Search results for "Critical"

A New Simple Static Method for the Determination of Solubilities of Condensed Compounds in Supercritical Fluids

2002

Abstract A simple static method based on gravimetric measurements has been adopted to measure the solubility of benzenecarboxylic acid, 2-hydroxy-benzenecarboxylic acid, 4-hydroxy-benzenecarboxylic acid and 1,8-dihydroxyanthraquinone along several isotherms in the temperature range 318–357 K and the pressure interval 7–23 MPa. Solubility data have been correlated with the Zieger–Eckert approach, using the Fedor atomic and group contribution method to estimate the solubility parameter and the molar volume of the solutes. A good agreement was obtained between data reported in the literature and those determined using the proposed method which allows one to measure solubility mole fraction as …

Determination of alinidine in human plasma by high-performance liquid chromatography.

1981

Retention mechanisms in micellar liquid chromatography.

2008

Micellar liquid chromatography (MLC) is a reversed-phase liquid chromatographic (RPLC) mode with mobile phases containing a surfactant (ionic or non-ionic) above its critical micellar concentration (CMC). In these conditions, the stationary phase is modified with an approximately constant amount of surfactant monomers, and the solubilising capability of the mobile phase is altered by the presence of micelles, giving rise to diverse interactions (hydrophobic, ionic and steric) with major implications in retention and selectivity. From its beginnings in 1980, the technique has evolved up to becoming a real alternative in some instances (and a complement in others) to classical RPLC with hydro…

Perspective: The Asakura Oosawa model: A colloid prototype for bulk and interfacial phase behavior

2014

In many colloidal suspensions, the micrometer-sized particles behave like hard spheres, but when non-adsorbing polymers are added to the solution a depletion attraction (of entropic origin) is created. Since 60 years the Asakura-Oosawa model, which simply describes the polymers as ideal soft spheres, is an archetypical description for the statistical thermodynamics of such systems, accounting for many features of real colloid-polymer mixtures very well. While the fugacity of the polymers (which controls their concentration in the solution) plays a role like inverse temperature, the size ratio of polymer versus colloid radii acts as a control parameter to modify the phase diagram: when this …

Supercritical fluid extraction of pesticides

1989

The extraction behaviour of 10 μg samples of five pesticides and some related compounds from glass wool with supercritical CO2 has been investigated under several conditions (10 MPa, 20 MPa extraction pressure, 313 K, dry and water saturated CO2). The extraction fluid was decompressed over a line of little columns, filled with 3μ Si60 or RP18, and the amount of deposited material was analyzed by HPLC for each of these columns. Due to the progressive pressure/density reduction along the line, the solubility diminishes and hence the compounds are deposited according to their polarity/vapor pressure earlier or later on the line. Thus extraction and prefractionation of compounds of different po…

Sunscreen analysis

2005

Although there are no official analytical methods for UV filters determination in sunscreen cosmetics, their maximum content are regulated by legislation, and then analytical methods to control these products are necessary. In this paper, analytical methods for UV filters determination in cosmetics, which can be found in the literature, are reviewed. The usefulness of the analytical methods, techniques and sample preparation is discussed. The analytical methods used for the determination of UV filters in other type of samples are commented upon. Moreover, a brief overview of the European Union legislation concerning UV filters is included.

Role of Phase Behavior and Atomization in the Supercritical Antisolvent Precipitation

2003

An experimental study on supercritical antisolvent (SAS) precipitation has been performed to gain insight into the role of phase behavior and atomization in controlling morphology and dimension of precipitates. The mixture yttrium acetate/dimethyl sulfoxide has been used as the main model system and supercritical CO 2 has been used as the antisolvent. Two SAS apparatuses (laboratory and pilot scale) with two injector arrangements and operating with various injector diameters in the range 60-500 μm have been used. The results showed that operating above the mixture critical point (MCP) of the ternary mixture yttrium acetate/dimethyl sulfoxide/ carbon dioxide, sub-micrometric particles are ge…

High-pressure solubility data of system ethanol (1)+catechin (2)+CO2 (3)

2001

Abstract Supercritical fluid extraction posses several advantages over traditional liquid–solvent-based extraction methods including improved selectivity, expeditiousness, automation and environmental safety. Fluid phase equilibrium data is essential for study the viability of supercritical extraction and the design of the extraction columns often used for this type of separations. During the past few years it has been demonstrated that phenolic compounds, such catechins and procyanidins from seeds, contribute to both the flavour properties and the pharmacological effects of wine. The extraction of catechin using supercritical CO2 is not possible, it only extracts traces of product, probabl…

High-pressure solubility data of the system resveratrol (3)+ethanol (2)+CO2 (1)

2001

Abstract Supercritical fluid extraction possesses several advantages over traditional liquid-solvent-based extraction methods, including improved selectivity, expeditiousness, automation and environmental safety. Fluid-phase equilibrium data are essential for studying the viability of supercritical extraction and the design of the extraction columns often used for this type of separation. Resveratrol has been correlated with serum lipid reduction and inhibition of platelet aggregation, and its cancer chemopreventive activity has recently been reported. The extraction of resveratrol using supercritical CO 2 is not possible; it only extracts traces of product, probably due to its polar nature…

Experimental and fluid dynamic study of continuous supercritical water gasification of glucose

2016

Abstract The supercritical water gasification (SCWG) of glucose as a model compound for H 2 production is studied in term of process development at 25 MPa and 650 °C. Gasification has been investigated using a laboratory scale continuous plant comprising a continuous down flow reactor with a volume of 200 cm 3 , a heat recovery section and pre-heat of the biomass to simulate more closely an industrial design. Feed streams (pure water and glucose solution) are introduced at the top of the vessel and products are extracted from the bottom. The reactor is equipped with various inlet points that allow to modify the inlet position of reacting streams in order to study the effect of stream mixing…