Liquid sieve chromatography

LSC liquid sieve chromatography MAD mean absolute deviation... 

This separation method is based on the molecular size of analytes. Analytes pass through porous stationary phase materials having different pore sizes, and molecular interactions between analytes and the stationary phase surface must be eliminated. A very strong solvent is therefore required in this system. This system is also called gel filtration liquid chromatography, gel-permeation liquid chromatography, or molecular sieve chromatography. This system is used to... 

Cassidy and Niro [13] have applied high-speed liquid chromatography combined with infrared spectroscopy to the analysis of polyoxyethylene surfactants and their decomposition products in industrial process waters. Molecular sieve chromatography... 

Considerable progress has been made in the separation of 1,3-PD, including evaporation, distillation, membrane filtration, pervaporation, molecular sieves, chromatography, liquid-liquid extraction, reactive extraction, and salting-out extraction (SOE). However, all these methods have some limitations. 

Cassidy and Niro [13] have applied high-speed liquid chromatography combined with infrared spectroscopy to the analysis of polyoxyeihylene surfactants and their decomposition products in industrial process waters. Molecular sieve chromatography combined with infrared spectrometry give a selective method for the analysis of trace concentrations of these surfactants. These workers foimd that liquid-solid chromatography and reversed phase chromatography are useful for the characterisation and analysis of free fatty acids. 

A reliable chromatographic method has been developed for the quantitative aneilysis of hydrophobic impurities in water-soluble polymeric dyes. The method utilizes both the molecular sieve effect of normal gel permeation chromatography and solute-column packing interaction, modified by solvent composition. This method eliminates the need to extract the impurities from the polymeric dye with 100 extraction efficiency, as would be required for an ordinary liquid chromatographic analysis. 

To a solution of the titanocene(II) reagent 29 in THF (42 mL) in a 300-mL round-bottomed flask, prepared from titanocene dichloride (6.54 g, 26.3 mmol), magnesium turnings (0.766 g, 31.5 mmol), triethyl phosphite (8.96 mL, 52.5 mmol), and finely powdered 4 A molecular sieves (1.31 g) according to the procedure described above, was added a solution of l,l-bis(phenylthio)cyclobutane (63 2.29 g, 8.40 mmol) in THF (14 mL). The reaction mixture was stirred for 15 min. and then a solution of (S)-isopropyl 3-phenylpro-panethioate (91 1.46 g, 7.00 mmol) in THF (21 mL) was injected dropwise over a period of 10 min. The reaction mixture was refluxed for 1 h, then cooled, whereupon 1 m aq. NaOH solution (150 mL) was added. The insoluble materials produced were removed by filtration through Celite and washed with diethyl ether. The aqueous layer was separated and extracted with diethyl ether. The combined ethereal extracts were dried (Na2S04), filtered, and concentrated. The residual liquid was purified by column chromatography (silica gel, hexane) to afford 1.33 g (77%) of (l-isopropylthio-3-phenylpropan-1 -ylidene) cyclobutane (92). 

When adsorbents are used to dry gases or liquids, often in a flow system, the adsorbents may need pre- or post-treatment to avoid hazards. Thus, when ethylene was contacted with molecular sieve not previously treated with dilute ethylene, the adsorption exotherm heated the bed to red heat and ruptured the drier. When peroxide-containing ethers are simultaneously dried and purified by chromatography (passage through an alumina column), the peroxides are concentrated on the alumina, which must be treated before disposal. 

In gas-solid chromatography (GSC) the stationary phase is a solid adsorbent, such as silica or alumina. The associated virtues associated therewith, namely, cheapness and longevity, are insufficiently appreciated. The disadvantages, surface heterogeneity and irreproducibility, may be overcome by surface modification or coating with small amounts of liquid to reduce heterogeneity and improve reproducibility 4,15). Porous polymers, for example polystyrene and divinyl benzene, are also available. Molecular sieves, discussed in Chapter 17, are used mainly to separate permanent gases. 

The usual procedures of fractional, azeotropic, or extractive distillation under inert gases, crystallization, sublimation, and column chromatography, must be carried out very carefully. For liquid, water-insoluble monomers (e.g., styrene, Example 3-1), it is recommended that phenols or amines which may be present as stabilizers, should first be removed by shaking with dilute alkali or acid, respectively the relatively high volatility of many of these kinds of stabilizers often makes it difficult to achieve their complete removal by distillation. Gaseous monomers (e.g., lower olefins, butadiene, ethylene oxide) can be purified and stored over molecular sieves in order to remove, for example, water or CO2. 

A continuous-flow reactor with a fixed catalyst bed was employed at pressurized conditions. Gaseous dimethyl ether was supplied to the reactor at its vapor pressure with carbon monoxide while liquid reactants such as methyl acetate, methyl iodide, and water were fed with microfeeders. Methyl acetate used in this experiment was dehydrated by Molecular Sieve 5A before use. A part of the reaction mixture was sampled with a heated syringe and was analyzed by gas chromatography. 

---