Aqueous NaHCO3 Research Articles

Determination of benzoic acid in milk by solid-phase extraction and ion chromatography with conductivity detection

A simple, fast, precise and eco-friendly method, based on ion chromatography (IC) with a suppressed conductivity detector, was proposed for the determination of benzoic acid (BA) in milk in this paper. The chromatographic separation was accomplished by using an anion exchange column eluted with 3.2 mmol/L aqueous Na2CO3 and 1.0 mmol/L aqueous NaHCO3 at a flow-rate of 0.7 mL/min. The method validation experiment provided excellent results with respect to linearity (correlation coefficient up to 0.9997), limit of detection (0.1 μg/L), recovery values (ranging from 88.0% to 93.0%) and relative standard deviation (RSD) (below 2.2%, n = 7).

The effect of NaHCO3 treatment time on the corrosion resistance of commercial magnesium alloys AZ31 and AZ61 in 0.6 M NaCl solution

This paper studies the chemical composition and structure of the conversion coatings formed during immersion on saturated aqueous NaHCO3 solution treatment on the surface of as-received commercial AZ31 and AZ61 magnesium alloys with a view to a better understanding of their protective properties. The great uniformity and the significant increase in the amount of aluminium oxides and hydroxides observed on the surface of the conversion coating of the AZ61 alloy after 10 or 60min of treatment (about 30% higher Al atomic contents) seems to improve the corrosion resistance.

Electrochemical reduction of CO2 over Sn-Nafion® coated electrode for a fuel-cell-like device

Commercially available Sn particles mixed with Nafion® ionomer are used to prepare an electrode with a gas diffusion layer support in a manner similar to that in which fuel cell electrodes are prepared. Cyclic voltammetry is performed in aqueous NaHCO3 (basic medium) on the electrode and the Tafel parameters are obtained and compared with a Sn metal disc and with a graphite disc coated with Sn powder. In addition, electrolysis is carried out potentiostatically, also in NaHCO3 solution, at various potentials. The exchange current density on the Sn/gas diffusion layer electrode shows to be two orders of magnitude higher that on the metallic Sn disc. The maximum current density obtained during electrolysis is 27 mA cm−2 at −1.6 V vs. NHE, with 70% faradaic efficiency towards the formation of formate, which is one of the highest values found in the literature on Sn electrode at ambient pressure.

Instability of pressure driven viscous fluid streams in a microchannel under a normal electric field

This paper investigates analytically and experimentally electrohydrodynamic instability of the interface between two viscous fluids with different electrical properties under constant flow rates in a microchannel. In the three-dimensional analytical model, the two-layer system is subjected to an electric field normal to the interface between the two fluids. There is no assumption on the magnitude of the ratio of fluid to electric time scales, and thus the linear Poisson–Boltzmann equation are solved using separation of variable method for densities of bulk charge and surface charge. The electric field and fluid dynamics are coupled only at the interface through the tangential and normal interfacial stress balance equations. In the experiments, two immiscible fluids, aqueous NaHCO3 (the high electrical mobility fluid) and silicone oil (polydimethylsiloxane, the low electrical mobility fluid) are pumped into a microchannel made in polymethyl methacrylate) (PMMA) substrate. The normal electric field is added using a high voltage power supply. The results showed that the external electric field and increasing width of microchannel destabilize the interface between the immiscible fluids. At the same time, the viscosity of the high electrical mobility fluid and flow rates of fluids has a stabilizing effect. The experimental results and the analytical results show a reasonable agreement.

Direct Nanoscale Observations of CO2 Sequestration during Brucite [Mg(OH)2] Dissolution

The dissolution and carbonation of brucite on (001) cleavage surfaces was investigated in a series of in situ and ex situ atomic force microscopy (AFM) experiments at varying pH (2-12), temperature (23-40 °C), aqueous NaHCO(3) concentration (10(-5)-1 M), and PCO(2) (0-1 atm). Dissolution rates increased with decreasing pH and increasing NaHCO(3) concentration. Simultaneously with dissolution of brucite, the growth of a Mg-carbonate phase (probably dypingite) was directly observed. In NaHCO(3) solutions (pH 7.2-9.3,), precipitation of Mg-carbonates was limited. Enhanced precipitation was, however, observed in acidified NaHCO(3) solutions (pH 5, DIC ≈ 25.5 mM) and in solutions that were equilibrated under a CO(2) atmosphere (pH 4, DIC ≈ 25.2 mM). Nucleation predominantly occurred in areas of high dissolution such as deep step edges suggesting that the carbonation reaction is locally diffusion-transport controlled. More extensive particle growth was also observed after ex situ experiments lasting for several hours. This AFM study contributes to an improved understanding of the mechanism of aqueous brucite carbonation at low temperature and pressure conditions and has implications for carbonation reactions in general.

Electrohydrodynamic and Shear-Stress Interfacial Instability of Two Streaming Viscous Liquid Inside a Microchannel for Tangential Electric Fields

The electrohydrodynamic and stress instability of the interface between two viscous fluids with different electrical properties under tangential electric fields in a microchannel is analytically and experimentally investigated. In the analytical model, the two-layer system is subjected to a tangential electric field. There is no assumption on the magnitude of the ratio of fluid to electric time scales, and thus the linear Poisson-Boltzmann equation are solved using separation of variable method for densities of bulk charge and surface charge; the electric field and fluid dynamic are coupled only at the interface through the stress balance equations. Under constant flowrates, the fractions of the fluids are calculated for different parameters. Using the calculated fractions, the stability of the system can be determined according to the linear perturbation theory. In the experiments, two immiscible fluids, aqueous NaHCO3 (conducting fluid) and silicone oil (non-conducting fluid) are pumped into a PMMA microchannel. The tangential electric field is added to the aqueous NaHCO3 using a high voltage power supply. The results are recorded using a CCD camera. The results show that the electric field can have either destabilizing or stabilizing effect depending on the ratios of viscosity of the two fluids. The flowrates, zeta potential, and dimension of the microchannel affect the growth rate of the perturbation. Both experimental and analytical results show a good agreement. Keywords: Interface, constant flowrate, linear instability, microchannel, TAS, conducting fluid, electroosmotic flow, VALIDATION, Viscosity

Tin Oxide Dependence of the CO2 Reduction Efficiency on Tin Electrodes and Enhanced Activity for Tin/Tin Oxide Thin-Film Catalysts

The importance of tin oxide (SnO(x)) to the efficiency of CO(2) reduction on Sn was evaluated by comparing the activity of Sn electrodes that had been subjected to different pre-electrolysis treatments. In aqueous NaHCO(3) solution saturated with CO(2), a Sn electrode with a native SnO(x) layer exhibited potential-dependent CO(2) reduction activity consistent with previously reported activity. In contrast, an electrode etched to expose fresh Sn(0) surface exhibited higher overall current densities but almost exclusive H(2) evolution over the entire 0.5 V range of potentials examined. Subsequently, a thin-film catalyst was prepared by simultaneous electrodeposition of Sn(0) and SnO(x) on a Ti electrode. This catalyst exhibited up to 8-fold higher partial current density and 4-fold higher faradaic efficiency for CO(2) reduction than a Sn electrode with a native SnO(x) layer. Our results implicate the participation of SnO(x) in the CO(2) reduction pathway on Sn electrodes and suggest that metal/metal oxide composite materials are promising catalysts for sustainable fuel synthesis.

Voltammetric probing of pH at carbon nanofiber–Nafion™–carbon nanofiber membrane electrode assemblies

Methods are developed for using a carbon nanofiber membrane electrode assembly (cnMEA) for three-electrode electrochemical measurements in unsupported liquid or gaseous media. The carbon nanofiber membrane (ca. 20 μm thickness) is hot-pressed from both sides onto a Nafion™ ion conductor film (ca. 50 μm thickness). The resulting cnMEA is employed as both a counter electrode and working electrode (with an external SCE reference electrode) for the liquid phase oxidation of hydroquinone in (i) 0.5 M, (ii) 0.05 M, and (iii) 0.005 M aqueous NaHCO 3, and (iv) in pure demineralised water. Well-defined voltammetric responses are obtained and pH effects are investigated. A gas–salt (di-ammonium sulphate) contact between the cnMEA working electrode and SCE reference electrode is then employed in a gas flow system to obtain voltammetric responses in contact with a humidified gas (N 2, 80% relative humidity). Reversible redox cycling of entrapped hydroquinone is demonstrated and humidity and pH effects are observed. Ammonia gas effects on Faradaic currents are explored. Voltammetric measurements provide direct insight into the MEA processes and conditions.

Preparation and X-ray Crystal Study of Benziodoxaborole Derivatives: New Hypervalent Iodine Heterocycles

A series of heterocyclic compounds containing trivalent iodine, oxygen, and boron in a five-membered ring were prepared and structurally investigated by X-ray crystallography. 1-Chloro-4-fluoro-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol was synthesized by chlorination of 2-fluoro-6-iodophenylboronic acid followed by treatment of the intermediate iododichloride with water. 1-Acetoxy-4-fluoro-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol, 1-acetoxy-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol, and similar 1-substituted trifluoroacetate derivatives of benziodoxaborole were prepared the hypochlorite oxidation of 2-fluoro-6-iodophenylboronic acid or 2-iodophenylboronic acid in acetic or trifluoroacetic acid, respectively. 1-Acetoxy substituted benziodoxaborole can be further converted to the respective trifluoroacetate by treatment with trifluoroacetic acid or to the 1-hydroxy derivative by basic hydrolysis with aqueous NaHCO(3). X-ray structural studies of 1-chloro- and 1-trifluoroacetoxy substituted benziodoxaboroles 13, 17, and 18 have shown the presence of a planar five-membered heterocyclic ring with unusually short endocyclic I-O bond distance of 2.04-2.09 Å. Slow crystallization of 4-fluoro-1-trifluoroacetoxy-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol from methanol resulted in the formation of a tetrameric macrocyclic structure 21 resulting from self-assembly of the initially formed 4-fluoro-1,3-dimethoxy-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol. Structural parameters of the five-membered iodoxoborol ring, such as the planar geometry and the short B-O and O-I bonds lengths in 13, 17, and 18 compared to those in 21 and known benziodoxoles are indicative of partially aromatic character of this ring. Density functional theory (DFT) predicted NIST (0) and NIST (1) indexes for 1-chloro- and 1-trifluoroacetoxy substituted benziodoxaboroles, however, are indicative of significantly lower aromaticity compared to the classic aromatic systems.

Synthesis and antibacterial properties of new N4-acetylated hexahydro-2,7-dioxopyrido[2,3-f]quinoxaline-8-carboxylic acids

Direct interaction between 7-chloro-1-cyclopropyl-6-fluoro-8-nitro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid and primary α-amino acids (exemplified by glycine, alanine, and l-valine) in aqueous ethanolic NaHCO3 at 70–80°C for 24–72 h produced the respective N-(4-oxoquinolin-7-yl)-α-amino acids (6a–c). The latter derivatives underwent reductive lactamization upon treatment with Na2S2O4 in aqueous ethanol to afford moderate yields of the corresponding pyrido[2,3-f]quinoxaline-8-carboxylic acids (8a–c). Acetylation of 8a–c using acetyl chloride afforded N4-acetylated hexahydro-2,7-dioxopyrido[2,3-f]quinoxaline-8-carboxylic acids (9a–c). The structures, assigned to these new heterocyclic products, are supported by analytical and spectral data. The synthesized compounds (6a–c/9a–c) showed appreciable antibacterial activity as compared with ciprofloxacin.

Simultaneous determination of nine flavonoids in Polygonum hydropiper L. samples using nanomagnetic powder three-phase hollow fibre-based liquid-phase microextraction combined with ultrahigh performance liquid chromatography–mass spectrometry

A simple, inexpensive, and efficient nanomagnetic powder three-phase hollow fibre-based liquid-phase microextraction (HF-LPME) technique combined with ultrahigh performance liquid chromatography–mass spectrometry (UPLC–MS) was developed for the simultaneous analysis of nine flavonoids in Polygonum hydropiper L. samples. The final, optimised extraction conditions were as follows: an organic solvent of ethyl acetate, a donor phase of aqueous KH 2PO 4 at pH 3.0, an acceptor phase of aqueous NaHCO 3 at pH 8.5, a stirring rate of 1000 rpm, and an extraction time of 50 min. Under these conditions, analyte calibration curves were all linear, with correlation coefficients ≥0.9994. The relative standard deviation for all analytes in intra-day (0.8–2.2%) and inter-day (1.7–3.5%) precision tests was well within the acceptable ranges, as were the limits of quantitation (LOQ < 0.054 μg/L) and detection (LOD < 0.170 μg/L). Recoveries for all standard compounds were between 95.17% and 99.82%, with a RSD of no more than 2.3%. Correlative analyses demonstrated that the physicochemical parameters of the compounds themselves also influenced the extraction efficiency. This technology proved to be rapid, sensitive, and reliable for the quality control of P. hydropiper L. samples.

In situ soft X-ray absorption spectroscopy investigation of electrochemical corrosion of copper in aqueous NaHCO 3 solution

A novel electrochemical setup has been developed for soft X-ray absorption studies of the electronic structure of electrode materials during electrochemical cycling. In this communication we illustrate the operation of the cell with a study of the corrosion behavior of copper in aqueous NaHCO 3 solution via the electrochemically induced changes of its electronic structure. This development opens the way for in situ investigations of electrochemical processes, photovoltaics, batteries, fuel cells, water splitting, corrosion, electrodeposition, and a variety of important biological processes.

Reaction of Dess–Martin periodinane with 2-(alkylselenyl)pyridines. Dehydration of primary alcohols under extraordinarily mild conditions

Dess–Martin periodinane oxidizes very rapidly 2-pyridylseleno derivatives RR′CHCH2SePy in CHCl3 or CH2Cl2 and more chemoselectively than mCPBA. Tetravalent selenanes, RR′CHCH2Se(OAc)2Py, seem to be formed. Treatment of these intermediates with aqueous NaHCO3 gives rise to irreversible hydrolysis and elimination to terminal alkenes. As the OH/SePy exchange can be performed in minutes, the overall process is an exceptionally efficient procedure for the dehydration of primary alcohols.

A New Arylsulfate Sulfotransferase Involved in Liponucleoside Antibiotic Biosynthesis in Streptomycetes

Sulfotransferases are involved in a variety of physiological processes and typically use 3'-phosphoadenosine 5'-phosphosulfate (PAPS) as the sulfate donor substrate. In contrast, microbial arylsulfate sulfotransferases (ASSTs) are PAPS-independent and utilize arylsulfates as sulfate donors. Yet, their genuine acceptor substrates are unknown. In this study we demonstrate that Cpz4 from Streptomyces sp. MK730-62F2 is an ASST-type sulfotransferase responsible for the formation of sulfated liponucleoside antibiotics. Gene deletion mutants showed that cpz4 is required for the production of sulfated caprazamycin derivatives. Cloning, overproduction, and purification of Cpz4 resulted in a 58-kDa soluble protein. The enzyme catalyzed the transfer of a sulfate group from p-nitrophenol sulfate (K(m) 48.1 microM, k(cat) 0.14 s(-1)) and methyl umbelliferone sulfate (K(m) 34.5 microM, k(cat) 0.15 s(-1)) onto phenol (K(m) 25.9 and 29.7 mM, respectively). The Cpz4 reaction proceeds by a ping pong bi-bi mechanism. Several structural analogs of intermediates of the caprazamycin biosynthetic pathway were synthesized and tested as substrates of Cpz4. Des-N-methyl-acyl-caprazol was converted with highest efficiency 100 times faster than phenol. The fatty acyl side chain and the uridyl moiety seem to be important for substrate recognition by Cpz4. Liponucleosides, partially purified from various mutant strains, were readily sulfated by Cpz4 using p-nitrophenol sulfate. No product formation could be observed with PAPS as the donor substrate. Sequence homology of Cpz4 to the previously examined ASSTs is low. However, numerous orthologs are encoded in microbial genomes and represent interesting subjects for future investigations.

Graphite‐Supported Gold Nanoparticles as Efficient Catalyst for Aerobic Oxidation of Benzylic Amines to Imines and N‐Substituted 1,2,3,4‐Tetrahydroisoquinolines to Amides: Synthetic Applications and Mechanistic Study

Selective oxidation of amines using oxygen as terminal oxidant is an important area in green chemistry. In this work, we describe the use of graphite-supported gold nanoparticles (AuNPs/C) to catalyze aerobic oxidation of cyclic and acyclic benzylic amines to the corresponding imines with moderate-to-excellent substrate conversions (43-100%) and product yields (66-99%) (19 examples). Oxidation of N-substituted 1,2,3,4-tetrahydroisoquinolines in the presence of aqueous NaHCO3 solution gave the corresponding amides in good yields (83-93%) with high selectivity (up to amide/enamide=93:4) (6 examples). The same protocol can be applied to the synthesis of benzimidazoles from the reaction of o-phenylenediamines with benzaldehydes under aerobic conditions (8 examples). By simple centrifugation, AuNPs/C can be recovered and reused for ten consecutive runs for the oxidation of dibenzylamine to N-benzylidene(phenyl)methanamine without significant loss of catalytic activity and selectivity. This protocol "AuNPs/C+O2" can be scaled to the gram scale, and 8.9 g (84 % isolated yield) of 3,4-dihydroisoquinoline can be obtained from the oxidation of 10 g 1,2,3,4-tetrahydroisoquinoline in a one-pot reaction. Based on the results of kinetic studies, radical traps experiment, and Hammett plot, a mechanism involving the hydrogen-transfer reaction from amine to metal and oxidation of M-H is proposed.

The Removal of Copper Ions from Aqueous Solution Using Phosphoric Acid Modified β- Zeolites

An attempt was made to modify zeolite so as to find use as ion-exchange material for the removal of copper ion from industrial wastewaters. Large pore Hβ zeolite was initially modified with phosphoric acid and further treated with aqueous NaHCO 3 solution to obtain the PNa 2 -β. The prepared PNa 2 - β was characterized by XRD, BET Surface area, SEM and AAS techniques. The sorptive removal of copper ion from aqueous solutions using modified - β zeolites was investigated. The PNa 2 - β zeolite showed higher sorption capacity than Na- β zeolite. It is because of the exchangeable Na + ions being doubled in the PNa 2 - β compared to the Na- β zeolite. Equilibrium data were fitted to linear Langmuir and Freundlich models while the kinetic data were represented by pseudo-first order and pseudosecond order kinetic models.

Removal of Nickel(II) from Aqueous Solutions by Adsorption with Modified ZSM‐ 5 Zeolites

The sorptive removal of nickel ion from aqueous solutions using modified ZSM‐5 zeolites was investigated. Experiments were carried out as a function of solute concentration and different temperatures. Mesoporous material of ZSM‐5 zeolite was modified with phosphoric acid by wet method. The modified zeolite was converted to Na+ form using aqueous NaHCO3 solution. The Na+ form of modified zeolite, represented as PNa2-‐ZSM‐5 was characterized by XRD, BET, SEM and AAS techniques. It was then tested for ion exchange with aqueous Ni(SO4) solution. The Ni2+ content of the solution was analyzed by AAS. Phosphoric acid modified PNa2-‐ZSM‐5 zeolite shows higher adsorption capacity than the parent Na‐Y zeolite. Equilibrium modeling data were fit to linear Langmuir model then the Freundlich model. These parameter confirmed that sorption of Ni2+ is feasible spontaneous and endothermic.

Simple high-performance liquid chromatography—fluorescence detection method for plasma, kidney and liver of rat as a tool for toxicology studies

A fast and simple HPLC-FLD (high-performance liquid chromatography-fluorescence detection) analytical method has been developed and validated for the determination of ochratoxin A in rat plasma, kidney and liver. The extraction method, calibration curves and chromatographic conditions are common for the three matrices. Plasma and homogenized tissue samples (250 μL) were extracted with ethanol (400 μL) and trichloroacetic acid 20% (w/v) (50 μL). Supernatants were directly injected into the HPLC system, analyzed on a 5-μm (25 cm × 0.4 cm) Tracer Extrasil ODS2 column using FLD (excitation wavelength = 225 nm, emission wavelength = 461 nm). The mobile phase was 29:29:42 (v/v) methanol–acetonitrile–sodium acetate. The small volume of sample needed which allows the obtaining of ochratoxin A levels in individual tissue samples from small animals and the wide range of concentrations that could be analyzed make this method easy to apply in toxicology and toxicokinetic studies of this mycotoxin, even in low dose carcinogenic studies. This method was linear and selective for all the matrices. Precision and accuracy were always <10% and recovery was very efficient in each case. Limits of detection and quantification were also calculated in plasma (1 and 8.4 μg/L), kidney (14.3 and 55.8 μg/kg) and liver (4.1 and 52.8 μg/kg). Stability of the tissue homogenates was assured for at least 10 months at −80 °C. The method has been successfully applied to the analysis of rat samples after 7 days of ochratoxin A (0.5 mg/kg b.w. dissolved in an aqueous NaHCO 3 solution) administration by oral gavage.

Exploring the reaction of iodine with α‐diazo esters

AbstractIn this paper we describe the unprecedented reaction between α‐diazo esters 1 and iodine. The reaction, carried out in the presence of aqueous NaHCO3, afforded the Z‐isomer of the corresponding unsaturated‐2‐iodo ester 8. The configuration of compounds 8 was determined using the 3JCH coupling between carbonyl carbon atom and alkene proton. Mechanistic considerations accounting for the observed phenomena and including quantum chemical calculations are proposed. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Phosphoric acid modified-Y zeolites: A novel, efficient and versatile ion exchanger

Large pore HY zeolite was modified with phosphoric acid by wet method. The modified zeolite was converted to Na + form using aqueous NaHCO 3 solution . The Na + form of modified zeolite, represented as PNa 2Y, was characterized by XRD, BET surface area, SEM, and AAS techniques. The XRD analysis showed diffraction patterns same as that of parent HY zeolite, as a result there has been no structural degradation during modification. It was then tested for sorption of Cu 2+ ions from aqueous solution. The Cu 2+ content of the solution was analyzed by AAS. PNa 2-Y shows higher sorption capacity (≈40%) than the parent Na-Y (≈23%) zeolite, which is attributed to the double of amount Na + content in PNa 2-Y compared to the Na-Y zeolite. Equilibrium modeling data were found to fit more to the linear Langmuir model than the Freundlich model. The thermodynamic parameters such as change in free energy (Δ G°), enthalpy (Δ H°), and entropy (Δ S°), were also calculated. These parameters confirmed that the sorption of Cu 2+ is feasible, spontaneous and endothermic.