Showing papers in "Journal of chromatography library in 1975"

Chapter 3 Techniques in Column Extraction Chromatography

Abstract: Publisher Summary This chapter discusses techniques in column extraction chromatography. It is the simplest and most effective way of achieving multistage extractive separations whenever multistage separation processes are needed. In many applications, especially in radiochemistry, column separation techniques are preferable to other separation methods because the equipment is simple and does not necessarily contain moving parts. Replacement of equipment and execution of separations can be done by remote handling techniques. The possibility of using a wide variety of extracting agents as stationary phases enlarges the number of separations that can be achieved. The chapter discusses the standardization of support material. Because the support material used in inorganic column extraction chromatography differs in chemical nature, adsorptive properties, and particle size, standardizing it is necessary to get reproducible results. The chapter also discusses the loading of the support material with a stationary phase.

Chapter 2 Correlation between Extraction Chromatography and Liquid-Liquid Extraction

Abstract: Publisher Summary This chapter describes the correlation between extraction chromatography and liquid–liquid extraction and explains the way in which liquid–liquid extraction and extraction chromatography are closely correlated practically as well as theoretically. On the basis of this correlation, almost all extraction systems used in solvent extraction can be applied to extraction chromatography; many problems are solved concerning the separation of elements that cannot be satisfactorily achieved by single-stage liquid–liquid extraction. Extraction chromatography is very effective for the separation of analogous elements and also for the clarification of complicated extraction systems, such as the extraction of Ru. Either solvent extraction or extraction chromatography can be effectively utilized as a means of preliminary investigation of the other method, and at the same time, a combined study of the results from the two methods makes the explanation of the extraction mechanisms easier. Because of the effectiveness of chromatography, all methods of separation used in solvent extraction can be tried in extraction chromatography as well.

Chapter 4 Stationary Phases in Extraction Chromatography

Abstract: Publisher Summary This chapter discusses stationary phases in extraction chromatography and describes their performance characteristics and effects upon the overall behavior of chromatographic columns. The chapter presents a systematic survey of the different compounds used in column chromatography and outlines their extraction behavior. The main performance characteristics of an extraction-chromatographic stationary phase may be collected within retention, selectivity, and physical stability. The chapter also presents a systematic survey of the extractants used as stationary phases, such as acidic extracts. Acidic extractants are organic compounds that have acid groups in their molecules. They are often called “liquid cation exchangers” because their behavior can be easily related to that exhibited by cation-exchange resins.

Chapter 13 Use of Cellular Plastics in Extraction Chromatography

Abstract: Publisher Summary This chapter discusses the use of cellular plastics in extraction chromatography. The basic idea of the application of cellular plastics as supports is that chromatographic adsorption, exchange and partition processes can be favorably influenced by giving an adsorbent a hollow spherical (cellular) form and affecting the adsorption on the internal surface of cells. This can be done by using solid, rigid or flexible open-cell-type foamed synthetic polymers as column fillings. The chemical and physical properties of cellular plastics are described in the chapter. Preliminary experiments on different cellular plastics commercially available (polyvinyl chloride, viscose, rubber, and polyurethane) showed that polyurethane foam was at that time most suitable for application as support in extraction chromatography. In all types of chromatographic techniques, column preparation is of prime importance. Column preparation is a very critical step; it is the one where reversed-phase art plays an important role. The application of foam-filled columns in some inorganic and radiochemical separations is also reviewed in the chapter.

Chapter 5 Inert Supports in Column Extraction Chromatography

Abstract: Publisher Summary This chapter discusses inert supports in column extraction chromatography. The supports are of great importance in partition chromatography; they help retain the stationary phase distributed as a thin film to accelerate the achievement of the equilibrium state between the aqueous and organic phases. An ideal support has to meet many requirements such as to display good wettability by the stationary phase and to retain it in sufficient amounts. The fixed phase must not tear off the support with the flow of the mobile phase. There is no ideal support for partition chromatography. There is not such a strong demand in connection with the quality of supports in the extraction chromatography of inorganic substances as in the gas–liquid or liquid–liquid partition chromatography of organic substances. The reason is that organic partition chromatography is usually applied to separate substances with only slightly different distribution coefficients so that all properties of the support that influence the broadening of the chromatographic peaks are of great significance in the separation. Conversely, extraction chromatography of inorganic substances only seldom involves the separation of elements with very similar properties.

Chapter 1 Theoretical Aspects of Extraction Chromatography

Abstract: Publisher Summary This chapter presents the theoretical aspects of extraction chromatography, which is a particular form of liquid–liquid column chromatography. Extraction chromatography couples the favorable selectivity features of the organic compounds used in liquid–liquid extraction with the multistage character of a chromatographic process. The method is now competing favorably with ion-exchange chromatography in many separation problems and is particularly advantageous when micro amounts are concerned as is the case with radiochemical separations. The difference between extraction chromatography and normal partition chromatography lies in the fact that in the process of partition, the solute molecules undergo little, if any, chemical change apart from association or proton exchange, while extraction involves the transfer of the initially ionic solute from water into an organic phase, which is most often accompanied by complex chemical changes involving many interactions and equilibria. The term “extraction chromatography” is generally used when the stationary phase is an organic liquid or organic solution and the mobile phase is an aqueous solution.

Chapter 8 Extraction Chromatography of Lanthanides

Abstract: Publisher Summary This chapter describes the extraction chromatography of lanthanides. The development of extraction chromatography as a method for the separation of inorganic ions is closely connected with the problem of the separation of lanthanides. Because of the similarity of their chemical properties, lanthanides represent a difficult analytical problem, and the ability to separate them is considered as a test for any new method aimed at the separation of ions. Any practical application of extraction chromatography to the separation of lanthanides requires the knowledge of some basic facts concerning the extraction of these elements using different extractants, particularly the knowledge of the magnitude of the separation factors for neighboring lanthanides in different systems. Lanthanides can and actually have been extracted by each of the three main extraction mechanisms: formation of chelate complexes with acidic extractants, solvation of salts, and formation of ion pairs.

Chapter 9 Extraction Chromatography of Fission Products

Abstract: Publisher Summary This chapter describes the extraction chromatography of fission products. Extraction chromatography is a useful means of solving various problems encountered in fission-product analysis. The chapter discusses problems in the main fields where the analysis, separation, isolation, purification, or characterization of fission products are required. In reprocessing analysis, extraction chromatography is used both for quantitative radiochemical analysis and for control of the extractability and chemical state of fission products and actinides in process solutions. For burn-up determinations, the method is used for preparing pure fractions of typical burn-up monitors. The method may also be used to isolate long-lived or stable fission products from waste solutions, environmental and biological samples. The high-separation factors achieved by multistage contacts facilitate the separation of minor amounts of fission products from macro concentrations of fissile materials.

Chapter 14 Laminar Techniques as an Aid in Planning Column Extraction Chromatographic Separations

Abstract: Publisher Summary This chapter describes the use of laminar techniques in planning column extraction chromatographic separations. Planning column separations in extraction chromatography involves a search for the best conditions to resolve a known mixture of elements. Speed and simplicity are the main advantages of laminar extraction chromatographic systems. They present the highest grade of flexibility, but because they work on small spots, they are severely limited when the separations of massive amounts of element or the recovery of the separated substances are required. The chapter discusses the correlations of laminar R f values to the distribution coefficients of the relevant liquid–liquid extraction system and the retention volumes of the corresponding chromatographic column. The principal features involved in planning a column separation from laminar R f spectra are discussed in the chapter.

Chapter 19 Phenols

Abstract: Publisher Summary In recent years, an important role in the separation of phenols and their derivatives has been played by gel chromatography on hydrophilic and organophilic gels, and in relatively polar solvents. The effects of the shape and size of the molecule and the effect of solvation of the phenolic hydroxyl group also influence the separation. The separation of phenols can also based on the fact that the phenolic hydroxyl group forms bonds with the amide group present in—for example, polyamide gels. The bond strength depends on the number and positions of the hydroxyl groups in the phenol molecule. The capacity of polyamides is usually relatively high, thus making these gels suitable for the separation of isomers. The eluotropic series of solvents used for the elution of phenols from a polyamide column is represented by water, ethanol, methanol, acetone, formamide, and dimethylformamide. With water, elution occurred according to the number of hydroxyl groups contained in the phenol.

Chapter 10 Mobile phases

Abstract: Publisher Summary In liquid–liquid chromatography, the fundamental process of distribution is based on dissolution. Hence, this technique may be looked upon as a repeated distribution of samples between two mutually immiscible liquids. The high efficiency of the distribution process may be achieved by a frequent repetition of the elementary distribution process affected by the movement of one liquid phase. The prerequisite for chromatographically utilizable sample retention in a liquid–liquid system is the achievement of a measurable concentration of solute in the mobile phase m and the stationary phase s. Deviations from the ideal behavior of the solute in solutions may be positive or negative and be of different magnitudes. In solutions, where only the weak interactions of molecules occur because of dispersion forces, the values of activity coefficients may be expressed in values close to unity. The main reasons for this are the inadequacy of the theory of solutions for giving an effective and sufficiently precise prediction of partition coefficients in any given system, a lack of data necessary for the prediction (molar volumes, critical temperatures and solubility parameters), and, to a certain extent, also the difficult calculations encountered.

Chapter 6 Fundamentals of ion-exchange chromatography

Abstract: Publisher Summary This chapter discusses the fundamentals of ion-exchange chromatography. Ion exchangers can be defined as polyvalent materials that are insoluble in water, contain bound ionogenic groups, and are capable of dissociating and exchanging ions in solution. Sometimes the shortened term ionex is used instead of ion exchanger. In spite of the fact that there are natural ion exchangers, most ion exchangers have been prepared synthetically. Ion exchangers and their properties have been described in thousands of papers and tens of monographs that deal with chromatographic aspects. In a typical ion exchanger, there are two main components—a porous matrix (or network) and electrically charged, covalently bound functional ionogenic groups. Ion exchangers can be divided into four main groups, depending on the composition of the matrix: (1) inorganic exchangers, based on aluminum silicates and other suitable minerals, (2) the synthetic resins of many types, (3) ion-exchange cellulose, and (4) ion-exchange polydextran.

Chapter 8 Instrumentation for liquid chromatography

Abstract: Publisher Summary This chapter discusses the instrumentation for liquid chromatography. The rapid development of the chemistry of natural products after the Second World War is directly connected with the utilization of chromatographic separation methods. The techniques of liquid chromatography play an important role in this development and form the basis of high-efficiency liquid chromatography. The extensive use of liquid column chromatography in the past has been evidently the result not only of the extension of the applicability of separation, analytical, and preparative methods but also of the simplicity and cheapness of chromatographic equipment. Currently, the classical procedures of column chromatography are still used predominantly and cannot be surpassed from the methodical point of view. More expensive fraction collectors sometimes have selectable regulation principles. Weight-regulated collectors have numerous disadvantages: the apparatus is sensitive to heating, the adjustment of balance is exacting, they often require vessels with identical weights, and they cannot be used if the density of the effluent changes.

Chapter 48 Pigments of plastids and photosynthetic chromatophores

Abstract: Publisher Summary Special, photosynthetically active pigments occur in the unique structural units of autotrophic plants and are present in the colored plastids (the chloroplasts) of higher plants and various algae. These special chloroplast pigments are divided into three principal groups: the green fat-soluble chlorophylls, the yellow fat-soluble carotenoids, and the red and blue water-soluble phycobilins. The separations of the natural mixtures of the pigments, mainly for their subsequent spectroscopic determination, usually depend upon differential solubility or differential sorption, properties that are related to the polarity of the pigments themselves. In principle, only fresh, turgid plant material should be analyzed, because storage may result in altered pigments. If the material cannot be analyzed immediately after sampling, storage at temperatures below 0°C for 1 or 2 days in polyethylene bags or rapid freezing in a mixture of acetone and dry ice or in liquid air or liquid nitrogen can be used.

Chapter 4 Physico-chemical basis of chromatographic retention in liquid — liquid and liquid — solid systems

Abstract: Publisher Summary This chapter discusses the physico-chemical basis of chromatographic retention in liquid–liquid and liquid–solid systems. The intrinsic sorption properties of the system are given by the chemical nature of the phases and are represented by the distribution constant. In this respect, the distribution constant can be considered as a most important chromatographic quantity. The distribution constant reflects equilibrium between the escaping tendencies that the solute exerts in the media of the stationary and the mobile phases. The escaping tendencies are determined by the disparities in solute–solute, solvent–solvent, and solute–solvent intermolecular interactions and can be characterized quantitatively in terms of the excess Gibbs free energy. As there is a simple relationship between the partial molar excess Gibbs free energy of the solute in a given solute–solvent mixture and the respective Raoult's law activity coefficient, the latter is also a suitable quantitative measure of the escaping tendency of the solute.

Chapter 16 Radiochromatographic techniques

Abstract: Publisher Summary This chapter discusses radiochromatographic techniques. The chromatography of radioactive substances is encountered in many fields, but especially in biochemistry and the biological sciences. In radiochemistry, chromatography is used for the isolation and analysis of the products of nuclear and chemical reactions. The chromatographic technique as such, involving sample introduction, columns, sorbents, developers, and a pumping system, is used for radioactive substances and does not differ in any essential respect from the techniques used for stable nuclides. The possibility that radioactive reaction products such as tritiated water from tritiated compounds and 14CO2 from 14C-labelled compounds may be generated should also be considered and atmospheric contamination avoided. Radiation detectors used during or after liquid column chromatography differ according to the type of involved radiation, its energy, and sometimes its level. The usual method for detecting γ-radiation involves the use of an aluminum-covered crystal of thallium-activated sodium iodide coupled to a photomultiplier.

Chapter 49 Macromolecular substances and plastics

Abstract: Publisher Summary This chapter discusses macromolecular substances and plastics. In industry, gel permeation chromatography (GPC) serves as a method for characterizing and analyzing new polymeric products and for controlling the quality of standard products (Harmon). Not only the method rapidly indicate out-of-specification batches but sometimes it can indicate directly the source of a particular problem, because the molecular-weight distribution directly reflects the conditions of preparation, either in polymerization or polycondensation reactions or in blending of polymer compositions from individual, pre-synthesized products. The telomeric compounds arising during the reaction are followed quantitatively by gel chromatography in tetrahydrofuran, owing to the good resolution of the gel. Modified dextran and acrylamide gels proved to be excellent materials for the separation of oligomeric mixtures in organic solvents. The gel chromatography of oligomers is widely used in the analysis of complex systems that arise during the preparation of various resins by polycondensation or polyaddition reactions.

Chapter 43 Boron compounds

Abstract: Publisher Summary The separation of rigid boron compounds is based on differences in the sizes and shapes of the molecules, in dipole moments, Bronsted or Lewis acidities, and in the characters of the substituents. In some instances, the use of liquid–solid chromatography is limited by the reactivity of the compounds to be separated toward water, air, or some solvents. However, a careful choice of chromatographic conditions can decrease this sensitivity to an acceptable level. Water- and air-stable borane compounds (most ligand derivatives, closo -carboranes, and metallocarboranes) are chromatographed on silica gel or aluminum oxide. Some of the air-sensitive boron compounds can be separated in an inert atmosphere on an activated and gas-free stationary phase. The chromatographic behavior of various carboranes is based on their dipole moments (dependent on the character of the skeleton, the location of heteroatoms, or the different locations of substituents) and on the character and number of substituents. Higher boranes and their substituted derivatives are mildly sensitive to air and show different sensitivities towards water and heat.

Chapter 22 Carbohydrates

Abstract: Publisher Summary The most suitable mobile phases for carbon column chromatography are water and aqueous alcohols, such as methanol, ethanol, n -butanol, and 2-butanol Taylor and Whelan reported that the pH of the eluting medium has a considerable effect on the manner in which sugars emerge from the column Nonpolar mono- and oligo-saccharides appear as sharper bands when the mobile phase is acidic than when it is neutral Many adsorbents have been used for the adsorption chromatography of sugars and their derivatives in the past three decades: charcoal, silica gel, alumina, Fuller's earth clays, calcium acid silicate, hydrated magnesium acid silicate, freshly precipitated calcium carbonate, etc (Binkley) Nowadays, chromatography on ion-exchange resins and gel permeation chromatography are of major interest and only the first three of the above adsorbents have retained their importance Chromatography on alumina is, in practice, not very different from the procedures used in for silica gel In comparison with silica gel, the chemical reactions of solutes on alumina columns occur more frequently In practice, there is always some partition effect owing to the partial solubility or adsorption of the compound in the resin matrix, and molecular sieve effects cannot be neglected

Chapter 12 Use of Extraction Chromatography for Trace Metal Preconcentration and Separation

Abstract: Publisher Summary This chapter describes the use of extraction chromatography for trace metal preconcentration and separation. In analytical chemistry, a number of techniques are available for the preconcentration of trace amounts of various elements, the most important being coprecipitation, ion-exchange, and liquid–liquid extraction. One of the most widely used methods is extraction, which may yield a fairly high enrichment. However, liquid–liquid extraction techniques do not usually provide a high degree of absolute preconcentration. The preconcentration of small amounts of impurities by ion-exchange has little been used for separating microtraces from large amounts of bulk material. In many cases, this type of analytical problem can be solved by the method of extraction chromatography. Extraction chromatography is suitable for the separation of elements with closely similar properties, and it is finding expanding application in various fields of radiochemistry, analytical chemistry, and nuclear technology. Extraction chromatography has mainly been applied to the quantitative separation of components present at comparable levels, but its multistep character also allows the separation of components present in micro to macro ratios with a simultaneous absolute preconcentration of a microcomponent.

Chapter 9 Sorbents

Abstract: Publisher Summary The choice of the mobile and stationary phases is determined by experience in the appropriate field of application, and it is usually limited to several well-established systems Therefore, it can be useful to consider the range of substances that may fulfill the function of the solvent or the sorbent and attempt to classify them more rationally based on their physical nature and function during chromatographic sorption By applying such approach, it can be seen that sharp boundaries among single types of phases(gas, liquid, and adsorbent) are removed, as is well known from chromatographic practice, and a continuous transition from gases up to solid substances does indeed exist A sufficiently compressed gas in the supercritical region already has the properties of a liquid, and this applies even more to a completely liquefied gas A similar continuous transition also occurs in the construction of porous materials from strictly geometrically regular networks of porous crystals to substances with random porosity

Chapter 34 Peptides

Abstract: Publisher Summary Methods for the separation of peptides can be classified according to the nature of the properties responsible for the separation. These properties are of five types: (1) molecular or particle weight of peptides (gel permeation chromatography), (2) net electric charge (ion-exchange chromatography), (3) difference in solubility in two phases (partition chromatography), (4) adsorptive forces (adsorption chromatography), and (5) highly selective affinity to different substances covalently bound to the solid matrix (affinity chromatography). Separations based on the net electric charge of the peptide depends on the formation of multiple electrostatic bonds between charged sites on the surface of the exchanger and the opposite charge sites of the peptide. The dipolar ionic character of the peptides allows the use of both cation and anion exchangers. The only restrictions are because of the limited solubility of peptides at different pH values. Nowadays, the ion-exchange chromatography of peptides is well developed, can be partially or fully automated, and is so versatile that it can be used for the separation of virtually any peptide mixture.

Chapter 20 Ethers and peroxides

Abstract: Publisher Summary Volatile ethers are analyzed by gas chromatography, because they are thermostable. However, other conditions for analysis have to be chosen for thermolabile substances, such as some types of peroxo compounds. The isolation of ethers and peroxides, their separation, and their determination in the reaction products or in commercial products are frequently necessary. The liquid column chromatography of ethers and peroxides is used predominantly for their purification and isolation; it is used less for analytical purposes. For the separation and the preparation of monodisperse polyethylene oxides, gel permeation chromatography can be used. Pure oligomers are isolated by this method on a preparative scale using a polystyrene gel cross-linked with 2% divinylbenzene. The adsorption of peroxides is dependent on the amount of water present in the adsorbent and in the solvents, which comprise the mobile phase.

Chapter 11 Chelating Agents as Stationary Phase in Extraction Chromatography

Abstract: Publisher Summary Chelating agents are mostly solid; therefore, they have to be used dissolved in appropriate organic solvents. In comparison with liquid extractants, the capacity of a stationary organic phase is smaller. After the evaporation of a solvent, the precipitation of a solid agent as well as of metal chelates can occur. The solvent extraction of metal chelates has some advantages compared to other types of extractants. The overall two-phase heterogeneous reaction can be described by relatively simple equations that relate the distribution ratio D with pH, the concentration of the extractant in an organic phase, and the concentration of masking agents in an aqueous phase. The chapter describes the influence of kinetic factors. Being a dynamic process, extraction chromatography is affected by the kinetics of extraction. Scarce information is available regarding the rate of extraction, particularly re-extraction processes.

Chapter 10 Use of Extraction Chromatography in Radiotoxicology

Abstract: Publisher Summary This chapter describes the use of extraction chromatography in radiotoxicology. Radiotoxicology is a new branch of science concerning the prevention and determination of internal contaminations from radioactive substances. When the contaminating radionuclide is a gamma or an X-ray emitter, a technique can be used that provides the direct determination of body burden by means of gamma spectre metric analysis on the contaminated subject; the complete apparatus is named “whole-body counter.” On the contrary, if the incorporated radionuclide is an alpha or a beta emitter, no direct method can be used, and the body burden can be calculated only by indirect methods taking into account the relation between the body burden and the excretion patterns of the contaminant. Periodical radiotoxicological analyses are carried out on the technical personnel exposed to a risk of internal contamination from radionuclides. Except for natural uranium and natural thorium, the final determination is made by counting the alpha or beta emitters previously separated from the urine. Features of radiotoxicological techniques for routine purposes are also discussed in the chapter.

Chapter 7 Affinity chromatography

Abstract: Publisher Summary Affinity chromatography is a technique for the isolation of biologically active substances, making use of their exceptional property of selective and reversible binding of other substances, for which Reiner and Walch introduced the term “affinant.” An affinant can, therefore, be considered as a special case of a ligand. In alkaline medium, chymotrypsin and trypsin form a complex with the bound trypsin inhibitor, thus separating from the inactive material that passes through the column unretained. In general, any compound is suitable for the isolation of biologically active substances that bind it specifically, firmly, and reversibly. Because of the widely varying character of biologically active substances, chemically affinants are also of very diverse types and their classification is, therefore, based on their biochemical function rather than on their chemical structure. For proteins binding vitamins, the corresponding vitamin serves as the affinant—for example, biotin for the isolation of avidin.

Chapter 21 Oxo compounds

Abstract: Publisher Summary Carbonyl compounds are most often separated in their hydrogen sulfite form by ion-exchange chromatography on basic resins. The use of liquid chromatography for the systematic separation of free aldehydes and ketones is not extensive. In the liquid chromatography of oxo compounds, their derivatization is also made use of; mainly oximes and 2,4-dinitrophenylhydrazones are prepared. The application of liquid chromatography in lignin chemistry is topical at present. Chromatographic papers in this field can be divided into two main groups. The first group deals with the fractionation of polydisperse lignin derivatives and the determination of the molecular-weight distribution on the dextran gel Sephadex. The second group, dealing with the separation of lignin derivatives (mainly ligninsulphonic acids), uses ion exchangers in which molecular sorption plays a role in addition to ion exchange. Liquid chromatography can be used for the determination of carbonyl compounds in the form of derivatives with hydroxylamine, and the oximes formed can be determined by ion-exchange chromatography.

Chapter 29 Terpenes

Abstract: Publisher Summary Terpenic compounds occur mainly as plant components and are often obtained by steam distillation in the form of essential oils. In addition to conventional extraction procedures or by the collection of the exudates of some shrubs and trees, some structurally less common terpenes or those which contain less common elements, for example bromine and chlorine, have also been found in animal and insect tissues and also as metabolites of moulds. For the separation of most terpenic hydrocarbons, silica gel or neutral alumina impregnated with silver nitrate and also activated alkaline alumina can be used; commonly used eluents are n-pentane, light petroleum fractions, or benzene, in some instances with the gradual addition of small amounts of diethyl ether (gradient elution). The solvents used for chromatography on such adsorbents should be freed from the traces of sulfur compounds, preferably by filtration through a small amount of the same adsorbent.

Chapter 24 Polysaccharide-protein complexes

Abstract: Publisher Summary There are two different approaches for the separation of anionic glycosaminoglycans (acid mucopolysaccharides) The most common technique in clinical analysis is based on the selective dissociation of cetylpyridinium complexes of these compounds in the solutions of different salt concentrations The chromatographic separations of glycoproteins are virtually indistinguishable from procedures used in protein and peptide chemistry In addition, there are a number of proteins that, in the usual sense, are not considered as glycoproteins though they carry one or several glycosidic residues On the other hand, there is a chromatographic procedure that is specific for the structural analysis of glycoproteins and glycopeptides; the specificity is based on the suitable arrangement of the detection system rather than on the separation procedure itself The complete reaction mixture passes through another mixing coil and enters into a heating bath in which the temperature of the mixture is increased to 96°C

Chapter 28 Steroids

Abstract: Publisher Summary Some steroid mixtures can be separated by several chromatographic methods that differ in principle. For example, a chemist isolating a small amount of a new or unknown steroid from a natural material involves a double task: first the elimination of ballast in a preliminary run (on a large amount of sorbent, but a shorter column) and then the required separation and purification on a small diameter but very long column. For the choice of the most suitable method for a particular separation problem in the steroid field, several criteria must be kept in mind: (1) scale—for example, the amount of the mixture to be separated, (2) proportions of the required or analyzed steroid or steroids in the mixture—for example, the number and amounts of components, (3) the physico-chemical character of the steroids to be separated—for example, polarity, solubility, etc., and (4) the structures of the steroids to be separated.