Application Synthetic Dyes

Azo compounds have two important applications as dyes and as sulfa drugs, the first synthetic antibiotics (Section 25.17). 

Until 1856, all dyes were natural in origin, obtained from plants, animals, or minerals. Three natural dyes known for centuries are indigo, tyrian purple, and alizarin. 

The blue dye indigo, derived from the plant Indigofera tinctoria, has been used in India for thousands of years. Traders introduced it to the Mediterranean area and then to Europe. Tyrian purple, a natural dark purple dye obtained from the mucous gland of a Mediterranean snail of the genus Murex, was a symbol of royalty before the collapse of the Roman empire. Alizarin, a bright red dye obtained from madder root Rubia tinctorum), a plant native to India and northeastern Asia, has been found in cloth entombed with Egyptian mummies. 

Because all three of these dyes were derived from natural sources, they were difficult to obtain, making them expensive and available only to the privileged. This all changed when William Henry Perkin, an 18-year-old student with a makeshift home laboratory, serendipitously pre- 

A purple shawl dyed with Perkin s mauveine 

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The synthetic dye industry is well over 100 years old with manufacture and application of dyes being carried out globally. Environmentally, the... 

In the food industry, synthetic dyes can be used also in the form of lakes obtained by precipitation of a soluble colorant onto an insoluble base. There are several insoluble bases, but only alumina is permitted for food application by FDA and EU regulation. All the synthetic food dyes can be obtained and used in food in the form of aluminium lakes, except erythrosine due to concerns about inorganic iodine content. 

Major applications of modern TLC comprise various sample types biomedical, pharmaceutical, forensic, clinical, biological, environmental and industrial (product uniformity, impurity determination, surfactants, synthetic dyes) the technique is also frequently used in food science (some 10% of published papers) [446], Although polymer/additive analysis takes up a small share, it is apparent from deformulation schemes presented in Chapter 2 that (HP)TLC plays an appreciable role in industrial problem solving even though this is not reflected in a flood of scientific papers. TLC is not only useful for polymer additive extracts but in particular for direct separations based on dissolutions. 

Capillary HPLC-MS has been reported as a confirmatory tool for the analysis of synthetic dyes [585], but has not been considered as a general means for structural information (degradant identification, structural elucidation or unequivocal confirmation) positive identification of minor components (trace component MW, degradation products and by-products, structural information, thermolabile components) or identification of degradation components (MW even at 0.01 % level, simultaneous mass and retention time data, more specific and much higher resolution than PDA). Successful application of LC-MS for additive verification purposes relies heavily and depends greatly on the quality of a MS library. Meanwhile, MB, DLI, CF-FAB, and TSP interfaces belong to history [440]. 

Husain Q (2006) Potential applications of the oxidoreductive enzymes in the decolorization and detoxification of textile and other synthetic dyes from polluted water a review. Crit Rev Biotechnol 26 201-221... 

It has been stated that the global LSER equation (eq. 1.55) takes into consideration simultaneously the descriptors of the analyte and the composition of the binary mobile phase and it can be more easily employed than the traditional local LSER model [79], The prerequisite of the application of LSER calculations is the exact knowledge of the chemical structure and physicochemical characteristics of the analyses to be separated. Synthetic dyes as pollutants in waste water and sludge comply with these requirements, therefore in these cases LSER calculations can be used for the facilitation of the development of optimal separation strategy. 

Organic modifiers have been frequently employed in CE to increase the solubility of hydrophobic solutes in the aqueous buffer system. Unfortunately, many organic modifiers are UV absorbent and cannot be used without considerable loss of sensitivity of detection. A contactless conductivity detection system has been developed which extends the application range of UV-absorbing solvents [ 119]. As both natural pigments and synthetic dyes absorb in the visible part of the spectra, the application of UV-absorbing organic modifiers in their CE analysis does not cause detection problems. 

The application of an organic solvent in CE offers a new possibility to change the selectivity of CE systems. Moreover, the various ion-solvent interactions and ion-pair formations can be exploited for increased separation efficacy. Its application for CE analysis of ionic synthetic dyes may be expected in the future [121],... 

Ponceau 4R, E-124 and Erythrosine, E-127) using a buffered mobile phase. Separation of dyes was performed in an ODS column (150 X 3.9 mm i.d. particle size 3 pm). Components of the mobile phase were methanol (eluent A) and 0.1 M NaH2P04/Na2HP04 buffer (pH = 7). The gradient elution started with 20 per cent A and reached 100 per cent in 2 min, final hold 4 min. The flow rate was 2 ml/min and dyes were detected at 520 nm. The baseline separation of dyes in 6 min is illustrated in Fig. 3.34. Commercial samples were diluted and injected into the analytical column without any pretreatment. The amounts of dyes found in the samples are compiled in Table 3.20. It was concluded from the good validation parameters that the technique is specific, sensitive, accurate and rapid. Consequently, its application for the determination of these synthetic dyes in drinks was proposed [112],... 

The application of liquid chromatography-atmospheric pressure ionization-mass spectrometry in water analysis has been previously reviewed. The application of this technique for the analysis of synthetic dyes was also discussed [118]. 

The legal or illegal application of synthetic dyes in foods and food products increases consumer acceptance, and consequently, the profit of the producer. As a considerable quantity of foods and food products contain dyes, their determination is of considerable importance. Electrophoretic techniques have been frequently employed for dye analysis. Thus, micellar electrokinetic capillary chromatography has also been employed for the determination of synthetic colours in soft drinks and confectioneries [183],... 

Applications. Phthalic anhydride is used largely to make plasticizer for polyvinyl chloride. It is also a feed for alkyd resins and. for unsaturated polyesters that are widely used in construction, rharine, and synthetic marble applications. Other minor applications are dyes, esters, drying oil modifiers and pharmaceutical intermediates. 

This chapter has concentrated on the photochemistry, photophysics, and numerous applications of the hydroxyxanthenes, among the most versatile of the synthetic dyes. The literature concerning Rose Bengal seems to have grown most rapidly in recent years, in large measure because of its numerous applications. As we have studied these systems over many years, we find that their chemistry is rational, though complicated, and their spectroscopy, rich with information, is rewarding. We have tried to cover the subject broadly, but there is no possibility that we could do so exhaustively. We hope that readers will bear that in mind, and share additional information about the xanthenes and related systems with us as it comes to their attention. 

Anthraquinone vat dyes have been used to dye cotton and other cellulose fibers for many decades. Despite their high cost, relatively muted colors, and difficulty in application, anthraquinone vat dyes still form one of the most important dye classes of synthetic dyes because of their all-around superior fastness. 

Dyeing Mechanism. Nylon i.s. similar in its general chemical structure to the natural fiber wool, and therefore all the previously described processes lor wool are applicable to dyeing nylon with acid, metallized, and other dyes. There are. however, significant differences. Nylon is synthetic, it has delined chemical structure depending on the manufacturing process, and it is hydrophobic. 

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