Phthalate Buffer Research Articles

Adsorption of Alginic Acid and Chondroitin Sulfate-A to Amine Functionality Introduced on Polychlorotrifluoroethylene and Glass Surfaces

The amine functionality is introduced onto a glass surface by using 3-(aminopropyl)-triethoxysilane (3-APTS)-a silane coupling agent-as well as by the adsorption of poly(L-lysine). The amine functionality is introduced onto the hydroxyl-functionalized polychlorotrifluoroethylene surface (PCTFE-OH) using 3-APTS as well. The amine-functionalized surfaces were thoroughly characterized by X-ray photoelectron spectroscopy (XPS). Selected polysaccharides, involved in fouling processes, such as alginic acid and chondroitin sulfate-A were allowed to adsorb onto amine-functionalized surfaces. It is shown that alginic acid adsorbs from calcium-free artificial seawater onto amine-functionalized glass surface prepared by the adsorption of poly(L-lysine) and onto amine-functionalized polychlorotrifluoroethylene surfaces (PCTFE-NH 2 ), The adsorption of alginic acid to PCTFE-NH 2 is very rapid, resulting in high-affinity isotherms and ∼5 A thick dry overlayer of the polysaccharide. In addition, we observe that the adsorbed alginic acid protects the PCTFE-NH 2 surface from hydrolysis by phosphate buffer 2 and from hydrolysis/oxidation by copper(II) acetate monohydrate solution. It is also shown that chondroitin sulfate-A adsorbs from potassium hydrogen phthalate buffer to the amine-functionalized glass surface prepared by the reaction between silanol groups on glass and 3-APTS. It is observed that alginic acid and chondroitin sulfate-A do not adsorb to the unmodified glass surface, which is polar and negatively charged, and the PCTFE surface, which is nonpolar, from aqueous solutions under various solution conditions. This study clearly indicates the importance of surface functional groups on the adsorption of polysaccharides, an important preliminary step in the biofouling of surfaces.

Spectrophotometric Determination of Enrofloxacin Through the Formation of a Binary Complex with Iron III, Ion-Pair and Charge-Transfer Complexation in Pure and Dosage Forms

Three simple and accurate spectrophotometric methods are described for the determination of enrofloxacin, a new fluoroquinolone synthetic orally active broad spectrum antibacterial. The first method is based on the reaction with iron III forming a water soluble yellow complex with maximum absorbance at 434 nm. The method allows the determination of 25–140 μgml−1. The second method involves ion-pair formation with bromocresol purple (BCP) in presence of phthalate buffer (pH 4.8±0.4). The yellow ion-pair is extracted with chloroform and the absorbance is measured at 410 nm. The method allows the determination of 4–18 μgml−1. The third method is based on the reaction of the drug with 8-dichloro-5,6 dicyano-p-benzoquinone (DDQ) in methanol as π-acceptor to give a molecular charge-transfer complex, with maximum absorbance at 460 nm. The method permits the determination of 50–240 μgml−1. Optimization of different experimental conditions were described. Beer's law was obeyed for the three methods and the relative standard deviation was found to be less than 2%. The methods have been applied successfully to the analysis of commercially available enrofloxacin preparations without interference from the ingredient commonly found.

Investigations on pitting corrosion of iron in perchlorate electrolytes

The pitting potential of iron in perchlorate solutions was measured in 1 M HClO 4, borate buffer (pH 9.3) and phthalate buffer (pH 5) both with additions of NaClO 4. A specifically designed electrochemical cell [1]has been used for in situ microscopic studies of the growth and geometry of pits caused by perchlorate ions. The growth rate and its dependence on the potential was determined by in situ and ex situ pulse measurements. Surface analytical studies with XPS showed a decomposition of the perchlorate ion during the pitting process. Additionally the critical pitting potential for iron in chlorate containing borate buffer solution was determined.

Comparison of the primary methods for pH measurement of the VNIIFTRI and the PTB

A comparison of the primary methods for pH measurement of Russia and Germany was carried out. Three buffer solutions: potassium tetraoxalate, 0.05 mol/kg, potassium hydrogen phthalate, 0.05 mol/kg and disodium tetraborate decahydrate, 0.01 mol/kg, prepared from materials of the All-Russian Research Institute for Physical, Technical and Radio-Technical Measurements (VNIIFTRI) and Merck KGaA, Germany, were used. The pH values obtained at 25 °C in this comparison agree within an expanded uncertainty of 0.004 for the borate and oxalate buffers and 0.005 for the phthalate buffer (k = 2).

Luminescence Lifetime Quenching of a Ruthenium(II) Polypyridyl Dye for Optical Sensing of Carbon Dioxide

Carbon dioxide in gaseous samples can be measured in the 3.5 × 10-4 to 0.1 MPa partial pressure range with the use of a fiber-optic luminescent sensor operated in the time-correlated single photon counting (TC-SPC) detection mode. The sensitive tip is fabricated with tris[2-(2-pyrazinyl)thiazole]ruthenium(II) electrostatically immobilized onto carboxymethyl-Sephadex gel. The photoexcited dye is dynamically quenched by hydrogenphthalate generated upon permeation through silicone and dissolution of CO2 into the indicator gel phase containing phthalate buffer of pH 7.3. The nonlinear response of the optical indicator is shown to obey the calculated complex relationship between its emission lifetime and the PCO2. Luminescence decays (293 > τ > 173 ns) of the polymer-supported indicator are strictly exponential in the 0–100% CO2 range. Relative standard deviation values ( n = 7) of 1.9, 1.2, and 1.7% have been measured for 0.0044, 0.023, and 0.092 MPa CO2 in argon, respectively; almost twice as much were obtained when the sensor was operated in the emission intensity mode. The temperature effect (6.1 ns K-1) on the sensitive membrane and (linear) cross-sensitivity to oxygen are discussed as well. The working principle put forward allows one to monitor CO2 using the same optoelectronic instrumentation already well developed for phase-sensitive luminescence optosensing of O2 with pH-independent Ru(II) indicators.

Analysis of organic acids in industrial samples comparison of capillary electrophoresis and ion chromatography

The determination of small organic acids in a variety of industrial samples by capillary electrophoresis was accomplished using a phthalate buffer and indirect UV detection. Various parameters affecting the analysis, including the composition and pH of the electrolyte, were optimized so that fast, sensitive and robust separation were possible. The sensitivity, limit of detection and reproducibility of the method were evaluated under optimized conditions. The method was found to be applicable to a wide variety of samples, ranging from simple aqueous solutions to complex plant organic streams. Comparison of this method to an ion chromatographic method used previously indicates that the CE technique offers a number of attractive features which significantly improve the efficiency and productivity of the organic acid analysis.

Equations for the Calculation of the pH of Buffer Solutions Containing Potassium Hydrogen Phthalate, Dipotassium Phthalate, and Potassium Chloride at 298.15 K

Published experimental thermodynamic data at 298.15 K for aqueous mixtures of H2Ph, KHPh, and KCl, of KHPh, K2Ph, and KCl, and of KHPh and KCl, where H2Ph means phthalic acid, KHPh potassium hydrogen phthalate, and K2Ph dipotassium phthalate, were used to test the methods for calculation of the pH values of phthalate buffer solutions. Equations for ionic activity coefficients are used in these methods. It is shown that all data used, up to an ionic strength of about 0.5 mol kg-1, can be predicted almost within experimental error by two methods. In one of these methods, equations of the modified Guggenheim type are used for ionic activity coefficients, and in the other equations of the Pitzer type are used. Several sets of phthalate buffer solutions are suggested in the pH range 3.8−5.3, e.g., for calibration solutions for glass electrode cells or for constant-pH reaction media where the pH is known. In the recommended sets, the pH values of the buffer solutions have been calculated by the Guggenheim method, and the pH predictions of the Pitzer method agree with those in most cases within 0.01 at least up to ionic strengths of about 0.15 mol kg-1. The recommended pH = 4.005 of the standard reference solution (0.05 mol kg-1 KHPh solution) agrees closely with the value suggested in the present study (4.003) for this solution.

Nitrosation kinetics of phenolic components of foods and beverages

The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5–5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO+/NO2H2+ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol > phenol ≫ p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH# against ΔS# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO+/NO2H2+. © 1997 John Wiley & Sons, Inc.

Systematic investigation on the corrosion of iron under conditions relevant to Storage of nuclear waste

AbstractCorrosion tests were performed on steel samples in q‐brine (pH 4.9), and for comparison in phthalate buffer (pH 4.9) and borate buffer (pH 8.4) at 170°C for 30 h in an autoclave. The samples were subsequently investigated by a wide variety of electrochemical, optical and UHV methods. A systematical combination of both non‐modifying and modifying methods was employed to allow for all measurements to be performed on a small number of samples.In borate buffer (pH 8.4), a thick (200 nm), homogeneous passivating oxide layer is found to build up on iron under test conditions (170°C, 30 h), resembling the anodic oxide layer (+ 1 V, 25°C) with respect to its optical and n‐semiconducting properties. No evidence for a barrier‐type layer is found for samples treated in phthalate buffer (pH 4.9) at 170°C for 30 h. The iron surface is covered by a precipitate layer in this case. In the chloridic q‐brine, a precipitate layer of Mg‐Fe‐oxichlorides is formed and large‐scale active corrosion is observed.

Amperometric flow-injection method for the assay of l-ascorbic acid based on the photochemical reduction of Methylene Blue

Ascorbic acid (AA) is determined by amperometric detection based on the photochemical reduction of Methylene Blue (MB +) in 0.1 M phthalate buffer at pH 3.8. In this medium, MB + using flow-injection analysis. The carrier stream is 1 mM MB + is reduced quasi-reversibly at a glassy carbon electrode at −0.34 V vs. Ag/AgCl, while AA is oxidized irreversibly at about 0.3 V. The reactor is irradiated with a 500 W halogen lamp to facilitate the development of the photochemical reaction. A laboratory-built wall-jet electrode system was used. The Leucomethylene Blue formed in the reaction is detected at +0.050 V. At 2.2 ml min −1 and using a sample loop of 43 μl, the method allows the determination of AA in the range 5.0–90.0 μg ml −1, with a relative standard deviation of 1.3–4.8%, a detection limit of 1.9 μg ml −1 and a sampling frequency of 45–50 h −1.

Surface analytical examination of passive layers on Cu-Ni alloys part II. Acidic solutions

The formation and chemical structure of passive layers on Cu-50Ni and Cu-20Ni in acidic electrolytes have been examined with X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). Phthalate buffer pH5.0 and 0.005 M H 2SO 4 + 0.995M K 2SO 4 pH2.9 have been used for passivation. The corrosion behaviour of the alloys is characterized by the characteristic properties of both alloy components, i.e. increased dissolution of Cu and passivating properties of Ni in acidic electrolytes. A similar multilayer structure with an outer hydroxide and an inner oxide with lower valent cations in an inner position is found as for alkaline solutions. The incorporation of Cu-ions in the outer hydroxide part is extremely small and approaches zero for low pH as a consequence of the increased dissolution rate of Cu 2+ for acidic electrolytes.

Electrochemical Oxidation of ZrN Hard (PVD) Coatings Studied by XPS

Zirconium nitride (ZrN) belongs to the group of technologically important materials, namely hard tribological coatings. X-ray photoelectron spectroscopy (XPS) in combination with polarization experiments and electrochemical a.c. impedance spectroscopy has been used to study the composition, structure, thickness and electronic properties of layers formed by electrochemical oxidation of ZrN in phthalate buffer (pH 5.0). Results are compared to those obtained for layers formed by thermal oxidation at elevated temperature, i.e. ZrO2 , as well as by air oxidation at room temperature. Electrochemical oxidation of ZrN to ZrO2 proceeds via the formation of a mixed oxynitride/oxide layer, which then transforms into oxide at sufficiently positive potentials. Angle-resolved XPS measurements contribute to a better understanding of the in-depth layer structure. Exposure of ZrN to air at room temperature results in the formation of a thin oxynitride/oxide layer. The layer exhibits a gradually changing in-depth distribution of various species, i.e. nitride, oxynitride and oxide. Analysis of XPS valence band spectra offers valuable information concerning the electronic properties of investigated materials. The experimental valence band spectrum for ZrN correlates well with a theoretically calculated density-of-states diagram from the literature. In contrast to ZrN, which is a metallic conductor, layers formed by electrochemical oxidation, as well as by air oxidation, exhibit insulating properties. The insulating character of the formed layers is supported also by a decreased current density in subsequent cycles in cyclic voltammograms, as well as by the resistivity value (∽1012 Ω · cm) calculated from a.c. impedance measurements. Therefore, the oxide layer formed on ZrN is stable and prevents further oxidation of the ZrN substrate.

Sensitive and selective method for the determination of sodium monofluoroacetate by capillary zone electrophoresis

Sodium monofluoroacetate (SMFA) is a highly toxic substance and its determination is needed in several areas. Its chromatographic (GC or HPLC) determination is difficult because of its ionic and hydrophilic properties. A simple, sensitive and selective capillary zone electrophoretic method is described for the determination of SMFA. It is well separated from structurally related compounds (formate, acetate, chloroacetate, bromoacetate, etc.) in an acidic electrolyte buffer containing 5 mmol/l phthalate (pH 4.61) and 0.3 mmol/l cetyltrimethylammonium bromide or in a basic electrolyte solution containing 5 mmol/l 4-hydroxybenzoate, 0.3 mmol/l and 10 mmol/l ammonium (pH 9.49). Good resolution was achieved at relatively low electric field (200–250 kV/cm) and concentration (0.3 mmol/l). The separation selectivity was improved in acidic phthalate buffer. Using bromoacetate as internal standard, the calibration graph for SMFA was linear over the concentration range 1–10 μg/ml. The detection limit was 0.4 μg/ml. The method was applied to the determination of SMFA in rodenticide baits.

Mechanism of oxidation of aromatic amines by peroxomonosulphate – a kinetic study

AbstractOxidation of aromatic amines (substrate) by peroxomonosulphate (PMS) in phthalate buffers at various temperatures revealed first‐order dependence on [PMS] as well as [Substrate]. Rate of oxidation was found to increase with an increase in pH as well as dielectric constant (D) of the medium. The most plausible mechanism involving PMS− and substrate in rate limiting step was proposed. Hammett's plot of log‐rate constant versus σ deviated from linearity. Deviations were explained due to para resonance interaction energies. © 1995 John Wiley & Sons, Inc.

Surface Analytical Investigations of Electrochemically Formed Passive Layers on Binary Fe/Al Alloys

Passive layers have been formed on Fe/Al alloys under well‐controlled electrochemical conditions. These layers were studied by x‐ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) without any exposure to the laboratory atmosphere during the specimen transfer from the electrolyte to the ultrahigh vacuum. The presence of aluminum reduces the active dissolution of the alloys in weakly acidic electrolytes such as phthalate buffer. This leads to lower anodic current densities compared to pure iron. The passive layer thickness due to the preparation conditions varies from 3 to 6 nm. Both components (Al and Fe) enter the passive layer, but Al is significantly enriched. XPS and especially ISS depth profiles show an Al concentration maximum at a depth of 2 nm which is roughly in the center of the passive layer. Apparently the passive film is a mixed oxide with a pronounced concentration gradient of both cationic species. Galvanostatic reduction and dissolution of the passive layers in combination with XPS permits the determination of an electrochemical depth profile which confirms the results of the sputter depth profiles. A clearly separated sublayer structure of different oxidation states [Fe(II) and Fe(III)] was only found in the passive layers on pure iron. Its existence in the passive layers on Fe/Al alloys could not be confirmed. The preparation parameters, especially the passivation time, cause changes in the concentration gradients. Closer examinations of these effects by time‐resolved measurements provide kinetic information on the growth and chemical changes of the passive layer. A model describing the observed effects during the layer formation is presented.

Electrochemical and thermal oxidation of TiN coatings studied by XPS

AbstractX‐ray photoelectron spectroscopy (XPS) has been used to investigate the electrochemical and thermal oxidation of titanium nitride (TiN) coatings prepared by physical vapour deposition (PVD) at 200°C. Electrochemical oxidation of TiN was carried out at various potentials in phthalate buffer solution (pH 5.0). Evaluation of the XPS Ti 2p and N 1s spectra showed the presence of nitride, oxynitride and oxide species in the layer formed by anodic oxidation. The electrochemical oxidation of TiN to TiO2 proceeds through the formation of a mixed oxynitride/oxide layer, which transforms into oxide (TiO2) at sufficiently positive potentials (E > 1.1 V vs. SHE). The oxidation of TiN to TiO2 is accompanied by the formation of molecular nitrogen (N2). The thickness of the oxide layer reaches ∼7 nm after oxidation at the highest potential (1.9 V). A complete coverage of the TiN surface by TiO2 leads to an anodic peak in the polarization curve. On the basis of angle‐resolved XPS measurements, two types of oxynitride species are identified, which are distributed differently throughout the oxidized layer.X‐ray photoelectron spectroscopy depth profiles of TiN oxidized at 450°C and 600°C in an oxygen flow reveal that at the lower temperature an oxynitride layer is formed, whereas a thick TiO2 layer appears on top of TiN at the higher temperature. The interface between the nitride and oxide phases is relatively sharp. It is suggested that the mechanism of TiN oxidation proceeds by a progressive replacement of nitrogen by oxygen. The TiN coatings can be used up to 600°C as a protective coating in an oxygen atmosphere.Valance band spectra of TiN, as well as of electrochemically and thermally oxidized TiN, are presented and discussed.

KCl potentiated inactivation of poliovirus 1 by free chlorine at pH 4.5.

At 5 degrees C in phthalate buffer at pH 4.5, poliovirus 1 was destroyed 60 to 70% more rapidly by free chlorine (FC) in the presence of 1,262 mg/L (approximately 0.0169 M) KCl than in the absence of KCl. At 5 degrees C, more than 99.9% of FC exists as HOCl at pH 4.5. Since buffers themselves may have a marked potentiating effect on the virus-inactivating capability of FC, and because a maximum ion potentiating effect may occur, the actual degree of potentiation of HOCl by KCl may be much greater. Because the level of chlorination for drinking water is in large part determined by the rate at which the chlorines inactivate viruses in laboratory studies, the potentiation of FC by ions normally present in drinking waters may permit reducing chlorination levels and with them the levels of carcinogenic and otherwise toxic organic halides produced by chlorination.

High performance liquid chromatographic determination of aluminium in natural waters in the form of its lumogallion chelate

A high performance liquid chromatographic method for the determination of ultra trace amount of aluminium in natural waters has been developed using lumogallion as a precolumn reagent for fluorimetric detection. The highly fluorescent Al-lumogallion chelate ( λ ex 500 nm, λ em 574 nm) was separated on a LiChrosorb RP 18 column with an eluent containing 3:7 acetonitrile/0.02 M potassium hydrogen phthalate buffer (pH 4.7) containing 10 −5 M lumogallion. The proposed system provides a simple, quick, selective and sensitive method for the determination of ultra-trace amount of aluminium in water samples. The detection limit defined as three times the standard deviation of the blank signal, was 0.05 μg/l. in water samples for 100 μl injection. The tolerance limits were 5 mg/l. for Fe(III) and F − and over 10 mg/l. for other foreign ions. The sensitivity of the method was independent of salinity. This method had been used for the direct determination of aluminium in both tap and coastal sea-waters without any preconcentration steps.

Electrochemical, ellipsometrical and surface analytical investigations of passive layers on binary Fe/Al alloys

AbstractX‐ray photoelectron spectroscopy, ISS, ellipsometry, electrochemical impedance spectroscopy and electrochemical methods have been used to investigate the passive layers (PAL) on iron/aluminium alloys with low contents of Al (2 up to 12 wt.%). Ellipsometric measurements were performed during the galvanostatic reduction of PAL formed on Fe/8Al in 0.5 M Na2SO4/H2SO4 (pH 3.85) at various potentials. Combining the results of ellipsometric singlelayer model evaluations and of the electrochemical reduction curves it was found that the outer part of the PAL mainly consists of the relatively stable γ‐Fe2O3. Its fraction to the overall thickness of the PAL gives a maximum value when the alloy is passivated at +1 VSHE. At higher potentials, porous films with both decreasing capacities and polarization resistances, measured by impedance spectroscopy, are formed. The XPS and ISS sputter depth profiles of PAL on Fe4/12Al formed in phthalate buffer (pH 5) at +1 VSHE showed an Al enrichment in the centre of the layers. The reductive dissolution of the passive layer in close combination with XPS analysis at distinct states of this process yields similar depth profiles. These results suggest the formation of mixed Fe/Al oxides or oxide compounds.

Separation of condensed phosphates using capillary zone electrophoresis with indirect UV detection

A capillary zone electrophoresis (CZE) separation of ortho-, pyro- and tripolyphosphate anions using a phthalate buffer and indirect UV detection is described. Advantages of a CZE method for phosphates include speed, efficiency and unique selectivity. Quantitative parameters and application to the analysis of a commercial sample are presented.