Search results for "aqueous solution"
showing 10 items of 1610 documents
Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N-isopropylacrylamide)
2003
The interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (M w = 1 600 kg/mol) poly(N-isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, T cp decreases steadily with rising polymer concentration up to 10 wt.-%. The application of shear supports phase separation and reduces T cp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected wit…
Mark-Houwink Parameters of Biosynthetic Poly(γ-glutamic acid) in Aqueous Solution
2001
A combined viscosity–light scattering–gel permeation chromatography (GPC) study was carried out on bacterially produced poly(γ-glutamic acid) (PGGA). PGGA samples with weight-average molecular weights ranging from 8×104 up to 8×105 g·mol–1 dissolved in phosphate buffer at 0.13 M ionic strength were used. It was found that the Mark–Houwink relation is acceptably obeyed, giving K and a values of 1.84×10–6 dL·g–1 and 1.16, respectively. As expected, GPC analysis showed that PGGA does not follow the universal calibration plot and that deviations can not be avoided by modifying the ionic strength.
Measurement of interactions between polysaccharides and flavour compounds by exclusion size chromatography: Advantages and limits
1998
Interactions between flavour compounds and polysaccharides have been studied by exclusion size chromatography, the Hummel and Dreyer method. Hydrogen bonding was found between 2-acetyl thiazole and dextrines of different degrees of polymerisation. The number of binding sites and the affinity constant increase by increasing the degree of polymerisation. Hydrogen bonding was also responsible for the interactions between xanthane and 1-octen-3-ol or 2-acetyl pyrazine, with 1 mole of 1-octen-3-ol bound per pentasaccharide repeating unit. Unfortunately, the number of flavour compounds, which can be studied with this method, is limited due to their low water solubility and their low UV absorption.
FIA-fluorimetric determination of adrenaline in pharmaceutical formulations by oxidation with molecular oxygen
1998
The fluorimetric determination of adrenaline is carried out in a continuous-flow assembly and by means of the molecular dissolved oxygen. The sample solution merges with an NaOH stream, then the resulting mixture is heated at 73 °C and led to the flow-cell of the fluorimeter. The flow-assembly is very simple and the procedure is quick (107 samples h−1) reproducible (R.S.D. 0.6%), selective and suitable to be applied to determination of adrenaline in formulations. Calibrations graph are linear over the ranges 0.05–15 and 20–40 mgl−1.
Gas assisted mechanical expression (GAME) for the selective recovery of lipophilic and hydrophilic compounds from olive kernel
2017
Abstract This work is devoted to valorize olive kernel; a by-product produced during olive oil extraction process. For this purpose, aqueous liquid solid extraction (LSE), mechanical expression (ME), supercritical CO2 (SC-CO2) and gas assisted mechanical expression (GAME), processes were compared when applied separately or consequently (ME + GAME), in terms of total phenolic compound (TPC) and oil recovery yields. Results showed that although the high extraction yields of TPC using LSE (61.4 ± 1.3%), the extraction process is economically not viable. However, it was demonstrated that applying ME (1 h at 30 MPa) followed by GAME (1 h at 30 MPa ME and 10 MPa SC-CO2 pressures) allowed recoveri…
Screening and authentication of herbal formulations based on microextraction-assisted voltammetry of microparticles
2015
A simple solid state electrochemical methodology for screening and authentication of herbal formulations is described. The proposed method is based on the recording of the voltammetric response, in contact with aqueous buffers, of microparticulate films of antioxidant compounds resulting from micro-extraction of dried herbal samples with ethanol or acetone. The obtained voltammetric responses led us to differentiate between diverse active components upon application of bivariate and multivariate chemometric techniques. Resolution of herbal preparations containing two or more components is possible when well-separated voltammetric signals are recorded. In favorable cases, such characteristic…
Simultaneous Determination of Adrenaline and Noradrenaline by First Derivative Spectrophotometry in a Fia Assembly
1996
Abstract This article deals with the design of an unsegmented-flow injection manifold for the simultaneous determination of adrenaline and noradrenaline two structurally related compounds with overlapping spectra. An FIA manifold is proposed for the simultaneous determination in which the sample solution is directly injected into a carrier-reagent stream of aqueous NaOH. The selected wavelengths (first derivative) were 394 and 342 nm, for noradrenaline and adrenaline, respectively with an integration time of 0.4 s. The calibration graphs are linear over the range 2.0–30 ppm for both drugs. The method is applied to different synthetic mixtures of both drugs.
The use of utraviolet-visible spectrophotometry in the determination of average properties of nonylphenol ethylene oxide condensates
1983
Ultraviolet spectrophotometry is usd in the determination of average molecular weight (M), average degree of polymerization (X), the hydrophilic-lipophilic balance (HLB) and ethylene oxide percentage of nonylphenol ethylene oxide condensates. The method is based on determination of the absorptivity a, expressed in g lt-1 cm−1, from the absorbances measured at 275 nm for a series of dilutions of an aqeuous ethanolic solution (60:40, v/v/) of a given product, followed by numerical interpolation of this value in the expression a = f(HLB), log a = f(log M), and log a = f(log X). These expressions are obtained from reference samples or samples previously analyzed. The proposed method gives relat…
New Chromogenic Probes into Nanoscopic Pockets in Enhanced Sensing Protocols for Amines in Aqueous Environments
2005
A new sensory MCM-41-based material for the colorimetric sensing and discrimination of amines has been developed.
Micellar Liquid Chromatography: Fundamentals
2015
The reversed phase liquid chromatography (RPLC) mode with surfactant above the critical micellar concentration (CMC) has been called micellar liquid chromatography (MLC). In pure micellar systems, the retention behavior is explained by considering three phases or environments: surfactant-modified stationary phase, bulk aqueous solvent, and micellar pseudo-phase. Surfactant adsorption on the porous RPLC packing affects chromatographic retention, owing to the change of diverse surface properties of the stationary phase. In pure micellar systems, the retention behavior is explained by considering three phases or environments: surfactant-modified stationary phase, bulk aqueous solvent, and mice…