Synthetic colorants separation techniques

Recently a new method was developed for the complete liquid chromatographic separation and diode array detection of standard mixtures of the 14 most frequently used synthetic colorants. Protocols for RP-HPLC - " and IP-HPLC techniques have been extensively described and the techniques were compared with micellar electrokinetic capillary chromatography, - which has been shown to be suitable for the analysis of synthetic colorants. 

All these methods give similar results but their sensitivities and resolutions are different. For example, UV-Vis spectrophotometry gives good results if a single colorant or mixture of colorants (with different absorption spectra) were previously separated by SPE, ion pair formation, and a good previous extraction. Due to their added-value capability, HPLC and CE became the ideal techniques for the analysis of multicomponent mixtures of natural and synthetic colorants found in drinks. To make correct evaluations in complex dye mixtures, a chemometric multicomponent analysis (PLS, nonlinear regression) is necessary to discriminate colorant contributions from other food constituents (sugars, phenolics, etc.). 

The purpose of this section is to provide a review of HPLC methods available for the determination of synthetic colors in foods, including sample preparation, separation techniques, and detection systems. 

Several hundred dyes are known, and this diversity has always posed a problem of identity for the analysis, for many dyes have similar characteristics and some occur as a mixture (158). Among the different techniques available for the analysis of food colors, HPLC can replace many of the traditional techniques, providing rapid results that are much more specific for the determination of colorants (131,142). The technique has been shown to have great potential for synthetic food color analysis in terms of simultaneous separation, qualitative identification, and quantitation (159). 

HPLC has been considered a powerful technique for the analysis of synthetic food color, for the detection of impurities in single dyes and also for the separation of a mixture of dyes (153). Re-versed-phase ion-pair chromatography has been found particularly useful for the separation and detection of a large number of food colors (159). 

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. 

Color Plate 3 Dual-channel imaging technique. Bacterial cells were grown in synthetic medium without nitrate to an optical density at 500 nm (OD500) of 0.5. The proteins were labeled with [ S]-L-methionine 20 min after transfer to anaerobic conditions. Protein extracts were separated on 2D gels. The resulting images from the protein synthesis... 

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