Search results for "maleic acid"
showing 10 items of 17 documents
Determination of ethyl sulfate – a marker for recent ethanol consumption – in human urine by CE with indirect UV detection
2006
A CE method for the determination of the ethanol consumption marker ethyl sulfate (EtS) in human urine was developed. Analysis was performed in negative polarity mode with a background electrolyte composed of 15 mM maleic acid, 1 mM phthalic acid, and 0.05 mM cetyltrimethylammonium bromide (CTAB) at pH 2.5 and indirect UV detection at 220 nm (300 nm reference wavelength). This buffer system provided selective separation conditions for EtS and vinylsulfonic acid, employed as internal standard, from urine matrix components. Sample pretreatment of urine was minimized to a 1:5 dilution with water. The optimized CE method was validated in the range of 5-700 mg/L using seven lots of urine. Intra-…
Investigation of the Interpolymer Complex between Hydroxypropyl Cellulose and Maleic Acid-Styrene Copolymer, 1
2004
The hydrogen bonding-interpolymer association of hydroxypropyl cellulose (HPC) with maleic acid-styrene (MAc-S) copolymer has been investigated in dilute aqueous solution by viscometry, turbidimetry and potentiometry. At a mixing ration between MAc-S and HPC of 10:90, the solution exhibits a phase separation upon heating, while for other mixing ration no phase separation could be detected. The stability of the interpolymer complex (IPC) increases as the temperatures rises. The stoichiometry of the IPC, in mole units, was estimated as being MAc-S:HPC=5:2. The thermodynamic functions (enthalpy and entropy) of the complexation process have been determined.
Oxide anodes in electro-organic oxidation. Oxidation of maleic addon tungsten oxide anodes
1982
The electrochemical oxidation of maleic acid on tungsten anodes has been investigated. Glyoxal and carbon dioxide were the main products together with tartaric acid and acetaldehyde. Glyoxal is also obtained as the main product from the oxidation ofd-tartaric acid. Under the same conditions succinic acid is completely oxidized to carbon dioxide and water. The anodic dissolution of tungsten and the oxidation of water to oxygen become predominant in the final stages of the electrolyses.
The Preparation and Characterization of New Antazoline Salts with Dicarboxylic Acids
2015
New antazoline salts with organic acids (fumaric acid, oxalic acid, and maleic acid) were prepared. The effect of the crystallization solvent and mechanochemical treatment on the crystalline forms of these salts was studied. Two polymorphs of antazoline hydrogen maleate were identified and their relative stability was determined. The molecular structures of antazoline hydrogen oxalate and antazoline hydrogen maleate showed differences in antazoline cation conformation. In crystal structures of all salts both imidazoline nitrogens of antazoline cation are involved in hydrogen bond formation with carboxyl groups of the acid.
Heterogeneous photocatalytic aqueous succinic acid formation from maleic acid reduction
2022
This study reports the anaerobic reduction of maleic acid to succinic acid in aqueous dispersion of different TiO2 based photocatalysts. Some home prepared and commercial solids containing different polymorphic phases of TiO2 and loaded with Pt and Ru were compared at different acidic pHs. The aim of the work was to verify the feasibility of the process and to determine the best samples and the optimal experimental conditions of the reaction. The best selectivity towards succinic acid was 23.2 % at 70 % of maleic acid conversion. Fumaric acid was also formed as another high added value compound, and its quantity was related to the experimental conditions and the photocatalyst used.
Oxidation of carboxylic acids in water at IrO2-Ta2O5 and Boron Doped Diamond anodes
2011
Abstract A detailed study was dedicated to the anodic oxidation of three carboxylic acids (namely, oxalic, formic and maleic acid) with the objective to evaluate in a systematic way the effect on the oxidation of carboxylic acids of numerous relevant parameters, including the nature and the concentration of the carboxylic acid, the alimentation regime (potentiostatic vs. amperostatic), the current density and the working potential values, the flowdynamic regime, the temperature and the nature of the electrode material. It was observed that the effect of some operative parameters strongly depends on the nature of the electrode and of the carboxylic acid. As an example, the efficacy of abatem…
Dentin wettability enhancement for three irrigating solutions and their effect on push out bond strength of gutta percha / AH Plus
2014
Background: The aim of this study was to investigate the effect of wettability enhancement for 17% EDTA, 2.5% sodium hypochlorite and 7% maleic acid solutions on push out bond strength of gutta percha /AH Plus to root dentin. Materials and Methods: One hundred and eight extracted single rooted human lower premolars were instrumented up to Protaper Universal F5 then irrigated with 3ml of 2.5% NaOCl after each file. Irrigants were prepared and a pilot study for determination of Tween 80 concentration yielding the lowest surface tension value in every solution was conducted. Samples were randomly divided into a control group and two experimental groups (17% EDTA and 7% Maleate), further split …
Interpolymer complex between hydroxypropyl cellulose and maleic acid-styrene copolymer: phase behavior of semi-dilute solutions.
2005
Summary: The phase behavior of a water/hydroxypropyl cellulose/maleic acid–styrene copolymer (H2O/HPC/MAc-S) system was investigated in the semi-dilute range by turbidimetry, rheology, and optical microscopy. The two polymers under investigation form interpolymer complexes via hydrogen bonding. In the case of a total polymer concentration of cpol = 5 mg · mL−1 a second phase segregates upon heating the homogeneous ternary system. By applying a constant shear rate ( = 50 s−1) the phase separation temperature of the system is 10–15 °C lower than for an unsheared one. For cpol = 10 mg · mL−1 phase separation has already occurred at room temperature when the two binary polymer solutions are mix…
Impact of hydrothermal ageing on the thermal stability, morphology and viscoelastic performance of PLA/sisal biocomposites
2016
The influence of the combined exposure to water and temperature on the behaviour of polylactide/sisal biocomposites coupled with maleic acid anhydride was assessed through accelerated hydrothermal ageing. The biocomposites were immersed in water at temperatures from 65 to 85 °C, between the glass transition and cold crystallisation of the PLA matrix. The results showed that the most influent factor for water absorption was the percentage of fibres, followed by the presence of coupling agent, whereas the effect of the temperature was not significant. Deep assessment was devoted to biocomposites subjected to hydrothermal ageing at 85 °C, since it represents the extreme degrading condition. Th…
Determination of fatty alcohol ethoxylates with diphenic anhydride derivatization and liquid chromatography with spectrophotometric detection
2009
A method for the determination of fatty alcohol ethoxylates (FAEs) using diphenic anhydride as derivatization reagent and RP-HPLC separation with UV-vis detection is presented and compared to derivatization with maleic, phthalic, and other cyclic anhydrides. With these anhydrides, the reaction rates increased when urea was added to the reaction medium, and the yields did not decrease when the samples contained moderate amounts of water. Gradient elution on a C8 column was performed with water/acetonitrile in the presence of 0.1% acetic acid. The use of diphenic anhydride was advantageous for both the chromatographic separation and the detection. Specifically, sensitivity at 200 and 220 nm w…