Application of synthetic dyes

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],... 

Synthetic dyes are extensively used in many up-to-date industrial processes and research, mainly in the preparation of textile, food, and leather products, as well as in cosmetics and medicine. The widespread application of synthetic dyes has resulted in serious environmental pollution Their occurrence in ground water and waste-water and the accumulation in sediment, soil, and various biological tissues has often been observed and reported. Dyes and intermediates can cause abnormal reproductive function in males and show marked toxic effects toward bacteria. The rate of biodegradation of the majority of synthetic dyes is very low, enhancing the toxicological hazard and environmental impact. 

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]. 

When scouring synthetic fibres that are to be dyed with disperse dyes, nonionic scouring agents are best avoided unless they are formulated to have a high cloud point and are known not to adversely affect the dispersion properties of the dyes. Conversely, when scouring acrylic fibres, anionic surfactants should be avoided [156] because they are liable to interfere with the subsequent application of basic dyes. These fibres are usually scoured with an ethoxylated alcohol, either alone or with a mild alkali such as sodium carbonate or a phosphate. 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

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]. 

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. 

The application of ion-pair HPLC in the analysis of food colors is summarized on Table 8. As indicated, TBA has been the most widely used ion pair. It can be observed that using gradient mobile phase elution, a larger number of synthetic dyes can be separated. However, the mobile phase programming should include a return to the initial condition as well as reequilibration of the column by maintaining the initial composition for a period of time. This procedure provides reproducible result (222). 

The development of the synthetic dye industry led to the emergence of classical organic chemistry. Its application in industry was rapid. From the end of the nineteenth century the intermediates employed in the manufacture of synthetic dyes were used to make pharmaceutical products such as aspirin. Some synthetic dyes exhibited bactericidal properties they were called medicinal dyes. Sulfonamides, drugs introduced in the 1930s, are based on research into dyestuffs and their intermediates. Less fast dyes have... 

Commercial synthetic dyes generally contain more than one color product. As the knowledge of the exact composition of dye mixtures is prerequisite for their successful application in many fields of industry and research, many efforts have been devoted for the development of various chromatographic techniques suitable for their separation and quantitative determination. Moreover, the exact determination of the composition and quantity of synthetic dye is required in the control of industrial processes, in the following of efficacy of wastewater treatment, in environmental protection studies, and in forensic science. 

It can be concluded from the present state of the art of TLC analysis of synthetic dyes that the methods are mainly limited to the application of traditional TLC technique. Due to the rapidly developing instrumentation and automation of the various steps of TLC analysis and the introduction of coupled methods (TLC-... 

Studies involving bile salts in EKC separations include (i) determination of i -triazines and quats in well water samples (ii) separation of the 16 priority pollutant PAHs for inspection in ambient air samples (iii) characterization of the electrophoretic behavior of 56 aromatic compounds (phenoxy acid herbicides, phenylalkanoic acids, aromatic carboxylic acids, aromatic sulfonic acids, azo and other dyes, and nitrogen-containing aromatic acids) for further assessment of extraction and sample clean-up procedures using spiked water and soils and (iv) recovery of synthetic dyes from spiked water and soil matrices. Another interesting application of MEKC with diverse bile salts is the prediction of ecotoxicity of aromatic compounds. ... 

CZE separation of synthetic dyes has been approached by simple (borate and citrate) and volatile buffers (ammonium acetate) modified by solvents as well as nonaqueous systems (ammonium acetate/acetic acid in MeOH). Environmental applications of CZE methodologies include the analysis of spent dyebaths and wastewater samples and the monitoring of groundwater migration, where eosin was used as a fluorescent tracer (details in Table 31.8). ... 

This entry succinctly presents the application of high-speed countercurrent chromatography (HSCCC) in its various forms to the separation and purification of synthetic dyes used in food, drugs, and cosmetics. 

There are two notable advantages of using this technique for the separation of synthetic dyes. First, it is applicable to the separation of both ionic and non-ionic components of a dye mixture. Second, it has been shown to be one of the best methods for successfully separating small quantities (20 mg or less) of dye mixtures. On the contrary, several hundred milligrams is the upper limit beyond which conventional HSCCC cannot be used for separating dye mixtures. Two examples of the application of this technique are shown in Figs. 2 and 3. Fig. 2 shows... 

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