Synthetic colours: analysis

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]. 

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). 

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],... 

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. 

A different system has been introduced by Index Instruments [2]. This modular analysis system (MAS) provides the analysis of up to four different parameters refractive index, density, colour and optical rotation. A wide range of viscosities can be handled. The analysis, wash and drying times can be selected by computer control so that crosscontamination can be reduced to undetectable levels. Samples are only in contact with inert materials such as glass, synthetic sapphire, PTFE and 316 stainless steel. 

The discussion above has addressed the assessment of a product s colour or perceived colour in basic terms. In the next two sections, methods to determine which coloured compounds are present in a product will be addressed. For the purpose of this chapter, the section on synthetic dyes will cover the analysis of the water-soluble dyes, or so-called coal tar dyes, and the section on natural pigments will cover the anthocyanin pigments, such as grape skin extracts, and the carotenoid-based materials, even if they are of synthetic origin. 

Wadds, G. (1984) Analysis of synthetic food colours, in Developments in Food Colours—2 (ed. J. Walford), Elsevier Applied Science, London, pp. 23-74. 

So what should we make of all this The upshot of all this analysis would appear to be that modern hair dyes present no risk of causing cancer either among those who apply them or those on whose hair they are applied. If you are still not convinced that synthetic chemical dyes are safe, and yet you want to change the colour of your hair or hide any grey then you must perforce turn to the dyes of old - see box - but even some of these should come with test patches and a warning. 

Fibres are the single strands of a polymer, whether natural or synthetic, that are spun together to produce yarns used in the manufacture of fabric to produce garments and upholstery (as well as other applications). These fibres or yarns will have been treated before they are used to produce the fabric, and part of this treatment will involve the application of colour or dyeing in order to make the garments and fabrics more appealing to the consumer. Due to their commonality, it is not surprising that fibres are frequently submitted to the forensic laboratory for analysis. 

Most of the techniques employed in fibre analysis are nondestructive tests to determine whether the fibre is natural (obtained from animal, plant, or mineral) or synthetic (wholly manufactured from chemicals or regenerated from natural fibres) and the fibre type (e.g., determining if the fibre is wool, cotton, nylon, polyester, etc.). Whether any chemical treatments have been carried out (such as bleaching or the use of delustrants) is noted and the colour is also determined. Many of the techniques commonly used in these analyses include low- and high-power microscopes, Fourier transform infrared (FTIR) microscopy, polarising Ught microscopy, fluorescence microscopy, and microspectrophotometry (MSP). 

Jaworska, M. Szulinska, Z. Wilk, M. Anuszewska, E. Separation of synthetic food colourants in the mixed micellar system. Appheation to pharmaceutical analysis. J. Chromatogr., A 2005,1081,42-47. 

Before the advent of infra-red analysis, natural rubber (and gutta percha) was identified by the Weber test which involved bromination. The rubber was reacted with bromine to form a dibromide which was then treated with a solution of phenol in carbon tetrachloride. A violet colouration of the residue developed after gentle boiling of the mixture. (This test also gives positive results for synthetic polyisoprenes and butyl rubber.)... 

Humbach 0., Fabian H., Grzesik U., Haken U., Heitmann W Analysis of OH absorption bands in synthetic silica. J. Non-Cryst. Solids 1996 203 19-26 Hunt R.W.G. Measuring Colour, 3rd ed. England Fountain Press, 1998 Her R.K. The Chemistry of Silica. New York John Wiley Sons, 1979... 

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