Sodium Borohydride Concentration Research Articles

Novel Silica Based Coatings as a Substitute for Chrome Passivates

A novel electroless method was developed to deposit corrosion resistant silica coatings. Process parameters such as bath temperature, concentration of sodium silicate and sodium borohydride were optimized based on the uniformity and corrosion resistance of the final deposit obtained. Accelerated corrosion tests as per ASTM B117 standards show corrosion performance comparable to that of chrome passivates.

Synthesis, Characterization, and Tunable Optical Properties of Hollow Gold Nanospheres

Nearly monodisperse hollow gold nanospheres (HGNs) with tunable interior and exterior diameters have been synthesized by sacrificial galvanic replacement of cobalt nanoparticles. It is possible to tune the peak of the surface plasmon band absorption between 550 and 820 nm by carefully controlling particle size and wall thickness. Cobalt particle size is tunable by simultaneously changing the concentration of sodium borohydride and sodium citrate, the reducing and capping agent, respectively. The thickness of the gold shell can be varied by carefully controlling the addition of gold salt. With successful demonstration of ensemble as well as single HGN surface-enhanced Raman scattering, these HGNs have shown great potential for chemical and biological sensing applications, especially those requiring nanostructures with near-IR absorption.

Application of a wall-stabilized argon plasma arc for the determination of some volatile hydride-forming elements

Volatile hydrides of As, Se, Sb and Sn, produced by a continuous manifold hydride generator, have been swept with argon and injected into the plasma of home-made direct current wall-stabilized argon plasma arc via one of its stabilizing segments. The arc burns in argon with an arc current of 20 A and a cathode-anode voltage of 40 V. Measurements were carried out using a 1 m focal length computer-controlled monochromator (Jobin Yvon 1000R) equipped with a holographic grating having 2400 grooves mm − 1 . Optimal values of the experimental variables that give the highest value of intensity ratio of line-to-background were determined. These are: plasma gas flow rate 1.0 l min − 1 , carrier gas flow rate 0.35 l min − 1 for As and Sb and 0.6 l min − 1 for Se and Sn, concentration of nitric acid used for acidification of the sample 2 M for As and Sb, 0.5 M for Se and 0.1 M for Sn and sodium borohydride concentration: 1.5% for As and Se and 2% for Sb and Sn. Chemical interference of some transition elements that affect the hydride generation process and a trial to mask their interference effect were investigated. Calibration curves were linear and limits of detection calculated on the base of 3 σ of the background were found to be as low as 3.9, 6.8, 9.8 and 13.2 ng ml − 1 for As, Se, Sb and Sn, respectively. Finally, the analytical applicability of the arc device was tested by the determination of As in four lake sediment samples, LKSD 1, LKSD 2, LKSD 3 and LKSD 4, of the Centre for Mineral and Energy Technology, Ottawa, Ontario, Canada, which have been analyzed for As using atomic absorption spectrometry (AAS). The results were in good agreement with those obtained by AAS.

Novelties of kinetics of chemoselective reduction of citronellal to citronellol by sodium borohydride under liquid–liquid phase transfer catalysis

Borohydride reductions, although common, have not been studied from kinetic and mechanistic view points due to complex chemistry and more so, there is no report on kinetics and mechanism of such reductions under phase transfer catalysis. The novelties of phase transfer catalysed chemoselective reduction of citronellal to citronellol using sodium borohydride were studied in detail in liquid–liquid phase transfer catalysis using tetrabutylammonium bromide (TBAB), tetrapropylammonium bromide (TPAB), tetraethyl ammonium bromide (TEAB) and tetrabutylammonium hydrogen sulfate (TBAHS). TBAB was the best catalyst at 30 °C. Citronellol is very extensively used in a number of perfume compositions. The effects of different parameters such as speed of agitation, phase volume ratio, catalyst concentration, sodium borohydride concentration, citronellal concentration and temperature have been studied. The reaction was found to be 100% selective towards the formation of the desired product. The kinetics and mechanism are presented to account for the effects of various parameters on conversion and rates. It was possible to establish both rate constant and distribution constant from the same set of data. The results are novel.

Formation of electroless Ni–B coatings using low temperature bath and evaluation of their characteristic properties

The formation of electroless Ni–B coatings obtained using a low temperature bath and evaluation of their characteristic properties are addressed in this paper. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni–B coatings. The influence of concentration of sodium borohydride in bath on the plating rate and the nickel/boron content of the resultant Ni–B coatings was studied. Selected coatings were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively, for assessing the phase content, phase transformation behaviour and magnetic properties. XRD patterns reveal that the structure of electroless Ni–B coatings in as-plated condition is a function of the boron content of the coating: higher the boron content, greater the amorphous nature of the coating and vice-versa. DSC traces exhibit two exothermic peaks around 300 and 420 °C, corresponding to the phase transformation of crystalline nickel and Ni 3B phases at 300 °C and the transformation of a higher phase compound to Ni 3B at 420 °C. VSM studies indicate that the magnetic properties of the coating is also a function of the boron content of the coating: higher the boron content, lesser the saturation magnetization.

Synthesis of Pt–Ru nanoparticles with a bifunctional stabilizer

A synthetic method for bimetallic Pt–Ru nanoparticles with a bifunctional stabilizer, (3-aminopropyl)trimethoxysilane (APS), is proposed. Sodium borohydride was used to induce simultaneous reduction of platinum and ruthenium ions in the presence of APS. The concentration of each metal ion was 0.06 mM, and sodium borohydride concentration was 10 times higher than the total metal ion concentration. X-ray diffraction measurement showed that the nanoparticles formed by the reduction contained alloy of Pt and Ru. Comparison of the Pt–Ru nanoparticles prepared in the presence of APS with those in the absence of APS confirmed that APS played a role of stabilizer in synthesis of the nanoparticles. The number-averaged size of Pt–Ru nanoparticles could be varied in the range of 2.1–3.7 nm at APS concentrations of 0.13–0.26 mM, and the narrowest size distribution of Pt–Ru nanoparticles appeared with the minimum average size (2.1 nm) around an APS concentration of 0.1 mM.

Optimization of penicillin G acylase multipoint immobilization on to glutaraldehyde-chitosan beads.

The objective of this work was to study the immobilization of penicillin G acylase from Escherichia coli on to chitosan-glutaraldehyde beads by multipoint covalent binding. This process was optimized using a 2(3) experimental design. The parameters selected for the present study were the concentrations of glutaraldehyde, phenylacetic acid and sodium borohydride. Three responses were chosen, namely immobilization yield and stabilization factors of enzyme derivatives at high temperature and at alkaline pH. All the runs at the maximum (+1) and minimum (-1) levels were performed at random. Three experiments were performed at the centre point, coded as zero, for experimental-error estimation. With respect to immobilization yield, the main effectors were the concentrations of glutaraldehyde and phenylacetic acid. For stabilization factors at 50 degrees C and at alkaline pH, the main effectors were the concentrations of glutaraldehyde and sodium borohydride and the interaction between them.

Effect of experimentally induced reducing conditions on the mobility of arsenic from a mining soil

A method for estimating the release of contaminants from contaminated sites under reducing conditions is proposed. The ability of two chemical reducing agents, sodium ascorbate and sodium borohydride, to produce different redox environments in a gold mining soil contaminated with arsenic was investigated. Liquid–solid partitioning experiments were carried out in the presence of each of the reducing agents at different pH conditions. Both the effect of varying concentrations of the reducing agent and the effect of varying pH in the presence of a constant concentration of the reducing agent were studied. Concentrations of sodium ascorbate ranging from 0.0075 to 0.046 mol L −1 and concentrations of sodium borohydride ranging from 0.0075 to 0.075 mol L −1 were examined. The addition of varying concentrations of sodium borohydride provided greater reducing conditions (ranging from −500 to +140 mV versus NHE) than that obtained using sodium ascorbate (ranging from −7 to +345 mV versus NHE). The solubilization of arsenic and iron was significantly increased by the addition of sodium ascorbate for all concentrations examined and pH tested, compared to that obtained under oxidizing conditions (as much as three orders of magnitude and four orders of magnitude, respectively, for the addition of 0.046 mol L −1 of sodium ascorbate). In contrast, the alkaline and highly reduced soil conditions obtained with sodium borohydride lead to a lower effect on arsenic solubilization (as much as one order of magnitude for pH values between ca. 7 and 10 and no effect for pH values between ca. 10 and 12) and no effect on iron solubilization for all concentrations examined and pH tested. At similar ORP–pH conditions the results of extraction for arsenic and iron were different for the two reagents used.

Evaluation of two flow injection systems for mercury speciation analysis in fish tissue samples by slurry sampling cold vapor atomic absorption spectrometry

Two simple flow injection (FI) systems were used for mercury speciation analysis in slurried fish tissue samples by cold vapor-atomic absorption spectrometry (CV-AAS). The solid samples were first suspended in hydrochloric acid containing Triton X-100 as dispersing agent, and then the slurries were injected in an acid carrier stream, which was either sequentially mixed with sulfuric acid, potassium persulfate oxidizing agent and stannous chloride reducing agent streams or merged with sodium borohydride reducing agent stream. Mercury speciation analysis was carried out as function of the oxidation coil temperature or sodium borohydride concentration, respectively. The detection limit of the method was 57 and 67 ng g−1, referred to dry weight, using the FI system with on-line oxidation for inorganic mercury and total mercury determination, respectively. Nevertheless, the FI system without on-line oxidation resulted in being simpler, faster and more sensitive for inorganic mercury and total mercury determination. Furthermore, the last system permitted the separate determination of methylmercury and inorganic mercury by selecting an adequate hydrochloric acid concentration in the suspension medium and the suitable sodium borohydride reducing agent. The detection limit of the method was 4.04, 0.977 and 11.0 ng g−1, referred to dry weight, for total mercury, inorganic mercury and methylmercury determination, respectively. Both FI methodologies were validated using two fish tissue certified reference materials, NRC DOLT-2 and NRC DORM-2, obtaining results in good agreement with the certified values, and were applied to the analysis of two real mussel tissue samples.

Arsenic and antimony determination by on-line flow hydride generation–glow discharge–optical emission detection

Hollow cathode (HC) and conventional flat cathode (FC) glow discharge (GD) optical emission spectrometry (OES) were used as detectors for the determination of arsenic and antimony by on-line hydride generation (HG) in a flow system. Both radiofrequency (rf) and direct current (dc) sources were investigated to produce the discharge. The design of the HC and FC and also the parameters governing the discharge (pressure, He flow rate, voltage, current and delivered power) and the HG (sodium borohydride concentration and reagent flow rates) were investigated using both cathodes. The analytical performance characteristics of HG–GD–OES with HC and FC were evaluated for some emission lines of arsenic (193.7, 200.3, 228.8 and 234.9 nm). The best detection limit (0.2 μg l −1) was obtained when the emission line of 228.8 nm was used with FC. Under the same arsenic optimized experimental conditions, the system was evaluated to determine antimony at 259.7, 252.7 and 231.1 nm, 252.7 nm being the emission line which produced the best detection limit (0.7 μg l −1). The rf-HC–GD–OES system was applied successfully to the determination of arsenic in freeze-dried urine in the standard reference material 2670 from NIST. Finally, a flow injection system was assayed to determine arsenic at 228.8 nm, using a dc-GD with both FC and HC. The results indicated that for low volumes of sample, the HC discharge allows better analytical signals than the FC.

ダイレクトメタリゼーション法による導電性微粒子の作製

A new conducting method of ultrafine polymer particles by using direct metallization technology was proposed in this paper. Carboxyl groups, as a cation exchange group, were formed onto the particle surfaces through NaOH hydrolysis treatment. Nickel ions absorbed to the cation exchange groups were reduced by sodium borohydride. Size of metal nickel nuclei after the reduction treatment depended on pH, particle concentration, and sodium borohydride concentration. In an acid solution, minute metal nickel nuclei deposited on the particle surfaces. Subsequent electroless Ni-P plating could form complete Ni films on the surfaces of particles reduced in the acid solution.

The reaction mechanism of DNA glycosylase/AP lyases at abasic sites.

DNA glycosylase and glycosylase/abasic (AP) lyases are the enzymes responsible for initiating the base excision repair pathway by recognizing the damaged target base and catalyzing the breakage of the base-sugar glycosyl bond. The subset of glycosylases that have an associated AP lyase activity also catalyze DNA strand breakage at the resulting or preexisting AP site via a beta-elimination reaction, proceeding from an enzyme-DNA imino intermediate. Two distinct mechanisms have been proposed for the formation of this intermediate. These mechanisms essentially differ in the nature of the first bond broken and the timing of the opening of the deoxyribose ring. The data presented here demonstrate that the combined rate of sugar ring opening and reduction of the sugar is significantly slower than the rate of formation of a T4-pyrimidine dimer glycosylase (T4-pdg)-DNA intermediate. Using a methyl-deoxyribofuranose AP-site analogue that is incapable of undergoing sugar ring opening, it was demonstrated that the T4-pdg reaction can initiate at the ring-closed form, albeit at a drastically reduced rate. T4-pdg preferentially cleaved the beta-anomer of the methyl-deoxyribofuranose AP site analogue. This is consistent with a mechanism in which the methoxy group is backside-displaced by the amino group from the alpha-face of the deoxyribofuranose ring. In addition, studies examining rates of sugar-aldehyde reduction and the sodium borohydride concentration dependence of the rate of formation of the covalent imine intermediate suggest that the reduction of the intermediate is rate-limiting in the reaction.

Sodium borohydride reduction of aqueous iron–zirconium solutions: chemical routes to amorphous and nanocrystalline Fe–Zr–B alloys

Fine particle Fe–Zr–B alloys have been prepared by sodium borohydride reduction of aqueous solutions of iron(II) and zirconium(IV) sulfate. A comprehensive survey of reaction conditions was completed and optimum parameters found for the preparation of precipitated products. These included rapid stirring, controlled pH in the range 5–6, using degassed solvents, Fe∶Zr ratios between 4∶1 and 20∶1 and sodium borohydride concentrations between 0.1 and 1.2 M. Scanning electron microscopy showed that the products comprised spherical particles of 0.1 µm diameter with metal compositions, determined by atomic absorption, electron microprobe and EDAX, which mirrored the initial starting solutions. The products fell into two categories: amorphous Fe–Zr–B alloys when the Fe∶Zr ratio was near 9∶1, and nanocrystalline alloys, comprising a small amount of nanometre scale α-Fe crystallites embedded in amorphous Fe–Zr–B alloy, when the Fe∶Zr ratio was either higher or lower than 9∶1. Minor impurities in the form of Fe(II) complex and Fe(III) oxide phases were also detected in the products. Full structural and magnetic characterisations were performed on selected samples, including X-ray diffraction, Mossbauer spectroscopy, differential scanning calorimetry, magnetometry and Zr-edge EXAFS measurements.

Determination of organic lead in soils and waters by hydride generation inductively coupled plasma atomic emission spectrometry

This paper describes a simple and rapid method for the determination of the sum of tetraalkyllead (TAL) compounds (Me4Pb, Et4Pb) and their intermediate decomposition products, the trialkyllead (Me3Pb+, Et3Pb+) and dialkyllead (Me2Pb2+, Et2Pb2+) species.The lead species in solution are transformed into the corresponding hydrides by sodium tetrahydroborate and directly introduced into the ICP torch. Hydride generation takes place in a continuous flow hydride generator and the products are fed into an inductively coupled plasma atomic emission spectrometer. This arrangement avoids the necessity for solvent extraction and sample transfer. The reaction conditions (argon flow rate, concentration of acid and concentration of sodium borohydride) have been optimized. The acid is decisive for obtaining strongly different sensitivities for organic lead and inorganic lead; 2.0% (m/v) citric acid suppresses the signal of inorganic lead and this offers the possibility to determine the organolead compounds in the presence of excess amounts of inorganic lead, thus characterizing the method as a screening method. Linear calibration for six organolead compounds of varying polarity (neutral and ionic species) was established over the concentration range of 0.1 to 100µg l–1. Spiked natural water and soil samples were analyzed by this method with recoveries of 71–107%. Best extraction efficiences were found for a mixture of 5 ml of 1% ammonical methanol and 5 ml of 0.2 M sodium acetate. The optimized method was tested for soil samples with varying matrices and a wide range of concentrations of alkyllead obtained from an old industrial production site.

Behaviour of selenium compounds in FI-HG-AAS

The borohydride active volatile compound formation potential of twelve selenium compounds [selenous acid, selenic acid, selenocystine (Secys), selenohomocystine (Sehcys), selenomethionine (Semet), selenoethionine (Seet), trimethylselenonium iodide (TmSe), selenocystathionine (Secystha), selenocystamine (Secysta), selenourea (Seur), selenocholine (Sech), and dimethyl(3-amino-3- carboxy-1-propyl)selenonium iodide (DmpSe)] were investigated in a FI-HG system with different sodium borohydride concentrations (0.3% in 0.1% sodium hydroxide, and 0.5, 0.7, and 1.0% in 0.2% sodium hydroxide) in the presence of 3 M hydrochloric acid using an atomic absorption spectrometer as selenium-specific detector. Percentage recoveries with respect to selenous acid of selenic acid, Secys, Sehcys, Semet, Seet, TmSe, Secystha; Secysta, Seur, Sech, and DmpSe were 0, 10.3, 19.7, 23.5, 32.4, 13.7, 16.5, 16.5, 11.3, 5.6 and 7.7%, respectively in the presence of 0.3% borohydride stabilized with 0.1% sodium hydroxide. By multiplying the borohydride concentrations, percentage recoveries of TmSe, DmpSe, Sech, Sehcys and Secysta were elevated, whereas those of Semet, Seet and Seur were reduced. However, percentage recoveries of Secys and Secystha remained almost uniform within the entire borohydride range. TmSe exhibited a 105% recovery with respect to selenous acid at 1.0% borohydride concentration, whereas selenic acid was inert to borohydride active volatile compound formation.

Speciation of arsenic and selenium compounds by ion chromatography with inductively coupled plasma atomic emission spectrometry detection using the hydride technique

Different forms (species) of arsenic and selenium play an important role in biological and environmental samples. For example, arsenic is widely dispersed in the environment by emission of about 32 · 10 6 kg/year as a result of anthropological inputs. The feasibility of species and multi-element determinations after ion chromatographic separation was investigated using inductively coupled plasma atomic emission spectrometry (ICP-AES) as an atomic spectrometric detection technique. After the separation of arsenic(III), arsenic(V), dimethylarsinic acid and selenium(IV) on an ion-exchange column PRP X-100 with a mobile phase of 1 m M p-hydroxybenzoate—0.4 m M benzoate at pH 8.5 the analyte ions were transferred to the hydride forms. The analyte gas was separated from the aquatic phase by a laboratory-made low-volume gas—liquid separation chamber. With optimized reagent concentrations of sodium borohydride and hydrochloric acid the efficiency of the hydride generation of the investigated compounds is in the range of 85 to 96%. Compared with the pneumatic nebulization, the sensitivity was increased by a factor of 50 using on-line post-column hydride formation. In addition, the parameters of the plasma, e.g. plasma power, argon gas flows and emission lines were optimized to achieve a high sensitivity of the ICP detection. The comparison of the sensitivities and reproducibilities shows the improvement by ICP-AES detection.

Sensitive detection of ionic organolead compounds by coupling hydride generation (HG) with transversely heated graphite atomizer-atomic absorption spectrometry (THGA-AAS)

The detection of ionic alkyllead compounds using the coupling of flow injection analysis system-hydride generation (FIAS-HG) with transversely heated graphite atomizer atomic absorption spectrometry (THGA-AAS) has been worked out. Very low limits of detection can be achieved if the hydride products are enriched in the graphite furnace. Under optimised conditions (concentration of sodium borohydride, hydrogen peroxide and acidity as well as the furnace temperature) calibrations are carried out in the range of 0.1 to 5 μg/L. With a 1.5 mL sample loop, the limit of detection is calculated to be about 7 ng/L, but it can be lowered to below 1 ng/L if larger sample volumes are used for the enrichment.

High-performance liquid chromatographic determination of native and reduced α-glucan oligosaccharides on reversed phase columns using post-column immobilized enzyme reactors

A post-column enzyme reactor with co-immobilized glucoamylase and glucose oxidase has been used for the detection of α-glucans after HPLC separation of native and NaBH4-reduced oligosaccharides. Oligomers eluting from the column were cleaved into monomers which were oxidized with production of hydrogen peroxide, which was measured amperometrically at a platinum electrode. Detection of α-glucans proved to be highly selective and sensitive. The enzyme reactors are very stable under the conditions used. Linear calibration graphs were observed over 3 decades, and the detection limit for various oligosaccharides is into the lower ng range. Efficient separations were obtained on reversed phase columns using gradient elution with acetonitrile. Reduced oligomers were separated up to a degree of polymerization >40. The influence of temperature, pH, reaction time and sodium borohydride concentration was evaluated for the reduction of α-glucans. Reduction is complete within 2 minutes at 80°C and within 20 minutes at room temperature.

Precipitation of Metallic Platinum into Nafion Ionomer Membranes: I . Experimental Results

Extended x‐ray absorption fine structure (EXAFS) spectroscopy was used to investigate the precipitation of metallic platinum into Nafion ionomer membranes. First, x‐ray absorption spectra above the edge were obtained to compare the structure of platinum tetramine (i) solid, (ii) dissolved in water, and (iii) incorporated to Nafion sheets. The four amine groups remain linked to the platinum atom even after dissolution and incorporation into the membrane. EXAFS collected with dispersive optics was used to follow in situ the incorporation and the precipitation of the salt at edge. Time dependent concentrations of platinum salt in the membrane were obtained by measuring the time variation of the absorbance of the sample. The kinetics of incorporation were proportional to the salt concentration in the solution and depended on the hydrodynamic conditions at the interfaces. The precipitation was performed using a reducing solution of sodium borohydride. The chemical reduction of platinum tetramine into metallic platinum occurred directly without the formation of any stable intermediates. The kinetics of precipitation were proportional to the reducer concentration in the solution. After precipitation, concentration profiles of the metallic platinum across the membrane thickness were obtained by electron microprobe analysis. The concentration profiles in metallic platinum depend markedly upon (i) the sodium borohydride concentration in the solution, and (ii) the number of successive cycles of loading‐precipitation. The experimental data presented in this paper are employed to check the validity of two models developed for describing the two steps of ion‐exchange and precipitation.

Crown‐Ether Phase‐Transfer Catalysts for Reduction of Ketones, Oxidation of Olefins and Polymerization of p‐Xylenedibromide

AbstractVarious homogeneous and heterogeneous crown ether catalysts were prepared and applied as phase transfer catalysts for some reductions, oxidations and polymerizations. Among various crown ethers, 15‐crown‐5 seems the best to catalyze the reduction of ketones and aldehydes with sodium borohydride in nonpolar aprotic solvents. A granular entrapped 15‐crown‐5‐polyacrylamide catalysts was also prepared and applied as a heterogeneous catalyst for these reductions which seem to obey pseudo‐first‐order kinetics with rate constant 10−4–105 s−1. The steric effects of ketones and the effects of temperature and concentration of crown ethers, sodium borohydride and carbonyl compounds were also investigated. Among various crown ethers, 18‐crown‐6 is the best to catalyze the oxidation of olefins such as styrene, xylene and stilbene with potassium permanganate. Crown ethers were successfully applied as catalysts for anionic polymerization of p‐xylenedibromide with sodium dithionite as an initiator.