Older Techniques

The cupellation method is described in Chapter 6 Silver. In earlier times this separated gold from less noble metals such as lead, tin, iron and zinc. Any silver present, however, remained with the gold. 

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Miscellaneous. Electron beams can be used to decompose a gas such as silver chloride and simultaneously deposit silver metal. An older technique is the thermal decomposition of volatile and extremely toxic gases such as nickel carbonyl [13463-39-3] Ni(CO)4, to form dense deposits or dendritic coatings by modification of coating parameters. 

In contrast to the older techniques, a newer method is to use a scanning tuimeling electron microscope to deposit metal coatings in microscopic images as small as 0.001 pm. The ultimate surface metallization techniques allow deposition of metals atom by atom in controlled three-dimensional arrays. 

The older technique for this purpose (Ref 8), variously referred to as the paraffin test, the paraffin-glove test, the dermal nitrate test, and the diphenylamine test, had been abundantly shown to be unreliable, was no longer accepted in most US courts, and was now seldom used by good crime investigation laboratories... 

In this chapter, we describe some of the more widely used and successful kinetic techniques involving controlled hydrodynamics. We briefly discuss the nature of mass transport associated with each method, and assess the attributes and drawbacks. While the application of hydrodynamic methods to liquid liquid interfaces has largely involved the study of spontaneous processes, several of these methods can be used to investigate electrochemical processes at polarized ITIES we consider these applications when appropriate. We aim to provide an historical overview of the field, but since some of the older techniques have been reviewed extensively [2,3,13], we emphasize the most recent developments and applications. 

Retrogradation is another important property of starch. It is generally accepted that retrogradation is involved in the staling of baked products such as bread. In particular it appears that retrogradation is the recrystallisation of the amylopectin present. Notably, retrogradation is still a subject of research. The application of techniques such as 13C NMR allows insights that older techniques do not provide. 

These problems have largely been solved by the development of a wide variety of powerful LC-MS interfaces (reviewed in Refs. [1-3]). In the following paragraphs, the two most widely used atmospheric pressure ionisation (API) systems, namely atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI), are briefly described, along with the older technique of thermospray ionisation... 

Since all the physical properties of two given enantiomers are the same in the absence of a chiral, or optically active, medium, their chromatographic resolution needs a different approach from the relatively simple separation of geometrical isomers, stereoisomers or positional isomers. Two methods are used. The older technique of indirect resolution, requires conversion of the enantiomers to diastereoisomers using a suitable chiral reagent, followed by separation of the diastereoisomers on a non-chiral GC or LC stationary phase. This technique has now been largely superseded by direct resolution, using either a chiral mobile phase (in LC) or a chiral stationary phase. A variety of types of chiral stationary phase have been developed for use in GC, LC and SFC(21 23). 

Routine analyses of large numbers of similar samples can readily be automated and the sample throughput considerably increased (sometimes up to about 200 samples per hour) by carrying out the analyses in a continuously flowing medium. At present there are two basic approaches to the problem, the older technique of continuous-flow analysis (CFA) introduced more than 25 years ago [145] and widely developed by the Technicon Company (Auto-Analyzer), and more recent flow-injection analysis (FIA for a recent literature review see [123]). For a brief comparative survey of the two methods see [148]. 

The oxidation of both aliphatic and aromatic azo compounds to the corresponding azoxy derivative may be carried out with a variety of reagents. While older techniques favored chromic or nitric acid as the oxidizing agent, newer methods make use of various organic peracids or hydrogen peroxide. In the oxidation of aliphatic azo compounds, relatively weak peracids are favored to reduce the possibility of acid-catalyzed isomerization of azo compounds to hydrazones. Under controlled conditions cis azo compounds may be converted into cis azoxy compounds. 

A major recent innovation has been to use substrates that are unreactive but may be activated by, for example, photolysis (see Chapter 6). This has necessitated the introduction of crystallographic procedures that can gather data in fractions of a second, rather than the minutes or hours conventionally used. Conventional protein crystallography uses a beam of monochromatic x-rays. An older technique that has been reintroduced is that of von Laue, which uses a spectrum of polychromatic radiation. An intense beam from a synchrotron, spanning wavelengths from 0.25 to 2.5 A, enables data for the Laue method to be taken over a fraction of a second.46,47... 

Some very important surface properties of solids can be properly characterized only by certain wet chemical techniques, some of which are currently under rapid improvement. Studies of adsorption from solution allow determination of the surface density of adsorbing sites, and the characterization of the surface forces involved (the energy of dispersion forces, the strength of acidic or basic sites and the surface density of coul-ombic charge). Adsorption studies can now be extended with some newer spectroscopic tools (Fourier-transform infra-red spectroscopy, laser Raman spectroscopy, and solid NMR spectroscopy), as well as convenient modern versions of older techniques (Doppler electrophoresis, flow microcalorimetry, and automated ellipsometry). 

Closely related to DSC is the much older technique of differential thermal analysis (DTA). DTA works on the simpler principle of measurement (via thermocouple) of temperature difference between a sample and reference as the same heating power is supplied to both. The DTA trace therefore represents a temperature effect, which is related only semiquantitatively to AH. A combined DTA-TGA trace for the Werner clathrate (Section 9.4) [Ni(NCS)2(4-phenylpyridine)4] CgHg is shown in Figure 9.22. The DTA trace shows that all three thermal events observed are endothermic. The first is associated with loss of the benzene guest, while the second and third relate to loss of the coordinated 4-Phpy ligands. Note the high temperature (about 350 °C) required to remove the enclathrated benzene. This is a clear indication of the thermal stability of the Werner clathrate family.18... 

The issue is that the pediatrician at the bedside needs to understand more about rare disorders that he/she may never have encountered or have encountered only rarely in their entire clinical experience. The laboratory with the newest technology is required to explain the meaning of lab results, their reliability, and what changed in the methods and the results from older techniques. One of the biggest problems in newborn screening has been the falsepositive results that are often seen and, if sufficiently high, a cry wolf ... 

Several techniques have been developed that enable the number of hydrogens attached to the carbon to be determined. An older technique, called off-resonance decoupling, allows hydrogens and carbons that are directly bonded to couple but removes any longer-range coupling. In an off-resonance decoupled spectrum, a CH3 appears as... 

The calorimeter method is an older technique which is a direct measurement of Fourier s law. It is one of the ASTM [2] standard tests for thermal conductivity, designation C201. The experimental configuration is shown in Figure 9.3. A SiC slab... 

Virtually, all students of chemistry, biochemistry, pharmacy and related subjects learn how to deduce molecular structures from nuclear magnetic resonance (NMR) spectra. Undergraduate examinations routinely set problems using NMR spectra, and masters and doctoral theses describing novel synthetic or natural products provide many examples of how powerful NMR has become in structure elucidation. Existing texts on NMR spectroscopy generally deal with the physical background of the newer and older techniques as well as the relationships between NMR parameters and chemical structures. Very few, however, convey the know-how of structure... 

Finally, it should be noted that it is possible to overreact to new technology. The constant onslaught of new techniques and apparatus can be fascinating, and the temptation to switch to the latest (and trendiest) thing can be strong. However, the ultimate goal of answering evolutionary questions must be kept in mind, and the value of older techniques should not be underestimated. The real issue is how well a particular approach addresses the problem at hand. Sometimes an older, more mundane technique actually provides a better solution than the latest innovation. Many of the currently available techniques are likely to provide reliable, cost-effective approaches to questions of evolutionary interest for years to come. 

It is clear then that the chemical flame is an effective means by which a free, neutral atom population may be produced from a sample solution for analysis by atomic absorption spectrometry. The fact that flames were inherited from the older technique of flame emission spectrometry may account in part for their popularity, although they also have the following advantages for use in AAS ... 

Shortly before the successM preparation of organomag-nesium compounds by Victor Grignard, his mentor, Philippe Barbier, had discovered that reaction of an aldehyde or ketone and an alkyl hahde in the presence of magnesium metal led to formation of an alcohol, essentially as in the Grignard reaction . The use of the older technique, referred to as the Barbier method or as the in situ reaction, holds advantages in some cases. ... 

An analogous (older) technique is known as differential thermal analysis (DTA), which yields the same information as DSC. 

The basic techniques used in the purification of protein drugs have been developed in biochemical laboratories over the past several decades. However, the objectives of protein purification as applied to rDNA products differ from those encountered in the basic research laboratory. Purity of the final product is one of the objectives that is shared by protein purification processes in both situations. An objective critical in the purification of protein drugs is the clinical safety of the final product. In addition, the commercial nature and the scale of the protein pharmaceutical enterprise make cost another objective of great importance (Heinrikson and Tomasselli, 1991). This has led to the adaptation of older techniques to production scales as well as the development of newer methods. 

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