Search results for "SOLVENT"
showing 10 items of 1395 documents
Role of solvent and base in the silanization reaction of silicas for reversed-phase high-performance liquid chromatography
1984
Reversed-phase packings were synthesized by reaction of n-alkyldimethylchloro- and trifluoroacetoxysilanes with silicas of 15 and 25 nm pore size, employing tetrahydrofuran, N,N-dimethylformamide, benzene, diethyl ether, dichloromethane and acetonitrile as solvents and triethylamine, pyridine, triazole, quinuclidine, 2,4- and 2,6-lutidine and imidazole as bases. With dichloromethane as solvent and 2,6- lutidine as base, n-alkyldimethyltrifluoroacetoxysilanes did not yield n-alkyl ligand densities higher than those obtained with n-alkyldimethylchlorosilanes under identical conditions. With a given base and given n-alkyldimethylchlorosilane the solvent type was found to exert a noticeable inf…
Large scale fractionation of pullulan and dextran
2006
Abstract A recently developed large scale fractionation technique named continuous spin fractionation (CSF) was applied to fractionate pullulan and dextran. 450 g of pullulan with a broad molecular weight distribution were fractionated using water as solvent and acetone as precipitant. In this study, we have in five CSF runs prepared three fractions with apparent M ¯ w * values ranging from 17.6 to 413 kg mol−1. Seventy grams of dextran were fractionated with a mixed solvent of water plus methanol. Five fractionation steps resulted in four samples with M ¯ w values between 4.36 and 18.2 kg mol−1.
Effect of solvents on the selectivity of terbutylazine imprinted polymer sorbents used in solid-phase extraction
2002
A solid-phase extraction sample preparation method using a molecularly imprinted polymer (MIP) selective for the triazine type pesticide terbutylazine has been developed. The method involves preconcentration from large volumes of water samples on a C18 disk coupled to selective clean-up on the MIP. The method has been optimised by studying the recovery and retention of terbutylazine and some other structurally related triazine derivates as a function of the selective washing solvent used. The effect of the water content of the selective washing solvent was also investigated on the recovery of the MIP. River water samples were analysed with the coupled technique, and efficient clean-up of th…
Preferential solvation of a dicyanate ester monomer and poly(sulfone) in different organic solvents by size-exclusion chromatography.
2002
Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in …
Pressurized liquid extraction of organic contaminants in environmental and food samples
2015
Pressurized liquid extraction (PLE) is an automated technique that uses elevated temperature and pressure to achieve exhaustive extraction from solid matrices, so reducing solvent consumption and enhancing sample throughput when compared with traditional procedures. Hence, it can be considered an environment-friendly technique, generating small volumes of waste and reducing costs and time. This review focuses on application of this green technique to the analysis of organic contaminants in food and environmental matrices for monitoring purposes. We examine fundamentals and key aspects of the development of a PLE method, including pressurized hot-water extraction, together with some relevant…
Resolution assessment and performance of several organic modifiers in hybrid micellar liquid chromatography
2001
The performance of four criteria that measure the elementary resolution (modified selectivity, modified RS, peak purity, and orthogonal valley-to-peak ratio) was critically assessed using as global resolution function, the product of elementary measurements. The peak purities and valley-to-peak criteria yielded the best description of the overall separation according to the shape of the resolution surfaces compared to the peak arrangements in the chromatograms, the capability of defining unambiguously the composition regions of complete resolution, and the resolution achieved in the predicted optimums. Peak purities were used to compare the effect of five organic modifiers (1-propanol, 1-bu…
Separation of U(VI) and Th(IV) from Some Rare Earths by Thin Layer Chromatography with Di‐(2‐Ethylhexyl)‐Dithiophosphoric Acid on Silica Gel
2005
Abstract Separation of U(VI) and Th(IV) from some rare earths by TLC has been studied using silica gel H and silica gel H impregnated with ammonium nitrate as the stationary phase. The solvent mixture ethyl‐methyl‐ketone–tetrahydrofuran (6∶3, v/v) containing di-(2‐ethylhexyl)-dithiophosphoric acid was used as the mobile phase. When silica gel H impregnated with 2.5 M NH4NO3 was used as stationary phase, the resolution was much improved and the separation of rare earths from each other was also achieved. The tetrad‐effect was observed in variation of R*m versus the atomic number of rare earths.
Determination of pesticides and their degradation products in soil: critical review and comparison of methods
2004
18 páginas, 5 figuras, 5 tablas.
Spectrophotometric Determination of Hydralazine with 2-Hydroxy-1-naphthaldehyde in Pharmaceuticals
1991
Abstract A new extraction-spectrophotometric method for the determination of hydralazine, based on its reaction with 2-hydroxy-1-naphthaldehyde at 25 °C, is described. The calibration curve was linear between 0.4 and 6 mg/mL of hydralazine. The molar absorbtivity of the product at 408 nm is 40 900 L · mol − 1 · cm − 1 . The method described was applied to the analysis of hydralazine in pharmaceutical preparations containing reserpine, hydrochlorothiazide, bendrofluorthiazine, propranolol, and other substances. The agreement with the U.S.P. XXI method was satisfactory for tablets and injections, but not for pellets.
Supercritical CO2 extraction of essential oils from orange peel
1996
The supercritical fluid extraction of orange essential oil was studied using dehydrated orange peel (0.0538 kg H2O kg−1 dm) from naveline cultivars as raw material and CO2 as solvent. The effect of operation conditions was analyzed in a series of experiments at 313 and 323 K and pressures between 1 and 25 MPa. Furthermore, the effect of CO2 flow rate and particle size of orange peel was studied in the range of 0.5 to 3.5 kg h−1 and 0.1 to 10 mm. The subcritical CO2 dissolves hardly any essential oils, however, on reaching the critical point, the amount of essential oils dissolved increased with pressure, within the range of pressures considered in this study. Increasing solvent mass flow de…