Matlab codes for the End-of-Bombardment (EOB) yield calculations of 186W(p, n)186Re nuclear reaction while the predicted impurities were calculated for (p, 2n), (p, np), (p,α) and (p, d) nuclear reactions respectively. The TALYS calculated cross-sections indicated that the threshold energy for 186W(p, n)186Re nuclear reaction is 8 MeV. The maximum calculated EOB yield for 186W(p, n)186Re reaction at 50 MeV was 93.64 kBq/µAh which agreed with experimental data published elsewhere. The threshold energies for the (p,2n), (p, np), (p,α) and (p, d) were 7.58, 7.23, 2.0 and 4.99 MeV respectively. In addition, two radionuclides, i.e. 185W and 183mRe as well as two stable isotopes, i.e. 185Re and 184W were predicted to be the main impurities in the 186Re production. This study can be used as a reference for future 186Re production when proton beams of up to 50 MeV are employed.

Calculated cyclotron-based scandium-47 production yields via 48Ca(p, 2n)47Sc nuclear reaction

Scandium-47 is a promising particle emitter that has been suggested as a candidate for radiotheranostics. Thus, better understanding of optimum irradiation parameters, radioactivity yields and possible impurities during its production is of paramount importance. The theoretical calculation of the end-of-bombardment (EOB) results is performed using Microsoft Excel following the calculation of the excitation function obtained from the TALYS software and the stopping power obtained from the SRIM software can be accessed for free. According to the TALYS code calculations, the threshold energy for 47Sc production was 8.39 MeV, whereas the maximum cross-section (879 mbarn) occurred at proton incident energy of 17 MeV. The calculated EOB yield for 48Ca(p,2n)47Sc nuclear reaction at 60 MeV proton energy was found to be 449 MBq/μAh, which was suitable quality for typical radionuclide production. Besides, three radionuclides, i.e. 48Sc, 46Sc and 47Ca were predicted to be the main impurities in the 47Sc production. However, in order to minimize the production of 48Sc, 46Sc and 47Ca impurities radionuclide the safest and optimum proton energy should be between 23 and 30 MeV, which can be achieved using the available 26 MeV cyclotron. This study can be used as a reference for future 47Sc production when proton beams of up to 60 MeV are employed.

Molten chloride salts for high-temperature thermal energy storage: Continuous electrolytic salt purification with two Mg-electrodes and alternating voltage for corrosion control

Molten chloride salts such as MgCl2/KCl/NaCl are promising thermal energy storage (TES) materials and heat transfer fluids (HTF) in next generation concentrated solar power (CSP) plants with elevated operation temperatures (>700 °C) due to their high thermal stability and low material costs. However, they have strong corrosivity against metallic structural materials at high temperatures which can be related to the presence of hydrolysis products such as MgOHCl. In an electrolytic purification method reported in previous work, a W-cathode and Mg-anode were used to reduce the concentration of these impurities, thereby effectively purifying the molten MgCl2/KCl/NaCl salt. However, the W-cathode passivation due to production of MgO on the surface limited its cathode effectiveness. In this work, an improved electrolytic purification method is presented to avoid the electrode passivation by using two identical Mg-electrodes and alternating voltage (AV, i.e., switching the voltage direction applied periodically). A continuous electrolytic salt purification in the AV-mode is successfully performed on the molten MgCl2/KCl/NaCl salt in the 100 g-scale. Cyclic voltammetry (CV) on the molten salt shows that the purification can effectively reduce the concentration of the main corrosive impurity MgOH+Cl−. Potentiodynamic polarization (PDP) measurements on a commercial alloy (Incoloy 800 H) immersed in the molten salt indicate significantly reduced corrosion rates (i.e., reduced salt corrosivity) compared to a non-purified salt. The continuity of the improved method allows for a long-term effective purification without the risk of passivation and deactivation of electrodes, thereby showing great potential in corrosion control of molten chloride salt TES system.

ДОСЛІДЖЕННЯ ВАЛІДАЦІЙНИХ ХАРАКТЕРИСТИК МЕТОДИКИ КІЛЬКІСНОГО ВИЗНАЧЕННЯ ПАРАЦЕТАМОЛУ ТА ЙОГО ОСНОВНОЇ ДОМІШКИ В РЕКТАЛЬНИХ СУПОЗИТОРІЯХ

Еxploration of validation characteristicsof the method for the quantitative determination of paracetamol and its main impurity 4-aminophenol in rectal suppositories by spectrophotometry (UV) and high performance liquid chromatography (HPLC). Spectrophotometric measurements were carried out on a UV VIS Lambda 35 spectrophotometer (Perkin Elmer, USA) in cuvettes l = 1 cm. We used a Waters 2695 liquid chromatography with a Waters 2489 UV-detector, as well as a Nucleosil C18 chromatographic column with a size of 250 × 4.6 mm, filled with octadecylsilyl sorbent with a particle size of 10 microns. We used reagents: purified water, which was obtained from the Milli Q plant, manufactured by Millipore Corporation (Germany), sodium hydroxide Sigma-Aldrich, cat. № 06203, sodium 1-butanesulfonate Sigma-Aldrich, cat. № 19022-10G-F; ethanol 96%, methanol Sigma-Aldrich (purity 99.9%), formic acid Sigma-Aldrich, cat. № 33015. Validation characteristics were confirmed as specificity, correctness, precision. The total predicted uncertainty of the analytical method for quantitative determination and the limit of quantitative determination of the main impurity of paracetamol, at which the signal-to-noise ratio is fulfilled, is 10% of the initial concentration of the reference solution (0.5 μg / ml). Confirmed linearity for quantitative determination of paracetamol content in the range of 80 to 120% of the nominal value. Statistical processing of experimental data was carried out; the correlation coefficient of the linear dependence (r) between the entered and found values for the quantitative determination of paracetamol is > 0.990, which indicates the correctness of the method. Methods for the quantitative determination of paracetamol and its main impurity in suppositories have been developed and validated. The method for quantitative determination of paracetamol in suppositories is significantly simpler for routine control of a batch of drugs and is cost-effective compared to the HPLC method. The obtained experimental results indicate that according to the studied validation characteristics, the technique is correct and can be reproduced in other laboratories.

ЛЕЖАЛЫЕ ЗОЛОТОНОСНЫЕ ХВОСТЫ КОМБИНАТА «БАЛЕЙЗОЛОТО»: ПРОБЛЕМА УТИЛИЗАЦИИ

The relevance of the research is the need to recultivate the waste from the enrichment of gold-bearing ores that lie in the immediate vicinity of the residential areas of Baley city, which have a negative impact on the environmental situation in it, as well as to develop a technological approach to the extraction of gold and silver. The purpose of the study is to study the material composition and develop a technology for extracting precious metals. The object of the study is the stale tailings of the ZIF-1 plant “Baleizoloto”. The subject of the study is mineral composition of stale tailings, content of useful components and their extraction technology, the method and methodology presented by mineralogical and chemical analyses of enrichment tailings. Results. The analysis of the tailings dumps’ state of the gold recovery factories of the Baleizoloto plant was carried out. The contents of gold and other chemical elements, among which arsenic, zinc, copper, antimony, and lead predominate, were determined. The gold content prevails in the stale tailings of the ZIF-1 factory, which processed the ores of the Baley deposit, and is in the range of 1.09-1.37 g / t, on average – 1.17 g/t. This determines the prospects for their primary processing. The gold in the clay-sand fraction of the stale tailings is mainly found in thin accretions with quartz, carbonates, pyrite, arsenopyrite, sulfosols, and tellurides. The field of application is processing of technogenic raw materials. Conclusions. It was determined that the sizes of gold inclusions are in the range of 0.7-0.03 mm, the gold penetration varies from 63 to 91.15, and on average is 82.13; the main impurity in gold is silver with a content of 8.85-37%; the average silver content in the tailings of the ZIF-1 factory is 1.85 g/t; the recommended technological scheme for processing stale tailings of ZIF-1 of the Baleizoloto plant has been developed, including the following operations: photoelectron-activation preparation, pelletizing with active solution, heap leaching, two-stage sorption with bubbling with ozone

Assessment and regulation of the urbanized territory atmospheric air condition of the Karaganda city of the Republic of Kazakhstan

The work is devoted to the assessment of the atmospheric air on urbanized territories of Karaganda. This work determines the content of 11 pollutants. Measurements were carried out at 14 route posts with the maximum coverage of the entire city territory in June and January in order to obtain seasonal dynamics of atmospheric air pollution. As a result of measurements in July, the maximum single-time content of carbon monoxide, phenol, formaldehyde, hydrogen sulfide, and methyl mercaptans was recorded. In January, carbon monoxide predominates in the city’s air from pollutants, and increased concentrations of hydrogen sulfide are also observed in most parts of the city. Based on the results obtained, the atmospheric pollution index was calculated for 5 substances. Measurements of the pollutants were carried out at different times of the day. It was found, that contamination in almost all analyzed substances is higher in the daytime and in the evening. The main harmful impurities in the air of Karaganda are ozone, carbon monoxide, hydrogen sulfide, phenol, formaldehyde and methyl mercaptans. Ammonia was detected periodically. Based on the results the suggestions for improvement of the atmospheric air condition in the research territory were developed and adopted.

The process of evaporation of sodium sulfate solution by leaching natural raw materials

A specific feature of the chemical composition of the natural mirabilite of the Tumryuk deposit is that the average content of impurity salts of halite, gypsum and epsomite in it is not considered very high. The quality of the product in terms of the content of the main substance and impurity of sodium chloride according to GOST (Government standart) 6318 corresponds to the first grade, and in terms of the amount of impurity of ions MgA(2+)~ to the second grade. The highest demands on the quality of sodium sulfate are imposed by the synthetic detergent industry. This is due to the fact that the micro components introduced into them, which dramatically improve the quality of synthetic detergents, are very sensitive to impurities of some divalent metals, in particular iron, calcium, and zinc.

Impurity Profiling and Identification of 2,6-Diisopropylphenol by HPLC Method and Raman Spectroscopy Method.

Identification of 2,6-diisopropylphenol by Raman spectroscopy using the TruScan Raman spectrum is validated by specificity test and robustness. HPLC assay method is developed to detect the 2,6-diisopropylphenol and its impurities A =determination of 2,6-diisopropylphenol; its main impurities related compound A =2,6-diisopropylphenyl isopropyl ether, related compound B=2,6-diisopropylquinone, and related compound C=3,3'-5,5'-tetraisopropyl diphenol; and unknown impurities done by HPLC method. Related compound A and C determination has been developed by normal phase HPLC; good resolution peak shapes have resulted from the peak results. The limit of impurities A and C is reported to be 0.05% and 0.03%, and the limit of impurity B is also detected by using the same above procedure, but the column has been changed for the maximum wavelength detection and better elution from the peak results. The reported impurity level was 0.02%, the unknown impurity limit was 0.0149%, and the total impurity level of 2,6-diisopropylphenol was reported to be 0.06% which are in the threshold limit level. It specifies that the drug is safe and efficient without any toxicity.

Connecting gasification with syngas fermentation: Comparison of the performance of lignin and beech wood

The integration of gasification with syngas fermentation is still in an early stage of development, where many questions exist concerning the syngas quality required. The challenge is to define the gasification conditions that will provide a H2:CO:CO2 ratio suitable for syngas fermentation, as well as to identify and remove the compounds that can inhibit the performance of the microorganisms. The right balance between the gasification conditions and a line up with minimal gas cleaning needs to be assessed to improve the economic feasibility of the process. In this work a first attempt to combine the two processes is presented, with the aim to provide an insight of the indirect gasification, the gas cleaning applied, the effect of the main impurities and the performance of syngas fermentation. A lignin rich feedstock was gasified with steam in an indirect gasifier, at TNO (Netherlands Organization for Applied Scientific Research). The gas, after removal of some components that could hinder the performance of the fermentation (tar compounds, BTX, unsaturated hydrocarbons and sulphur compounds), consisted of CO, H2, CO2, CH4, C2H6 and traces of other hydrocarbons. The influence of the obtained syngas quality and composition was evaluated in the fermentation process using Clostridium ljungdahlii, at KIT (Karlsruhe Institute of Technology). For comparison, product gas from beech wood gasification was also evaluated in the fermentation process under the same conditions.

Influence of iron, aluminum, calcium, titanium and vanadium impurities removal from silicon based on Cu-catalyzed chemical leaching

In this work, silicon purifying process based on the novel Cu-catalyzed chemical leaching (CuCCL) treatment has been investigated as a function of different silicon particle size, HF concentration, leaching time, H2O2 concentration, Cu(NO3)2 concentration and leaching temperature. Typical impurity precipitate in silicon was analyzed, which revealed that the main impurities of Fe, Al, Ca, Ti, and V mainly exist as Si2Fe, Si–Fe–Al, Si–Fe–Al–Ca, and Si–Fe–Al–Ti–V phases in the MG-Si feedstock. The results showed that the main impurities Fe, Al, Ca, Ti, and V can be effectively eliminated by the CuCCL treatment, especially for Ca, Ti and V. In the appropriate experiment conditions, the removal of main impurities Fe, Al, Ca, Ti, and V from MG-Si significantly reached to 99.38%, 98.64, 100%, 100%, and 100%, respectively. It was found that the impurities on the silicon facilitated the formation of porous structures during the CuCCL process, and the generated porous structures further exposed more impurities to the acid etchants, which promote the impurity removal from silicon. Furthermore, the leaching behaviors of impurity precipitates in the CuCCL process were obtained through revealing their evolution during deposition and etching steps. The high-efficient silicon purification effect of this study may bring some new strategy for achieving the low-cost solar grade silicon.

The chromatographic behaviour of new double-labelled oligodeoxynucleotide probes containing azaphthalocyanine dye as a quencher with respect to evaluation of their purity.

The influence of experimental conditions on chromatographic behaviour of promising oligodeoxynucleotide double-labelled molecular probes containing an azaphthalocyanine macrocycle as a perspective dark quencher was studied. A recently introduced new stationary phase based on styrene-divinylbenzene copolymer was tested. The planar and hydrophobic structure of the azaphthalocyanine is considerably different from those of currently used fluorophores and quenchers. Thus, the most challenging issue was the separation of the double-labelled probe from its main impurity represented by a mono-labelled probe, containing only the azaphthalocyanine macrocycle. The absorbance measurement cannot simply determine this impurity, and its presence fundamentally compromises the biological assay. The commonly used gradient elution was not suitable and isocratic conditions seemed to be more appropriate. The azaphthalocyanine moiety influences the properties of the modified oligodeoxynucleotides substantially, and thus their chromatographic behaviour was determined predominantly by this quencher. Acetonitrile was the preferred organic solvent for the analysis of probes containing the azaphthalocyanine quencher and the effect of ion-pairing reagents was dependent on the probe structure. The temperature seemed to be an effective parameter for fine-tuning of the separation and mass transfer improvement. Generally, our findings could be helpful in method development for purity evaluation of double-labelled oligodeoxynucleotide probes and semipreparative methods.

Understanding the molecular-pharmaceutical basis of sartan recalls focusing on valsartan.

Angiotensin receptor blockers (ARBs) or the ‘sartans’ are widely used for the management of hypertension and heart failure. There have been a series of recent incidents where drug formulations containing different ARBs as active pharmaceutical ingredients have been recalled by various pharmaceutical firms. This article addresses valsartan as well as other sartan recalls besides discussing the recent recalls of ranitidine and metformin, giving insights into the molecular-pharmaceutical basis of the recalls. A thorough literature search of PubMed/Medline and Google Scholar databases was performed to identify all relevant articles and information published up to 29th April 2020 using Medical Subject Headings (MeSH terms) and Boolean operators. We also searched for relevant information on the web using web-browsers and reference lists from original research papers and review articles. The main impurity found was N-nitrosodimethylamine (NDMA) which was thought to be formed due to a change in the manufacturing process of valsartan. Besides, other impurities such N-nitrosodiethylamine (NDEA) and N-nitroso-N-methyl-4-aminobutyric acid (NMBA) were found in batches of other sartans, such as losartan and irbesartan. All of these are carcinogens and harmful if consumed at a level beyond a certain acceptable daily limit. Ranitidine, and more recent metformin recalls, have also been linked with valsartan in view of the presence of NDMA, the same impurity. Safety of ARBs is a major concern among healthcare professionals after the recalls of valsartan in the recent years. Periodic quality assessment of the manufacturing process and the drugs is key to ensure safe, effective and high-quality drugs for the global population. Additionally, practising physicians need to be vigilant in reporting adverse events in their patients receiving treatments.