Colours synthetic

Synthetic colours are materials based around azo-sulphonic acids. They are water soluble and provide strong stable colours. There is an interesting chapter by Wadds (1984) that discusses some of the basic methods, including thin-layer, paper and high-performance liquid chromatography, which have been used in the past and are still used today to analyse for these colours. 

When colours are added to a food system, their characterisation is often more difficult due to interferences from other materials in the food or difficulty with their extraction from the food. This is particularly the case for high-protein foods, which bind colours very tightly and can make their quantitative analysis very difficult. However, analysis for azo-dyes in soft drinks is generally straightforward using modern methods. There is less interference than in other food systems and as the colours are already in solution, and not bound to other materials, this makes the analysis easier. In some cases, the colours can be analysed without prior concentration and in others they have to be concentrated by solid-phase extraction methods, for example, Ci8 cartridges followed by elution with a small volume of methanolic ammonia. 

Owing to the varied structures of various food dyes, they can often be differentiated from one another by their characteristic ultraviolet/visible absorbance spectra. Using HPLC coupled with a diode array detector (HPLC-DAD) it is possible to collect a compound s absorbance spectrum as it elutes from the HPLC column, which greatly assists in identification. At Reading Scientific Services Ltd (RSSL) this type of detector is routinely used in a range of analyses of such substances as patulin, a mycotoxin found in apple juice, and in the analysis of colours and vitamins, which allows a more certain assignment of a particular peak to a specific compound to be made. 

A number of different approaches, all of which have both advantages and shortcomings, have been proposed for the analysis of water-soluble dyes. The separation of colours has been carried out using ion-exchange resins, reverse-phase HPLC coupled with ion-pair reagents and reverse-phase HPLC at low pH where the ionisation of the dyes is suppressed. The last of these is the technique used at RSSL and is also the method recommended by Wadds (1984). It offers the simplest approach to this type of analysis and a typical HPLC profile of 

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Rizova, V. and Stafilov, T., XAD-2 HPLC method of indentification and determination of some synthetic colourings. Anal. Lett., 28, 1305, 1995. 

Thompson, C.O. and Trenerry, V.C., Determination of synthetic colours in confectionery by micellar electrokinetic capillary chromatography, J. Chromatogr. A, 704, 195, 1995. 

Applications The potential of a variety of direct solid sampling methods for in-polymer additive analysis by GC has been reviewed and critically evaluated, in particular, static and dynamic headspace, solid-phase microextraction and thermal desorption [33]. It has been reported that many more products were identified after SPME-GC-MS than after DHS-GC-MS [35], Off-line use of an amino SPE cartridge for sample cleanup and enrichment, followed by TLC, has allowed detection of 11 synthetic colours in beverage products at sub-ppm level [36], SFE-TLC was also used for the analysis of a vitamin oil mixture [16]. 

Synthetic colours are available for almost all possible shades. Intermediate shades can be produced by blending colours. In general, synthetic colours are much more stable than natural colours to light, heat and extremes of pH. 

B I Stepanov in Recent progress in the chemistry of natural and synthetic colouring matters, Eds T S Gore et al. (New York Academic Press, 1962) 451. 

Numerous CE separations have been published for synthetic colours, sweeteners and preservatives (Frazier et al., 2000a Sadecka and Polonsky, 2000 Frazier et al., 2000b). A rapid CZE separation with diode array detection for six common synthetic food dyes in beverages, jellies and symps was described by Perez-Urquiza and Beltran (2000). Kuo et al. (1998) separated eight colours within 10 minutes using a pH 9.5 borax-NaOH buffer containing 5 mM /3-cyclodextrin. This latter method was suitable for separation of synthetic food colours in ice-cream bars and fmit soda drinks with very limited sample preparation. However the procedure was not validated for quantitative analysis. A review of natural colours and pigments analysis was made by Watanabe and Terabe (2000). Da Costa et al. (2000) reviewed the analysis of anthocyanin colours by CE and HPLC but concluded that the latter technique is more robust and applicable to complex sample types. Caramel type IV in soft drinks was identified and quantified by CE (Royle et al., 1998). 

A considerable number of foods and food products contain allowed synthetic colourants to increase the commercial value of the merchandise. Unfortunately, the illegal use of synthetic... 

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],... 

AG Fogg, AA Barros, JO Cabral. Differential-pulse adsorptive stripping voltametry of food and cosmetic synthetic colouring matters and their determination and partial identification in tablet coating and cosmetics. Analyst 111 831—835, 1986. 

Table 5.6 Artificial (synthetic) colours permitted in soft drinks to a maximum level of 100 mg/la...

As with the other additives used in soft drinks, caffeine and quinine can be, and often have been, detected using the same HPLC method used for other materials, such as in the method published by Williams (1986). This method separates most of the major additives used in soft drinks in a short time (4-5 min). Although some of the resolutions are not quite baseline, as would be expected in such a short analysis time, and not all of the synthetic colours are separated from each other, this is still a very impressive method. 

B. I. Stepanov, in Recent Progress in the Chemistry of Natural and Synthetic Colouring Matters and Related Fields ,... 

Natural and Synthetic Colouring Matters and Related Fields , ed. T. S. Gore, B. S. Joshi, S. V. Suthankar and B. D. Tilak, Academic, New York, 1962 R. Putter, Methoden Org. Chem. (Houben-Weyl), 1965,10, 631. 

Linstead RP (1935) Phthalocyanines. Part I. A new type of synthetic colouring matters. J Chem Soc 1016-1017 et seq... 

The opposites, substitutions, reversals that Synthetic Worlds traces are manifold and the themes accumulate as wilfully and refractedly as in Gravity s Rainbow. Here too chains of connection and flashes of conjunction are found between the colour wheels of eighteenth- and nineteenth-century dreamers such as Goethe and Philipp Otto Runge, the rainbow of synthetic colours and the arc of the v-2 rocket. 

Friedlieb Ferdinand Runge was a chemist attuned to the aesthetic side of chemistry. As chemist proper, he produced the first synthetic colour in 1833. As experimenter, his Romantically accented philosophy of nature and his Goethean morphological approach allowed him to generate glorious... 

A rainbow of synthetic colours appeared. Chemists had cracked the chemical structure of colour. Synthetic alizarin allowed thousands of new colours to be produced. Even the legendary Tyrian purple squeezed from the juice of molluscs was duplicated in German laboratories. Nature gave birth to a parallel world, a second nature - artificial colours, then later textiles, substances, any manner of materials. For Engels, the extraction of alizarin and its synthetic reproduction changed everything ... 

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