Separations based on chemical

R. S. DeWitte, M. McBrien, and E. Kolovanov, Intelligent optimization of HPLC separations based on chemical structures benefiting from unified knowledge base, presentation by Advanced Chemistry Development,Toronto, Canada, March 5-8, 2001, New Orleans, Pittcon 2001. 

Typical HPLC/UV methods require that each analyte component separate during the chromatographic run. Analytes are separated (i.e., baseline separation) based on chemical interaction with the stationary phase and mobile phase. A unique retention time is generally required for each analyte and provides the basis for identification and comparative results. 

Separation Based on Chemical Potential Difference (Concentration Gradient)... 

The lowest feed concentration allowing economical recovery with these conventional processes is 3-5% w/w acetic acid, depending on the value accorded to recovered acetic acid. For more economical processing of dilute feed streams, a solvent giving a higher value of Kd is needed. This leads to chemical complexation. Acetic acid in these aqueous streams meets all the criteria listed abo.ve (Lewis-acid fiinctional group, low concentration, low volatility, and low activity coefficient in water) for solutes which are good candidates for separations based on chemical complexation. 

Multistep procedures are even more indispensable in the analysis of organic substances, where a chromatographic separation is often closely coupled with the actual method of determination, such as IR or mass spectrometry. Separations based on chemical reactions designed to generate new phases for subsequent mechanical isolation (e.g., precipitation, liquid-liquid partition) have also not been completely supplanted in elemental and molecular analysis. 

It is usually more convenient to employ a method of separation based on chemical reaction with a reagent, but in some cases fractional distillation is the only suitable procedure. It should be remembered that a satisfactory separation by distillation is unlikely if the boiling points of the components differ by less than about 25 C. Azeotropic mixtures are not separable by simple distillation. 

The product may be biomass itself, an organic molecule which is an excreted secondary metabolite or a complex protein which is accumulated within parts of the microbial cells. Consequently there are many ways by which products are extracted and purified. However, water removal, biomass removal and further separations based on chemical and ionic properties are usually employed to produce a crude product which may be further refined and subjected to chemical conditioning before the final product is realized. 

The same chemical separation research was done on thorium ores, leading to the discovery of a completely different set of radioactivities. Although the chemists made fundamental distinctions among the radioactivities based on chemical properties, it was often simpler to distinguish the radiation by the rate at which the radioactivity decayed. For uranium and thorium the level of radioactivity was independent of time. For most of the radioactivities separated from these elements, however, the activity showed an observable decrease with time and it was found that the rate of decrease was characteristic of each radioactive species. Each species had a unique half-life, ie, the time during which the activity was reduced to half of its initial value. 

DOSY is a technique that may prove successful in the determination of additives in mixtures [279]. Using different field gradients it is possible to distinguish components in a mixture on the basis of their diffusion coefficients. Morris and Johnson [271] have developed diffusion-ordered 2D NMR experiments for the analysis of mixtures. PFG-NMR can thus be used to identify those components in a mixture that have similar (or overlapping) chemical shifts but different diffusional properties. Multivariate curve resolution (MCR) analysis of DOSY data allows generation of pure spectra of the individual components for identification. The pure spin-echo diffusion decays that are obtained for the individual components may be used to determine the diffusion coefficient/distribution [281]. Mixtures of molecules of very similar sizes can readily be analysed by DOSY. Diffusion-ordered spectroscopy [273,282], which does not require prior separation, is a viable competitor for techniques such as HPLC-NMR that are based on chemical separation. 

Exclusion chromatography is also useful in the separation of small molecules from interfering matrices of larger molecules, for example in foods or other samples of biological origin. It can be used as the first step in the sequential analysis of complex unknown organic mixtures, which are first separated on a size basis by exclusion, then the collected fractions can be further separated by normal or reverse phase chromatography, where the separation is based on chemical differences. 

Seven groups of these drugs can be separated based on their various chemical f structures (a) lysergic acid derivatives, of which lysergide (LSD) is the prototype (b) phenylethylamine derivatives, of which 3,4,5-trihydroxyphenylethylamine (mescaline) is the prototype (c) indolealkylamines, such as 4-phosphorodi-methyltryptamine (psilocybin) (d) other indolic derivatives, such as the harmine... 

Newer and more complex humus extractions have been developed. These typically involve more steps such as both physical separation on the basis of density and particle size (related to the size of soil inorganic components), and chemical separation based on extractions and washings with hydrofluoric acid (HF), hydrochloric acid (HC1), and sodium hydroxide (NaOH). The products of such separations are then subjected to spectroscopic analysis and interpretation [22,23],... 

A vast number of polymer compounds are available commercially. Generally they are known by their polymer type in full or abbreviated (e.g., acrylic, polyvinyl chloride or PVC, high density polyethylene or HDPE), and frequently by a manufacturer s trade name. There is little standardisation into classes based on chemical composition or physical performance, as there is for metals. In reality, a particular chemical composition does not fully define the physical properties, while each class of performance properties can be met by a range of competing polymer types. The current trend is towards further diversification polymer compounds are increasingly being tailored to a particular application. Only in industries where recycling is an issue is there pressure for a more limited number of polymers, which can be identified and separated at the end of product life. 

The purpose of this paper is to describe the various types of separators based on their applications in batteries and their chemical, mechanical and electrochemical properties, with particular emphasis on separators for lithium-ion batteries. The separator... 

Morphology based on chemical environment can be probed using F NMR spectroscopy because the chemical shifts of F atoms in the side chains are considerably separated from those in the backbone. Conformational dynamics as affected by domain-selective solvent incorporation are reflected in the widths of static F peaks. These conformational motions, in turn, can influence the migration of solvent penetrants. 

It is our intention to present strategies based on chemically induced phase separation (CIPS), which allow one to prepare porous thermosets with controlled size and distribution in the low pm-range. According to lUPAC nomenclature, porous materials with pore sizes greater than 50 nm should be termed macroporous [1]. Based on this terminology, porous materials with pore diameters lower than 2 nm are called microporous. The nomination mesoporous is reserved for materials with intermediate pore sizes. In this introductory section, we will classify and explain the different approaches to prepare porous polymers and to check their feasibility to achieve macroporous thermosets. A summary of the technologically most important techniques to prepare polymeric foams can be found in [2,3]. 

In conventional continuous-flow configurations [2,3], (bio)chemical reactions, separations based on mass transfer between two phases, and continuous detection occur at different places and hence sequentially. 

In this chapter a process is described that can alleviate some of the difficulties described above. The technique is based on chemical reactions in aerosols (6). Specifically, droplets of a reactant flowing in an inert carrier gas are contacted with the vapor of a coreactant, resulting—as a rule—in spherical solid particles. If the latter are internally chemically mixed, their composition is determined by the contents of the reactants in the original droplets, since each of the latter acts as a separate reaction container. ... 

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