Coupling techniques

The following methods play a role in the commercial production of azo pigments  

The coupling component is dissolved in an alkaline solution and, after adding a clarifying agent and possibly charcoal to the solution, it is filtered through a sparkler filter or a filter press. 

The solution is then transferred into the coupling vessel equipped with a mechanical stirrer and, possibly in the presence of a surfactant, precipitated with acetic acid, hydrochloric acid, or phosphoric acid. The coupling component may also be precipitated indirectly i.e., the appropriate mixture of acid and emulsifier is filled into the kettle first and the alkaline solution of the coupling component is then added gradually to the clear solution by gravity flow. The clarified solution of the diazonium compound is then introduced into or onto this coupling suspension. 

Precipitating the coupling component with acetic acid or phosphoric acid often automatically provides the buffer that is necessary to maintain a certain pH throughout the coupling reaction. Otherwise, buffers such as sodium acetate, sodium phosphate, or calcium carbonate ( chalk coupling ) must be added. 

The clarified acidic diazonium salt solution is first transferred to a coupling vat equipped with a mechanical agitator, and the clarified alkaline coupling component solution is then added above or under the surface of the diazonium salt solution. Constant agitation is essential. 

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Samples containing mixtures of peptides can be analyzed directly by electrospray. Alternatively, the peptides can be separated and analyzed by LC/MS coupling techniques such as electrospray or atmospheric pressure chemical ionization (APCI). 

In this present chapter, the applications of multidimensional chromatography using various types of coupled techniques for the analysis of industrial and polymer samples, and polymer additives, are described in detail. The specific applications are organized by technique and a limited amount of detail is given for the various instrumental setups, since these are described elsewhere in other chapters of this volume. 

An on-line supercritical fluid chromatography-capillary gas chromatography (SFC-GC) technique has been demonstrated for the direct transfer of SFC fractions from a packed column SFC system to a GC system. This technique has been applied in the analysis of industrial samples such as aviation fuel (24). This type of coupled technique is sometimes more advantageous than the traditional LC-GC coupled technique since SFC is compatible with GC, because most supercritical fluids decompress into gases at GC conditions and are not detected by flame-ionization detection. The use of solvent evaporation techniques are not necessary. SFC, in the same way as LC, can be used to preseparate a sample into classes of compounds where the individual components can then be analyzed and quantified by GC. The supercritical fluid sample effluent is decompressed through a restrictor directly into a capillary GC injection port. In addition, this technique allows selective or multi-step heart-cutting of various sample peaks as they elute from the supercritical fluid... 

Important developments in LC-GC have been made by Grob and co-workers (79-81) and by the Brinkman group (82-87), who have mainly studied the application of this technique to environmental analysis. This coupled technique has usually been applied to water, although air and soil extracts have also been analysed. 

The on-line principle has also been extended into the field of detection (Fig. 8). Thus, it is now possible to record FTIR [27-31] and Raman spectra in situ [32, 33], and there have been considerable advances in the on-line coupling of thin-layer chromatography with mass spectrometry. Here it has been, above all, the research groups of Wilson [34-36] and Busch [37-40] that have made the necessary instrumental and methodological advances, so that TLC must no longer be viewed as merely a clean-up method. Rather it forms the essential central point for all these on-line coupling techniques. 

Documentation is carried out as soon as the iodine-colored chromatogram zones can be readily recognized. Then the adsorbed iodine can be allowed to evaporate in the fume cupboard or vacuum desiccator, so that the same chromatograms can be subjected to further reactions and separation steps (e. g. SRS techniques, 2-D separations, coupling techniques such as TLC/GC etc.). The chromatogram zones can also be stabilized by spraying with 0.5 to 1 percent starch solution [4, 5] the well-known blue clathrates that are formed (starch-iodine inclusion compounds) remain stable for months. 

Principles and Characteristics SFC-MS is a sensitive coupled technique that can be selective or universal it was first mentioned in 1978 [396]. Further developments are given in Table 7.36. It is used in an on-line mode with open cell gas-phase interfaces, where the mobile phase is decompressed to low pressures. SFC presents a number of features which allow for easier coupling with MS than other chromatographies. In practice, however, SFC-MS coupling did not turn out to be as easy as expected, a fact which can be ascribed to the problems met in the adiabatic expansion of the mobile phase and the effects of pressure gradients in the ion... 

While most preliminary SFC-plasma coupled techniques employed microwave-induced plasmas (MIPs), the use of ICP-MS is now increasing [469]. An advantage of microcolumn SFC-ICP hyphenation is the significantly reduced flow-rates of microcolumns compared with those of conventional columns. Both pSFC-ICP-AES [470,471] and cSFC-ICP-AES [472] were described. In the case of elemental detector selectivity (e.g. AES) complete chromatographic resolution is not required. The detector possesses linearity over several orders of concentrative magnitude. Minimum detectable quantities for nonmetals range from sub to low ng mL"1. 

Second, dopamine has been linked covalently to a poly(aryloxy-phosphazene) via a diazo-coupling technique (24). Experiments showed that rat pituitary cells in culture responded to the surface-bound dopamine in a similar manner to that found when the dopamine was free in solution. 

Zhang et al. [49] determined penicillamine in urine by the coupled technique of chemiluminescence detection and liquid chromatography. The urine sample was adjusted to pH 2 with 2 M H2S04 and centrifuged at 3000 rpm for 5 min. A 12 mL... 

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