Water-soluble Impurities Research Articles

Resource treatment of coking sulfur paste: Characterization analysis and composition of impurities

Coking sulfur paste (CSP) generated from coking oven gas desulfurization process is an extremely harmful pollutant. In this article, modern analytic methods, such as X‐ray fluorescence, X‐ray diffraction, Fourier transform infrared, thermo gravimetric‐differential scanning calorimetry and scanning electron microscope, were utilized to analyze CSP. Results showed that sulfur in CSP mainly existed in the form of elemental sulfur, which is presented mostly in the form of rhombic sulfur (Sα). The rest of sulfur existed in the form of NH4SCN, (NH4)2S2O3, FeSO4. There were also microelements in CSP, such as Fe, Br, Ca, P, Mo and Cl, whose contents were less than 2.50%. Impurities in CSP could be divided into three categories: water‐soluble impurities (WI), dichloromethane‐soluble impurities (DI) and other impurities (OI), accounting for 4.2%, 12.16% and 2.61%, respectively, among the whole CSP. WI is consisted of NH4SCN, (NH4)2S2O3, FeSO4, PDS and hydroquinone accounting for 58.39%, 9.05%, 24.67%, 3.70%, and 3.37%, respectively, of the total WI. DI mainly contained polycyclic aromatic hydrocarbons, including benzenes, naphthalenes, fluorenes, phenanthrenes, anthraquinones and pyrenes. Carbon in OI existed mainly in the form of C–C and C–H, oxygen in OI existed in the form of C=O and C–OH groups. A composite extraction process was proposed to deal with CSP in this paper, which separated sulfur from impurities in CSP at normal temperature efficiently, based on the existing conditions of coking enterprises. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13023, 2019

Efficient preparation of cetyltrimethylammonium bromide-graphene oxide composite and its adsorption of Congo red from aqueous solutions

Materials based on graphene oxide (GO) have good adsorption capacities to various water contaminants in recent studies, owing to GO can provide more active sites than reduced graphene oxide. However, the inefficient preparation methods and tedious separation steps after adsorption limit their application in wastewater treatment. In this report, a facile method is proposed for the synthesis of a cetyltrimethylammonium bromide (CTAB)-GO composite via ionic interaction. The hydrophobicity of CTAB-GO composite is enhanced by the alkyl chains of CTAB, and thus, it can be readily separated from water-soluble impurities via low-speed centrifugation (3000 rpm for 3 min). The obtained CTAB-GO composite can efficiently remove the azo dye, Congo red from aqueous solutions, with an adsorption capacity as high as 2767 mg/g. Increasing the initial acidity of the solutions enhances the dye removal process. The adsorption kinetic studies reveal that the adsorption equilibrium achieves in ∼60 min, and the experimental data of the adsorption of Congo red fits well with the pseudo-second-order kinetic model and the Langmuir isotherm. Furthermore, the CTAB-GO composite presents good recyclability and the adsorption capacity is greater than 2000 mg/g even at the tenth cycle.

The influence of water-soluble impurities on thermal dehydration kinetics of phosphogypsum in self-generated atmosphere

The paper presents the results of studies of the effect of water-soluble impurities on the thermal dehydration of phosphogypsum in a self-generated atmosphere, which are obtained by thermogravimetry and differential scanning calorimetry. For comparison, the results of the thermal dehydration of gypsum are given. The information about the change in activation energy depending on the extent of the dehydration and the effect of temperature on the mechanism of the dehydration is obtained by the use of integral isoconversional and model-fitting methods. It has been established that water-soluble impurities have a significant influence on the kinetics of the dehydration. It has been shown that in the thermal dehydration of gypsum an abnormal change in the reaction rate and activation energy is observed. In the dehydration of phosphogypsum, this phenomenon is not observed. This is due to the impact of the water-soluble impurities on the recrystallization of an intermediate amorphous phase during the thermal decomposition.

Catalytic Hydrothermal Liquefaction of Food Waste Using CeZrOx

Approximately 15 million dry tons of food waste is produced annually in the United States (USA), and 92% of this waste is disposed of in landfills where it decomposes to produce greenhouse gases and water pollution. Hydrothermal liquefaction (HTL) is an attractive technology capable of converting a broad range of organic compounds, especially those with substantial water content, into energy products. The HTL process produces a bio-oil precursor that can be further upgraded to transportation fuels and an aqueous phase containing water-soluble organic impurities. Converting small oxygenated compounds that partition into the water phase into larger, hydrophobic compounds can reduce aqueous phase remediation costs and improve energy yields. HTL was investigated at 300 °C and a reaction time of 1 h for conversion of an institutional food waste to bio-oil, using either homogeneous Na2CO3 or heterogeneous CeZrOx to promote in situ conversion of water-soluble organic compounds into less oxygenated, oil-soluble products. Results with food waste indicate that CeZrOx improves both bio-oil higher heating value (HHV) and energy recovery when compared both to non-catalytic and Na2CO3-catalyzed HTL. The aqueous phase obtained using CeZrOx as an HTL catalyst contained approximately half the total organic carbon compared to that obtained using Na2CO3—suggesting reduced water treatment costs using the heterogeneous catalyst. Experiments with model compounds indicated that the primary mechanism of action was condensation of aldehydes, a reaction which simultaneously increases molecular weight and oxygen-to-carbon ratio—consistent with the improvements in bio-oil yield and HHV observed with institutional food waste. The catalyst was stable under hydrothermal conditions (≥16 h at 300 °C) and could be reused at least three times for conversion of model aldehydes to water insoluble products. Energy and economic analysis suggested favorable performance for the heterogeneous catalyst compared either to non-catalytic HTL or Na2CO3-catalyzed HTL, especially once catalyst lifetime differences were considered. The results of this study establish the potential of heterogeneous catalysts to improve HTL economics and energetics.

CONVERSION CALCIUM CARBONATE AS FILLER OF THERMOPLASTICS

X-ray and laser diffraction methods were used to determine basic physical and chemical properties of conversion calcium carbonate. It was found that for obtaining standard product for use as a filler, it is necessary to regrind it. The results of dispersion changes in conversion chalk (chalk stone) were expressed in terms of median (D50), maximum (D98) and minimum (D10) particle size. It was established that during the grinding process a transition occurs from the initial odiomodal distribution to the bimodal distribution, which is characterized by a sufficiently wide range of the sizes of the particles of the crushed material. The optimum parameters of grinding were determined. With the help of SEM method, used before and after grinding of conversion calcium carbonate, it was established that the particles of primary material are represented by polycrystalline dense aggregates of spherical shape, due to mass crystallization of calcium carbonate at the condition of high supersaturation according to polynuclear growth mechanism. The component composition of water-soluble impurities was quantitatively estimated on the basis of the determination of the content of nitrate N-NO3- and ammonium N-NH4+ forms of nitrogen in various forms of presence-total, bound, water-soluble, and additional determination of the Ca2+ content of calcium ions in aqueous extract. It has been experimentally established that preliminary heat treatment of conversion calcium carbonate allows to significantly reduce the total content of water-soluble substances in the ground product by more than 5 times: at a temperature of 400 ° C, the degree of removal by NH4+ and NO3- ions is ~ 40-50%, and at 500 ° C - ~ 60% for NO3- and ~ 90% for NH4+. The estimation of the possibility of using the obtained product as a filler of polymer composite materials was done comparing the main parameters (CIELab (W and L) color characteristics, bulk density, dispersed composition, specific surface, pH of aqueous extract) with known finely ground natural chalk and microcalcite. Forcitation:Rudakova L.V., Niftaliev S.I., Natarova E.S. Conversion calcium carbonate as filler of thermoplastics. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 4. P. 100-107.

High-Purity Amino-Functionalized Graphene Quantum Dots Derived from Graphene Hydrogel

The unique properties of graphene quantum dots (GQDs) make them interesting candidate materials for innovative applications. Herein, we report a facile method to synthesize amino-functionalized graphene quantum dots (AF-GQDs) by a hydrothermal reaction. Graphene oxide (GO) was synthesized by Hummer’s method where ultra-small GO sheets were obtained by a prolonged oxidation process followed by sonication using an ultrasonic probe. Subsequently, graphene hydrogel (GH) was also obtained by a hydrothermal synthesis method. Proper care was taken during synthesis to avoid contamination from water soluble impurities, which are present in the precursor, GO solution. Following the treatment of GH in ammonia, ultra-small amino-functionalized graphene fragments (AF-GQDs) were formed, which detached from the GH to eventually disperse evenly in the water without agglomerating. This modified synthesis process enables the formation of high-purity AF-GQDs (99.14%) while avoiding time-consuming synthesis procedures. Our finding shows that AF-GQDs with sizes less than 5[Formula: see text]nm were well dispersed. A strong photoluminescence (PL) emission at [Formula: see text]410[Formula: see text]nm with 10% PL quantum yield was also observed. These AF-GQDs can be used in many bio applications in view of their low cytotoxicity and strong fluorescence that can be applied to cell imaging.

The Effect of Roasting Temperature at 400C and Sulphuric Acid Concentration on TiO2 Extraction Process from Zircon Sand Ilmenite

In this research, roasting temperature at 400C and sulphuric acid concentration variations was conducted to obtain titanium dioxide from zircon sand. The research was done through extraction metallurgy method which involved physical, chemical, and mechanical treatments. Zircon was magnetically separated, mixed with NaOH, and roasted with temperature of 400C. Characterization with XRD of the sample before and after magnetic separation was conducted. Peaks obtained from NaFeO2, NaTiO2, Na0.75Fe0.75Ti0.25O2, and TiO2 compounds were observed. In this study, the leaching process lasted in two stages. For the first leaching samples of combustion products are leached using distilled water to remove water-soluble impurities. For the second stage, the deposition obtained from stage one is leached using 8, 10, and 12 M concentrated sulphuric acid at high temperature to dissolve iron. XRD was used to characterize TiO2. The result showed that the sample at temperature of 400C and concentrated sulphuric acid of 12Mis whiter in colour compared to other samples. Furthermore, at temperature 400C and concentrated sulphuric acid of 12 M, the titanium dioxide produced is 32.3% and 11.5% for rutile and anatase, respectively.

Comportamento de superfosfato simples contendo fosfato de ferro de baixa solubilidade em água em solos de várzea do Rio Grande do Sul

Algumas rochas utilizadas na produção de fertilizantes contêm impurezas de baixa solubilidade em água, destacando-se alguns fosfatos de Fe e Al, que poderiam ser aplicados em solos alagados, onde as reações de redução podem aumentar a solubilidade. O objetivo deste trabalho foi estudar a liberação do P de fertilizantes contendo impurezas de fosfatos de Fe com baixa solubilidade em água em diferentes solos de várzea do Rio Grande do Sul (RS) sob condições de alagamento. Para realização do experimento foram utilizados seis solos de várzea (dois Gleisssolos, dois Planossolos e dois Chernossolos) de diferentes locais do Estado do Rio Grande do Sul, os quais foram acondicionados em vasos plásticos de 8 L. Cada solo recebeu duas fontes de P (superfosfato simples e superfosfato simples com resíduos de Fe) e uma testemunha sem adição de P, com três repetições. Nos tratamentos com P foram adicionados ao solo 100 mg kg-1 P no solo. Os solos foram alagados e mantidos, em delineamento inteiramente casualizado e três repetições, com uma lâmina de água de 5 cm de altura acima de sua superfície. A solução do solo foi coletada semanalmente, sendo medidos imediatamente o pH e o potencial redox (Eh); posteriormente, procedeu-se, em laboratório, à determinação dos teores de P e Fe. Os resultados mostram redução do Eh e aumento do pH e dos teores de Fe e P em solução para todos os solos. O teor de P na solução não diferiu quanto à fonte, mostrando que o superfosfato simples com impurezas de fosfato de Fe tem potencial de uso em solos de várzea do Rio Grande do Sul cultivados com arroz irrigado por alagamento, mesmo sem a solubilidade em água prevista na legislação brasileira.

Purification of Nano‐Porous Silicon for Biomedical Applications

AbstractRecently, various bio‐medical applications of nanoporous silicon (np‐Si) have been suggested. This work investigates the biocompatibility of np‐Si particles taking into account hazardous residua confined in the pores after preparation. The emphasis is on the potential application of such particles as oxygen photosensitizer for photodynamic therapy of cancer, which requires both negligible toxicity of np‐Si particles in darkness and a high photo‐cyto‐toxic effect due to generation of singlet oxygen under illumination. Considerable amounts of water soluble toxic impurities are found to be present in the nanoporous shell of micrometer‐sized np‐Si particles immediately after their preparation by chemical etching of bulk silicon powder. The effects of several ordinary cleaning treatments are investigated by using thermal effusion mass‐spectroscopy and FTIR spectroscopy. A particular purification procedure is developed, capable to reduce the concentration of residual impurities to levels acceptable for bio‐medical applications while preserving the required photo‐activity of the np‐Si particles.

Preparation of GSH-functionalized porous dextran for the selective binding of GST by high internal phase emulsion (HIPE) polymerization

Well-defined porous dextrans bound with glutathione (GSH) were prepared in four steps: (1) vinylation of dextran by reacting it with glycidyl methacrylate (GMA), (2) preparation of the aqueous phase with vinylated dextran, surfactant and reduced GSH, (3) HIPE polymerization of vinylated dextran initiated by AIBN in an oil phase and incorporating GSH onto the dextran chains by chain transfer reactions, and (4) removal of the oil phase and water soluble impurities. These porous materials had interconnected pores, very thin walls and enough GSH moieties for glutathione S-transferase (GST) separation via specific GSH-GST binding. The representative material prepared was filled in the column for separation of the GST from the crude cell lysate. The result shows that this material has a very high selectivity for GST separation.

Effects of Ozone Dissolved in Water on the Physicochemical Properties of Activated Carbons Applied in Drinking Water Treatment

The results of treating commercial granulated activated carbons with ozone, both gaseous and dissolved in water, were analyzed. The original carbons (Filtrasorb-300 and Carbsorb-38) were carefully flushed with distilled water to remove any water-soluble impurities. For comparison, each of the washed activated carbons was treated separately with aqueous hydrogen peroxide. The following procedures were applied to assess the effects of contact between each carbon and the oxidizing agents: thermogravimetry, alkalimetry, voltammetry, EDX and FT-IR methods to illustrate changes in the surface chemistry, and nitrogen low-temperature adsorption to show up any possible changes in the porous structure. Ozone dissolved in water exhibited the lowest oxidative strength — EDX and FT-IR spectroscopy revealed only a slight oxidation of the Filtrasorb-300 surface layer. Despite its smaller specific area, this carbon surface exhibited greater roughness and was more susceptible to oxidation. The liquid-phase adsorption isot...

Salt inclusions in polar ice core: Location and chemical form of water-soluble impurities

Ice cores retrieved from ice sheets provide the most detailed records of climate over the past several hundred thousand years. For example, water-soluble impurities have been used as proxies for atmospheric chemistry. However, numerical models warned that the distributions of the trace constituents are significantly altered by rapid diffusion through liquid veins along triple junctions during ice sheet flow. Although these calculations assumed that the trace constituents are preferentially confined to grain boundaries and form a vein network, this assumption has not been confirmed experimentally. Using micro-Raman spectroscopy, here we show that most of the soluble impurities are confined as salt inclusions within grains. These inclusions are mainly composed of the sulfate salts Na 2SO 4·10H 2O, MgSO 4·12H 2O, and CaSO 4·2H 2O. We also found that methane-sulfonate salts and other complex salts exist only in the glacial-period ice. Our findings imply that these salts form within 185 m of the ice surface and then preserve their composition as the ice is pushed to greater depths. This means that depth profiles of the trace constituents should be preserved in deep ice cores as reliable proxies for past climate.

Isolation and purification of lutein from the microalga Chlorella vulgaris by extraction after saponification.

A simple and efficient method for the isolation and purification of lutein from the microalga Chlorella vulgaris was developed. Crude lutein was obtained by extraction with dichloromethane from the microalga after saponification. Partition values of lutein in the two-phase system of ethanol-water-dichloromethane at different ratios were measured by HPLC so as to assist the determination of an appropriate condition for washing water-soluble impurities in the crude lutein. Partition values of lutein in another two-phase system of ethanol-water-hexane at different ratios were also measured by HPLC for determining the condition for removing fat-soluble impurities. The water-soluble impurities in the crude lutein were removed by washing with 30% aqueous ethanol, and the fat-soluble impurities were removed by extraction with hexane. The final purity of lutein obtained was 90-98%, and the yield was 85-91%.

MULTIPLE-EFFECT EVAPORATION REGIME IN HIGH-PRESSURE BOILERS

In the 1930’s, a multiple-effect evaporation technique was proposed for generating clean steam that was based on the use of boiler drums partitioned into sections for processing boiler water with different salt concentration [1]. In a sectioned drum, the “clean” section served for generating steam with a salt concentration lower than that in the steam generated in the “salt collection” section; the steam flowing from the two sections was mixed together to produce a steam with rated characteristics required for normal operation of superheaters and turbines. The method in question is quite satisfactory for low-pressure boilers in which requirements placed on the quality of steam are too stringent and can be provided by use of simple water treatment techniques. Numerous data have been reported in the literature that were mainly focused on the advantages of drum boilers with multiple-effect evaporation for generating standard-quality steam. It was shown in [2] that in steam generators using steam washing techniques that gained wide acceptance in the 1950’s, the continued application of multiple-effect evaporation added little (if any) to the quality of steam. Therefore in view of the ever-increasing requirements placed on the quality of feed water supplied at higher pressures (which caused the increase in impurities, especially silicic acid, in steam), the advisability of using multiple-effect evaporation in high-pressure boilers was questioned in a number of works [3–7]. At present, even in the use of incompletely desalinized water for feeding high-pressure (HP) boilers at thermal power plants (TPPs), no problem arises with the quality of steam produced either by multiple- or single-effect evaporation (domestic TP-100-, VPG-250-, and TPE-214-type boilers, as well as boilers available from foreign manufacturers, or medium-pressure boilers currently in service in Russia). As is known, the performance of an evaporating heating surface is to a significant extent determined by the rate at which inside fouling deposits build up. With this in mind, it is important to consider the water-and-salt regime (WSR) for the boiler water fed to drum boilers with multiple-effect evaporation. The annual rate of faults in the water-wall tubes of drum boilers (bulging, corrosion) is rather high, whereas these faults seldom (if ever) occur in high-pressure and supercritical-pressure (SCP) direct-flow boilers. The reason for this is that, with the feed water of the same quality, the boiler water for the cooling water wall of drum boilers contains soluble impurities in concentrations higher than that for direct-flow boilers (by a factor of 100 against the feed water at a 1% blow-down), which creates favorable conditions for the buildup of deposits and corrosion. Water-soluble impurities (Ca, Mg, Na, SiO2 salts, etc.) are removed from the drum boiler via continuous blow-down. Therefore requirements placed on the quality of boiler water and, consequently, feed water for drum boilers in terms of soluble impurities can be less stringent than for direct-flow boilers: in the latter, all the impurities are confined within the water-steam circuit. As to iron oxides, the situation is somewhat different; most iron oxides deposit inside the water-wall tubes and are not removed readily by blow-down. With the increase in operating pressure, requirements placed on the quality of boiler water and, consequently, feed water become more stringent — with a view to preventing corrosion and fouling of the wa

Extraction of Water-Soluble Impurities from Fly Ash

This study focuses on the behavior of major and trace water-soluble impurities in fly ash during leaching processes. The objective is to assess potential decontamination procedures in order to reduce the content of undesirable species in coal combustion by-products and to increase their potential industrial applications. Fourteen flyashes were selected for this study. Major impurities considered were lime and portlandite, sulfate, and some potentially hazardous trace elements such as As, Ba, Be, Cd, Co, Cr, Cu, Ge, Mn, Mo, Ni, Pb, Se,Th, U, V,and Zn.Water was used for the extraction experiments,with asolvent/fly ash ratio of 50 mL/g. An hydrite was completely dissolved in all fly ashes studied, except the Cercs and Escatron flyashes. Lime and portlandite were completely dissolved or carbonated from all flyashes with exception of the Cercs flyash. Bulk calcium contents were reduced from 9% to 18% in all fly ashes with the exception of the Compostilla and Espiel fly ashes (4-5%). From 17% to 79% ofthe sulfur was extracted from the bulk content. The results show a relatively higher extraction for S, Se, As, B, Mo, and Ca, and an intermediate extraction for As, Ge, Cd, Li, Sr, Na, V, Cr, Sn, P, and Ba. The results suggest that the alkalinityis induced during the extraction mainly by free lime. The high alkalinity accounts for the high Al and Si concentrations in the leachates and the relatively low mobility of sometrace elements, with the exception of As, B, Mo, and Se.

Automated high-throughput liquid-liquid extraction for initial purification of combinatorial libraries.

An automated high-throughput liquid-liquid extraction (LLE) methodology has been developed and utilized for the initial purification of the combinatorial library samples containing unreacted amines and other water-soluble byproducts or impurities. Various extraction solvents were evaluated along with different extraction devices. The LLE method was automated using 96-well-format plates and a robotic liquid-handling workstation. In the optimized LLE method, crude combinatorial library samples were dissolved in a water-immiscible organic solvent, butyl acetate, and added to each well in a 96-well-format plate packed with an inert support material coated with hydrochloric acid. Separation occurs based on the partitioning of the compounds between two liquid phases. Product recovery, purity, and amine removal efficiency were determined by HPLC with and without precolumn derivatization. The automated method was successfully applied to the cleanup of some representative combinatorial library samples with greater than 98% amine removal and an average product purity of 90%. The application of the automated high-throughput LLE method should greatly reduce the labor, time, and cost associated with the purification of combinatorial libraries.

Water uptake of soft lining materials from osmotic solutions

Objectives: The water uptake characteristics of soft lining materials are of obvious importance in that they are expected to function in the oral environment. Results for Novus (Hygenic Corp., Akron, OH, USA) show a very high uptake from distilled water. Despite this high uptake, Novus appears to function satisfactorily in the mouth. High water uptake of soft lining materials has been attributed to the presence of water soluble impurities that, on immersion, form solution droplets; the driving force for the uptake being the osmotic gradient between the droplets and the external solution. Uptake should therefore be less from ionic solutions. The object of this study was to test the applicability of this theory to Novus and two experimental soft lining materials. Methods: Water uptake of two experimental materials and Novus has been determined from distilled water and two saline solutions (0.45 and 0.9 M). After 196 days specimens were desorbed to constant weight and then subjected to a second sorption cycle. Results: Novus had the highest uptake from distilled water at ~18%, the experimental materials having an uptake ~7%. Desorptions were all rapid, minimum weight being reached within 1–2 days. Uptakes of the second sorptions from water were all higher. Uptake from saline solutions was ~1–2% for all materials, uptake from 0.9 M saline being the lowest. Second sorption results from solution were similar to the first. Conclusion: The results obtained support the theory that the high water uptake of elastomeric materials is osmotically driven.

Surface potential studies of monolayers of surfactant donor and acceptor molecules

The surface potential technique was used for investigation of donor, acceptor and mixed monolayers, containing molecules suitable for deposition of conducting LB films. It is shown that the donor and acceptor monolayers are neutral at the air-water interface. Big positive values of surface potential in the case of donor molecules are explained by peculiarities of dipole depolarization near the surface of the water and by charge transfer salt formation with water-soluble impurities. The dipole moment arising due to charge transfer between donor and acceptor molecules in mixed monolayers is parallel to the layer plane. Other details of charge transfer complexes or salt formation in the mixed monolayers are discussed.

Effects of long‐chain alkyl peroxydicarbonates on the properties of PVC produced by suspension polymerization

AbstractCommercially available diethyl, dicetyl, and dimyristyl peroxydicarbonate initiators are investigated in a commercial PVC suspension polymerization receipe. Diethyl peroxydicarbonate, which is formed in situ by the reaction of hydrogen peroxide, lime, and ethylchloroformate, produced PVC with less “fish‐eyes”, whereas it has the disadvantage of being toxic and gives inconsistent polymerization times, therefore the reactor efficiency decreases. Dicetyl and dimyristyl peroxydicarbonates are solid, less toxic materials easy to handle, therefore, when these initiators are used, consistency between batches is obtained. However, PVC with coarse particle sizes containing considerable amounts of “fish‐eyes” is obtained, which eventually causes processing problems. It is found that particle coarsening occurs as a result of water soluble impurities of initiators, and “fish‐eyes” occur as a result of morphological changes. When dicetyl and dimyristyl type initiators are used, the number of non‐porous PVC particles increases. This structure heterogeneity causes formation of ungellified spots, so‐called “fish‐eyes”, during processing. It is found that the non‐porous particles are formed due to accumulation of an excessive amount of initiator in a single vinyl chloride monomer droplet.When the distribution of these solid initiators is homogenized by adding them in solution, the formation of non‐porous particles is inhibited. However, the coarsening effect still remains, which could be eliminated by extraction of initiator solutions with water just before they are fed to the reactor. Extraction also decreases the amount of crust formation.

Mutagenic contaminants in synthetic peptides obtained by an azide coupling

Hormone-like peptides are, almost by definition, not mutagenic. It was, therefore, unusual to find that some batches of peptides synthesized by azide coupling were mutagenic in the Ames test. One of these peptides, eledoisin, showed mutagenic activity particularly in Salmonella typhimurium TA 1535 without metabolic activation. This activity was independent of the peptide purity determined by HPLC and a dose response relationship was observed at concentrations over the solubility limit of the peptide in the assay medium. We therefore suggested that the mutagenic effect might be due to the presence of chemically undetectable, water-soluble impurities, which could be removed by counter-current distribution. If, however, the same final coupling was carried out by the mixed anhydride procedure, no mutagenic activity was observed. Consequently, we considered that the mutagenicity detected was due to traces of hydrazoic acid salts arising during azide formation in the coupling step. In fact only the product of the coupling reaction between the pivotal intermediates was mutagenic.