Dilute Sodium Hydroxide Solution Research Articles

Influence of baking conditions and precursor supplementation on the amounts of the antioxidant pronyl-L-lysine in bakery products.

The influence of baking conditions and dough supplements on the amounts of the antioxidant and Phase II-Enzyme modulating, protein-bound 2,4-dihydroxy-2,5-dimethyl-1-(5-acetamino-5-methoxycarbonyl-pentyl)-3-oxo-2H-pyrrol (pronyl-L-lysine) in bakery products was investigated in quantitative studies. These studies revealed high amounts of the antioxidant in bread crust, only low amounts in the crumb, and the absence of this compound in untreated flour. The amounts of pronyl-L-lysine were found to be strongly influenced by the intensity of the thermal treatment. For example, increasing the baking time from 70 to 210 min or increasing the baking temperature from 220 to 260 degrees C led to a 5- or 3-fold increase in the concentrations of this antioxidant in the crust, respectively. In addition, modifications in the recipe showed to have a major impact on pronyl-L-lysine formation. For example, substituting 5% of the flour with the lysine-rich protein casein or with 10% of glucose increased the amounts of the antioxidant by more than 200%. Quantitative analyses of commercial bread samples collected from German bakeries revealed the highest amount of 43 mg/kg for a full grain bread, followed by a rye/wheat bread, both of which have been sourdough fermented. A mixed-grain bread as well as pale wheat bread, both prepared without sourdough fermentation, contained significantly lower amounts of pronyl-L-lysine, and German pretzels, which are treated with a dilute sodium hydroxide solution prior to baking, contained only trace amounts of pronyl-L-lysine (e.g., less than 5 mg/kg were detectable in pretzels). Systematic studies revealed that the decrease of the pH value induced by microbial acid formation during sourdough fermentation is the clue for producing high amounts of pronyl-L-lysine in baking products. These data clearly demonstrate for the first time that the amounts of the antioxidant and chemopreventive compound pronyl-L-lysine in bakery products is strongly dependent on the manufacturing conditions as well as the recipe.

The alkaline stability of phosphate coatings II: in situ Raman spectroscopy

In situ Raman spectroscopy was used to study the dissolution of phosphate layers on zinc coated steel in dilute sodium hydroxide solution. The Raman intensity of the symmetrical stretching vibration of the phosphate anion was used to quantify the relative amount of phosphate on the surface. During exposure to an alkaline electrolyte, the intensity was found to decrease in a near linear manner, indicative of the removal of the phosphate anion. Crystal layers containing secondary ions Mn 2+ and Ni 2+ showed an improved stability compared to monocation zinc phosphate layers. The formation of amorphous Mn-hydroxide was observed on phosphate layers containing manganese.

Preparation of cellulose samples for size-exclusion chromatography analyses in studies of paper degradation

Hydrolytic degradation of cellulose was shown to take place during the activation procedure in distilled water during the dissolution procedure of cellulose samples from papers for size-exclusion chromatography analyses in the lithium chloride– N, N-dimethylacetamide (DMAc) solution system. The use of dilute aqueous sodium hydroxide solution in the activation procedure prevents hydrolytic degradation of cellulose during the dissolution procedure, especially in the case of samples of aged papers with low pH. The use of the freeze-drying technique provides samples of cellulose ready-made for dissolution in lithium chloride– N, N-dimethylacetamide solution.

Anodic behaviour of arsenopyrite and cathodic reduction of ferrate(VI) and oxygen in alkaline solutions

This paper presents the results of an electrochemical study of the anodic characteristics of arsenopyrite in strongly alkaline solutions and of the cathodic reduction of ferrate(VI) and of dissolved oxygen at an arsenopyrite surface at potentials which are relevant to the oxidation reactions. Cyclic voltammetry at both arsenopyrite disc and arsenopyrite disc/platinum ring electrodes has shown that arsenic(III) is the main product of the anodic process at potentials in the region of the rest potential during oxidation by either ferrate(VI) or oxygen. Evidence for partial passivation of both the anodic and cathodic reactions has been obtained from potentiostatic current–time transients. The initial stage of oxidation by ferrate(VI) has been shown to be mass-transport controlled and this is also true of the oxidation by oxygen in dilute solutions of sodium hydroxide.

Determination of Isoflavones in Soy and Selected Foods Containing Soy by Extraction, Saponification, and Liquid Chromatography: Collaborative Study

Isoflavones are biologically active compounds occurring naturally in a variety of plants, with relatively high levels found in soybeans. Twelve laboratories participated in a collaborative study to determine the aglycon isoflavone content of 8 test samples of soy and foods containing soy. The analytical method for the determination of isoflavones incorporates a mild saponification step that reduces the number of analytes measured and permits quantitation versus commercially available, stable reference standards. Test samples were extracted at 65 degrees C with methanol-water (80 + 20), saponified with dilute sodium hydroxide solution, and analyzed by reversed-phase liquid chromatography with UV detection at 260 nm. Isoflavone results were reported as microg/aglycon/g or microg aglycon equivalents/g. The 8 test samples included 2 blind duplicates and 4 single test samples with total isoflavone concentrations ranging from approximately 50 to 3000 microg/g. Test samples of soy ingredients and products made with soy were distributed to collaborators with appropriate reference standards. Collaborators were asked to analyze test samples in duplicate on 2 separate days. The data were analyzed for individual isoflavone components, subtotals of daidzin-daidzein, glycitin-glycitein, and genistin-genistein, and total isoflavones. The relative standard deviation (RSD) for repeatability was 1.8-7.1%, and the RSD for reproducibility was 3.2-16.1% for total isoflavone values of 47-3099 microg/g.

Photochemical reduction of hexavalent chromium in glycerol-containing solutions

Hexavalent chromium [Cr(VI)] in the form of potassium dichromate was photochemically reduced to trivalent chromium [Cr(III)] in aqueous solutions containing glycerol. This reaction occurred rapidly during irradiation with either unfiltered sunlight or a UVA-emitting light source. Photochemical reduction of Cr(VI) was pH-dependent and did not occur in dilute solutions of sodium hydroxide. In acidified solutions, the reduction occurred at elevated rates and at lower concentrations of glycerol. This reaction was found to be dependent on the unsubstituted alcohol groups of glycerol since alpha-phosphoglycerol and beta-phosphoglycerol did not support the photochemical reduction of Cr(VI). These findings suggest that glycerol or related polyols can be used for the remediation of hexavalent (toxic) chromium at contaminated environmental sites.

Chemical Method for Determination of Carbon Dioxide Content in Egg Yolk and Egg Albumen

The safety, quality, and shelf life of shell eggs is a function of carbon dioxide content. A commercial process was recently developed for rapidly cooling shell eggs by using cryogenic CO2. The benefit of this new process over existing cooling processes is that the CO2 addition during cryogenic cooling provides additional safety and quality enhancements. In order for these benefits to be fully developed into a process that can be adopted by the egg industry, and thus realized by the consumer, the amount of CO2 absorbed by the egg during this process needs to be quantified. Because the albumen pH of rapidly cooled eggs was reduced to pH <6.5, existing titrametric methods were not adequate for determining CO2 content. They did not prevent CO2 loss during neutralization. A simple and accurate method for determining CO2 content in acidified egg albumen and yolk samples was developed. This method involves the liberation of CO2 from an acidified egg sample into a standardized, dilute sodium hydroxide solution inside a sealed jar. The egg sample and a small beaker containing the standardized sodium hydroxide solution are placed in a glass jar and sealed. Next, a concentrated acid phosphate solution is injected through a rubber septum in the cap of the jar onto the egg sample, while avoiding contact with the sodium hydroxide solution. The sample is then stored at 37 C for 24 h. During this storage period, the carbon dioxide is released from the egg sample and is absorbed into the sodium hydroxide solution. Afterwards, the dilute sodium hydroxide solution is removed and titrated to the phenolphthalein endpoint using a dilute, standardized hydrochloric acid solution. The amount of hydrochloric acid solution required for neutralization can be directly related to CO2 content in the sample.

Specific spectrophotometric determination of hydrocyanic acid in the environment

A very simple, sensitive and specific method for the determination of hydrocyanic acid in air and water is described. Hydrocyanic acid is collected in dilute sodium hydroxide solution and then reacted at pH 7 and 100 °C with picric acid solution, forming 2,6-dinitro-5-hydroxy-4-hydroxylamino-1,3-dicyanobenzene. The absorbance of the red solution is read at 505 nm. The color system obeys Beer’s law in the range 0.1–10 mg m−3 hydrocyanic acid (0.2–20 μg g−1). The collection efficiency of the absorbing solution and the molar absorptivity (1.42 × 103 l mol−1 cm−1) were evaluated. All other important analytical parameters were studied and the method was applied to the determination of hydrocyanic acid in air samples and cigarette smoke.

Case study: Choosing selective catalytic reduction as a preferred technology for the destruction of NOx

AbstractChoosing an environmental control technology for destroying oxides of nitrogen (NOx) became essential when Engelhard, a manufacturer of automotive catalysts, included inorganic nitrate compounds in their formulations. Heat treating catalysts inside a high temperature oven causes these compounds to decompose, producing NOx and other gaseous by ‐ products, including volatile organic compounds (VOCs). Local environmental regulations limit the maximum concentration of total NOx to 200 parts per million (ppmv). The NOx continuously emitted from the oven can reach concentrations of up to 10,000 ppmv with VOC levels reaching 500 ppmv. Therefore, an emissions control strategy needed to be implemented.The exhaust temperature of this mixed gas stream operates at an average temperature of 230°C. The composition of the different oxidation states of NOx stays relatively constant at 30% nitrogen dioxide (NO2) and 70% nitric oxide (NO). Utilizing a scrubber column packed with high surface are a packing to affect intimate contact between the gas and absorbing liquid in a countercurrent flow pattern, resulted in a 60% maximum NOx destruction efficiency. The absorbing liquid was a dilute solution of sodium hydroxide. Since nitric oxide is insoluble, it must be oxidized to NO2 before diffusing across the mass transfer interface into the liquid phase in order to react with caustic soda and form sodium nitrate. A more sophisticated wet scrubbing process uses several columns arranged in series. First, it quenches the inlet gas stream, then oxidizes nitric oxide to nitrogen dioxide, after which the NO2 is absorbed into the scrubbing solution. Process control of scrubbing fluid concentrations and gas flows is vital to maintaining constant high levels of NOx destruction efficiency. The secondary wastewater stream may have to be treated prior to discharging it into the city's sewer system. In order to destroy VOCs, a separate pollution abatement process, in series with the NOx scrubbing columns, would have to be installed. The combined environmental control system is quite complex and requires a high capital investment.The alternative NOx and VOC control technology uses a single skid mounted system, combining selective catalytic reduction (SCR) for the destruction of NOx and an oxidation catalyst for VOC removal. Most SCR catalyst systems used in the industry today abate NOx from stationary power generating sources with lower NOx concentrations that operate 24 hours per day and 365 days per year. However, SCR technology is slowly becoming a more popular option to reduce NOx from chemical manufacturing facilities because of its efficiency to destroy NOx and process flexibility to handle varying concentrations of NOx.In 1988, Engelhard's automotive catalyst manufacturing plant located in Huntsville, Alabama designed and installed its first SCR catalyst system to reduce NOx to nitrogen and water from a high temperature furnace exhaust gas. Since then, several combination SCR/VOC catalyst systems have been installed at Engelhard's automotive catalyst manufacturing facilities around the world. These systems have proven successful. They are highly efficient, the equipment is easy to maintain and operate, they do not produce a secondary waste stream (low ammonia slip) and have relatively low capital cost compared to other available technologies.

Sampling and determination of hydrogen cyanide in cigarette smoke

A method for sampling and determination of hydrogen cyanide in cigarette smoke is described. Cigarette smoke is filtered through a glass fiber filter paper, and only gaseous compounds, such as hydrogen cyanide, are collected in a dilute sodium hydroxide solution. The cyanide is determined spectrophotometrically at 550 nm by the isonicotinic acid–pyrazolone method. Maximum absorbance is achieved within 10 min at room temperature, and remains constant for about 20 min. Beer’s law is obeyed in the range 0.04∼0.80 μg mL–1 cyanide, with a molar absorptivity of 3.48 × 104 L mol–1 cm–1.

Diazoacetaldehyde: completion of the rate profile for hydration of its photo-Wolff rearrangement product, ketene, in aqueous solution and kinetics and mechanism of acid-catalyzed hydrolysis of the diazoaldehyde †

Ketene was generated flash photolytically by the photo-Wolff reaction of diazoacetaldehyde and rates of its hydration to acetic acid were measured in dilute aqueous sodium hydroxide solution. The results give the isotope effect, kHO/kDO = 0.87, on the hydroxide-ion catalytic coefficient for this reaction, and, together with literature information, they provide a complete rate law for the hydration of ketene in aqueous solution promoted by solvent related species: kobs/s–1 = 1.01 × 104[H+] + 3.65 × 101 + 5.26 × 104[HO–]. Rates of hydrolysis of diazoacetaldehyde in dilute perchloric acid solution were also measured and an inverse hydronium ion isotope effect was found: kH+/kD+ = 0.55. That, plus the fact that hydrogen exchange of the diazo hydrogen atom of diazoacetaldehyde takes place more rapidly than its hydrolysis, shows that hydrolysis occurs through a mechanism involving pre-equilibrium protonation of diazo carbon followed by rate-determining loss of nitrogen.

Membrane Cleaning: Chemically Enhanced Removal of Deposits Formed During Yeast Cell Harvesting

Cleaning strategies have been evaluated for a microfiltration membrane fouled during cell harvesting. The membrane selected was a flat sheet of hydrophilic polyethersulphone with a nominal pore size of 0.1 μm. Baker’ s yeast was selected as a model micro-organism. During microfiltration, a constant transmembrane pressure of 2 bar, cross-flow velocity of 1ms−1, and suspension temperature of 34°C produced a steady state flux within 90 minutes. A water rinse removed the majority of the cellular cake revealing tenacious non-cellular and cellular deposits. Chemically enhanced cleaning of the rinsed deposit was investigated using dilute solutions of sodium hydroxide, nitric acid and P3 Ultrasil 11. Cleaning temperature effects were investigated over the range 30°C to 60°C and laminar and turbulent flow regimes were compared. A combination of measured flux recovery and microscopic visualization was used to assess cleaning performance. Effective two-stage cleaning was achieved with sequential alkali and acid treatments while effective single-stage cleaning was achieved using the formulated detergent P3 Ultrasil 11.

Trace Determination of Strong Acids in NitroPlasticizers

A titration method was applied to the trace determination of strong acids in a variety of nitro plasticizers. The analyses were performed in acetonitrile using an automatic titrator and a calomel combined glass electrode for non-aqueous solutions. A dilute solution of sodium hydroxide (5.00 × 10 - 4 M) in methanol was used as the titrant. The sensitivity and precision of the method were greatly increased by the addition of a known volume of dilute nitric acid to the solvent in which the titrations were performed. Very low acid content values were detected in the plasticizers with the experimental conditions used. The detection limit was found to be 0.001 mg g - 1 of NaOH in the sample (0.000025 m equiv. g - 1 ) and the measured acid content values were reproducible.

Extraction of phosphorus, arsenic and/or silica from sodium tungstate and molybdate solutions with primary amine and tributyl phosphate as solvents. I — Synergistic extraction and separation of phosphorus, arsenic and/or silica from tungstate and molybdate solutions

Studies on the synergistic extraction of phosphorus, arsenic and silica as impurities from sodium tungstate and molybdate solutions with a solvent mixture of primary amine and tributyl phosphate (TBP) were made. The experimental results indicate that phosphorus, arsenic and silica can be extracted and separated very effectively from weakly alkaline sodium tungstate and neutral molybdate solutions. The extraction behavior of phosphorus and arsenic for molybdate systems is quite different from that for tungstate systems. For molybdenum systems, the optimum separation of phosphorus and arsenic can only be obtained in a narrow range of equilibrium pH values of about 6–7; outside this pH range the extraction of these two elements decreases sharply. However, the extraction of phosphorus, arsenic and silica for tungsten systems and silica for molybdenum system increases with decreasing pH. Phosphorus, arsenic and silica cannot be extracted without the presence of tungsten and molybdenum in the aqueous phase. The loaded organic phase can be stripped with dilute sodium hydroxide solution quantitatively. The alkaline crude leaching solutions of sodium tungstate and ammonium molybdate were tested and the results were in agreement with those obtained from solutions prepared by mixing sodium salts of the elements concerned.

Ion association of dilute aqueous sodium hydroxide solutions to 600�C and 300 MPa by conductance measurements

The limiting molar conductances Λ0 and ion association constants of dilute aqueous NaOH solutions (<0.01 mol-kg−1) were determined by electrical conductance measurements at temperatures from 100 to 600°C and pressures up to 300 MPa. The limiting molar conductances of NaOH(aq) were found to increase with increasing temperature up to 300°C and with decreasing water density ρw. At temperatures ≥400°C, and densities between 0.6 to 0.8 g-cm−3, Λ0 is nearly temperature-independent but increases linearly with decreasing density, and then decreases at densities <0.6 g-cm−3. This phenomenon is largely due to the breakdown of the hydrogen-bonded, structure of water. The molal association constants K Am for NaOH( aq ) increase with increasing temperature and decreasing density. The logarithm of the molal association constant can be represented as a function of temperature (Kelvin) and the logarithm of the density of water by $$\begin{gathered} log K_{Am} = 2.477 - 951.53/T - (9.307 \hfill \\ - 3482.8/T)log \rho _{w } (25 - 600^\circ C) \hfill \\ \end{gathered} $$ which includes selected data taken from the literature, or by $$\begin{gathered} log K_{Am} = 1.648 - 370.31/T - (13.215 \hfill \\ - 6300.5/T)log \rho _{w } (400 - 600^\circ C) \hfill \\ \end{gathered} $$ which is based solely on results from the present study over this temperature range (and to 300 MPa) where the measurements are most precise.

The hydration of mesitylketene in aqueous solution: detection of acid catalysis for an aromatic ketene

Mesitylketene was generated flash photolytically in aqueous solution by the photo-Wolff reaction of 2,4,6-trimethyldiazoacetophenone and also by rearrangement of mesitylynol obtained through photodecarbonylation of mesitylhydroxycyclopropenone, and rates of hydration of this ketene were measured in dilute perchloric acid, sodium perchlorate, and sodium hydroxide solutions as well as in concentrated sodium perchlorate and perchloric acid solutions. In dilute solution only an uncatalyzed reaction and a sodium-hydroxide-catalyzed process were observed, both of which could be attributed to nucleophilic attack, by water and by hydroxide ion, respectively, at the ketene carbonyl carbon atom. In concentrated sodium perchlorate solutions, a mild decrease in reaction rate with increasing salt concentration was observed, as expected on the basis of decreasing water activity and a consequent slowing of the uncatalyzed reaction. A similar mild decrease was found in perchloric acid solutions up to [Formula: see text] but this then gave way to a rate increase that became dominant above [Formula: see text] This appearance of acid catalysis indicates a change in reaction mechanism from nucleophilic attack of water to an electrophilic process involving rate-determining protonation on the β-carbon atom of the ketene group. Analysis of the acid-catalyzed reaction rate by the Cox–Yates method gives the catalytic coefficient [Formula: see text] This, when compared with [Formula: see text] for ketene itself, shows that the mesityl group retards acid-catalyzed hydration by a factor of 2200, and consequently the acid-catalyzed reaction of this, and other aromatic ketenes as well, becomes apparent only under strongly acidic conditions. Keywords: mesitylketene, ketene hydration, acid catalysis, Cox–Yates excess acidity correlation.

Thermal properties of aminopolycarboxylic acid solutions in the temperature range 20–80°C

The thermal properties (thermal conductivity, thermal diffusivity, and volumetric heat capacity) of aminopolycarboxylic acids, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diet hylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), 1,2-diaminocyclohexanetetraacetic acid (DCTA), and ethyleneglycol-bis-(2-aminoethylether) tetraacetic acid (EGTA), in dilute solutions of sodium hydroxide were measured in the temperature range 20–80°C. The measurements were performed with a hot-wire (strip) technique. The results show that the values of the thermal properties depend on the number of nitrogen atoms and the number of carboxyalkyl groups, which are bounded to the nitrogen atom, of the aminopolycarboxylic acid and also on the concentration of the investigated compounds in the medium and the temperatures. The mechanism of heat transfer is discussed and the role of convection is taken into consideration.

Kinetics of the enolisation reactions of 2-acetylpyrrole and of 2-, 4- and 5-acetylthiazoles

Kinetic results are reported on the rates of enolisation of title compounds in water, in acetate buffers, in dilute hydrochloric acid, in dilute sodium hydroxide solutions and in the presence of several metal-ion salts, as measured by their rates of halogenation at 25°C. The results have been compared with those previously obtained from the corresponding reactions of acetophenone and a number of acetylheterocycles. It is shown that a suitable metal cation (e.g., Cu2+) can be hundreds of times more effective than the proton in catalysing the enolisation process of an acetylheterocyclic compound. This can be due either to the ‘soft’ character of the acetyl group, as, for example, that of 2-acetylpyrrole, or to coordination of both the carbonyl oxygen and the heteroatom by the metal cation in the transition state of the reaction, as for 2- and 4-acetylthiazoles.

A flash photolytic investigation of the photosolvolysis of α-(2,6-dimethoxyphenyl)vinyl chloride. Characterization of the 2,6-dimethoxyacetophenone keto–enol system

Photosolvolysis of α-(2,6-dimethoxyphenyl)vinyl chloride in trifluoroethanol solution at 25 °C was found to produce the α-(2,6-dimethoxyphenyl)vinyl cation as a transient species with the lifetime τ = 1 μs. Addition of water reduced this lifetime markedly, until, at compositions greater than 80% water, it was too short to measure (τ &lt; 20 ns); extrapolation of the data suggests τ = 9 ns in pure water. Hydration of this cation gave the much longer lived enol of 2,6-dimethoxyacetophenone, whose rates of ketonization were measured in dilute perchloric acid and sodium hydroxide solutions. These data, when combined with rates of enolization of the ketone determined by iodine scavenging, give pKE = 6.98 for the keto–enol equilibrium constant in the 2,6-dimethoxyacetophenone system, [Formula: see text] for the acidity constant of the enol ionizing as an oxygen acid, and [Formula: see text] for the acidity constant of the ketone ionizing as a carbon acid; these constants refer to wholly aqueous solution at 25 °C and ionic strength = 0.10 M.

Electrodialysis for clean-up of strongly alkaline samples in ion chromatography

An electrodialysis method is described for the off-line neutralization of strongly alkaline samples containing trace levels of common inorganic anions. This method uses an electrodialysis cell comprising three compartments separated from each other by cation-exchange membranes. These compartments comprise an anode compartment housing, a platinum wire anode and 10 ml of a suitable hydrogen ion donating medium, a sample compartment which contains 1 ml of the alkaline sample, and a cathode compartment housing a platinum wire cathode and a dilute solution of sodium hydroxide. During electrodialysis at either constant applied current or constant applied power, hydrogen ions from the anode compartment displace sodium ions from the sample, thereby effecting neutralization. Experimental parameters, such as the magnitude of the applied current or power, the type of cation-exchange membrane used and the design of the cell have been studied and optimum results were obtained using a Neosepta CM-2 membrane, of area 616 mm 2 supported between two perspex discs, with an applied current of 150 mA or applied power of 3 W. Under these conditions, a 1 ml sample of 1 M sodium hydroxide could be neutralized in 11 min. The most effective hydrogen ion donating medium consisted of a 2:1 (w/v) slurry of BioRad AG 50W-X8 (200–400 mesh, H + form) cation-exchange resin in 1 m M octanesulfonic acid. Recoveries of solute anions (3–10 μg/ml) from the dialysed solution were close to quantitative, except for fluoride and nitrite, which gave recoveries of less than 60%. It is suggested that low recoveries for these ions are due to formation of neutral, protonated species within the membrane with subsequent loss by diffusion.