Solvent techniques

There ai e noted the most convenient, simple and chip methods, which ensure the high quality of specimens and can be easily combined with different techniques for analytical pre-concentration of impurities. In particulaidy, it is proposed to make specimens in the form of gel, film or glass in the case of XRF analysis of concentrates obtained by low-temperature crystallization of aqueous solutions. One can prepai e film or organogel specimens from organic concentrates obtained by means of extraction of impurities by organic solvent. Techniques for XRF analysis of drinking, natural and wastewater using considered specimens ai e adduced. 

A major treatise devoted to experimental methods of chemistry is Techniques of Chemistry , edited first by Weissberger, and then by Saunders, Wiley, New York. This publication, which began in 1970, so far consists of 21 volumes, most of them in several parts, covering such topics as electrochemical and spectral methods, kinetic methods, photochronusm, and organic solvents. Techniques of Chemistry is a successor to an earlier series, called Techniques of Organic Chemistry , which appeared in 14 volumes, some of them in more than one edition, from 1945 to 1969. 

Substrate Sub-sample (g) Solvent Technique Cleanup (pgmL- ) ... 

Entry Reaction temp. (°C) Reaction time Solvent Technique Yield (%) Ratio 210 211... 

Eluxyl A process for separating /7-xylene from its isomers, using an adsorbent-solvent technique. The process is based on simulated countercurrent adsorption where the selective adsorbent is held stationary in the adsorption column. The feed mixture to be separated is introduced at various levels in the middle of the column, as in the Sorbex process. The /r-xylene product can be more than 99.9 percent pure. Developed by IFP and Chevron Chemical. A large pilot plant was built in Chevron s site at Pascacougla, MS, in 1994 and a commercial plant on the site was announced in 1996, Since then, the process has been widely licensed. 

Alternatively, lipospheres might be prepared by a solvent technique. In this case, the active agent, the solid carrier, and the phospholipid are dissolved in an organic solvent such as acetone, ethyl acetate, ethanol, or dichloromethane. The solvent is then evaporated and the resulting solid mixed with warm buffer solution, and mixing is continued until a homogeneous dispersion of lipospheres is obtained. 

Methods now used to separate (capture) COj from other gases include solvent techniques and membrane separations. Both methods require energy input to recover COj. More efficient, lower-cost separation techniques would improve the feasibility of CO2 capture. 

JARiddick and W.B.Bunger, "Organic Solvents , Techniques of Chemistry, Volume II, Wiley-lnterscience, Division of John Wiley and Sons, Inc. New York, London, Sydney and Toronto. 

Two-Phase Desorption System. The mixed solvent technique has limited use for complex mixtures since it is more difficult to chromatograph, precludes determination of the polar solvent added, and may cause additional interference to other compounds present. A two-phase system has been developed which is capable of measuring both polar and non-polar organic solvents present simultaneously in work environments (19). 

Riddick, J. A., and W. B. Bunger, 1970, Organic Solvents. Techniques of Chemistry, Vol. 2, 3rd ed., Wiley-Interscience, New York. A very good summary of the various techniques reported for the purification of individual solvents along with some physical data and references to the original literature. 

The system Cl-buty 1-natural rubber (or cw-polyisoprene) could not be resolved by differential solvent techniques because the polymeric solubility parameters were too similar. At one end of the spectrum—i.e., with styrene at — 25 °C—natural rubber could be highly swollen while restricting the chlorobutyl swell, but the reverse was not possible, as indicated by the swelling volumes in the trimethylpentane. As displayed in Table II, attempts to use a highly symmetrically branched hydrocarbon with a very low solubility parameter, served only to reduce both the swelling of natural rubber and chlorobutyl. (Neopentane is a gas above 10°C and a solid below — 20°C). Therefore, for this report the use of differential solvents in the study of interfacial bonding in blends was limited to systems of Cl-butyl and cw-polybutadiene or SBR. 

The mixed-crystal system formed by indomethacin and saccharin (l,2-benzisothiazol-3(2H)-one-l,1-dioxide) has been used to evaluate the feasibility of using supercritical fluids as media for the design and preparation of new cocrystals [44]. In this work, the relative merits of supercritical fluid processes (i.e., cocrystallization with a supercritical solvent, supercritical fluid as anti-solvent, and the atomization and anti-solvent technique) were evaluated, as well as the influence of processing parameters on product formation and particle properties of the yields. It was reported that while the anti-solvent and atomization procedures yielded pure cocrystal products, only partial to no cocrystal formation took place when using the crystallization process. 

In a first approximation, the new methods correspond to the conventional solvent techniques of supported catalysts (cf Section 3.1.1.3), liquid biphasic catalysis (cf Section 3.1.1.1), and thermomorphic ( smart ) catalysts. One major difference relates to the number of reaction phases and the mass transfer between them. Owing to their miscibility with reaction gases, the use of an SCF will reduce the number of phases and potential mass transfer barriers in processes such as hydrogenation, carbonylations, oxidation, etc. For example, hydroformylation in a conventional liquid biphasic system is in fact a three-phase reaction (g/1/1), whereas it is a two-phase process (sc/1) if an SCF is used. The resulting elimination of mass transfer limitations can lead to increased reaction rates and selectiv-ities and can also facilitate continuous flow processes. Most importantly, however, the techniques summarized in Table 2 can provide entirely new solutions to catalyst immobilization which are not available with the established set of liquid solvents. 

Antigen Waxes, fatty alcohols, paraffins, hard fat Melt method, solvent technique [1]... 

Analyte Sample Solvent Technique or Detection Limit Remarks Ref. 

In summary, vinblastine is extracted from Catharanthus roseus plants with aqueous acid or with aqueous alcoholic-acid, isolating the alkaloids from the extracts by the usual precipitation and solvent techniques, followed by purifying by chromatography (usually on alumina oxide columns), vinblastine is then obtained (31). 

Fig. 15 (a) Emulsion/solvent technique TEM images of PLEA particles with (b) 10 and (c) 25 nm iron oxide (50%) particles in PLEA [49]... 

To overcome these limitations, HME technology offers some distinct advantages over traditional methods of encapsulation. Notably, HME is generally a solvent free (or minimal amount of solvent) technique, is cost efficient, entails a small equipment footprint, is a continuous (melting, mixing, and shaping) process, and is snitable for numerous matrix materials and encapsulants. 

The pharmaceutical industry is one which has developed a strong track record in the successful management of wastes, including solvents. Techniques exist which allow recovery efficiencies of well over 90% in terms of solvent usage. Pharmaceutical manufacturers have used thermal destruction as a responsible means for waste disposal when recovery is not economically credible. An uncontrolled drive to ever higher recovery rates would impose severe and unnecessary penalties upon the industry with negligible environmental benefits. 

The protein-polymer microcapsules can be obtained by supercritical anti-solvent techniques [8]. Homogeneous protein-polymer mixtures were contacted with supercritical carbon dioxide in order to produce microspheres with diameter ranging from 1 to 5 pm and containing around 80% of protein. Production of PLA microparticles containing insulin, lysozyme, and chemotrypsin is claimed. SAS crystallization of a pharmaceutical (naproxen) and a biodegradable poly(L-lactic acid) was reported [8]. The results from SAS studies showed very small spherical particles... 

---