Synthetic colorants detection systems

The combined use of a continuous flow system and a spectrophotometer for sample screening to discriminate between synthetic and natural colorants is also available. With a very simple flow system on a column packed with natural materials, one can discriminate natural and synthetic colorants. The natural (not retained) ones can be determined in the first step and the synthetic (retained) ones in the second step after their elution. For yellow, red, green, blue, and brown, natural or synthetic colorants were chosen as models. The specific maximum wavelength for each color (400,530, and 610 mn, respectively) was selected by a diode array system. A complete discrimination of natural and synthetic colorants was obtained for concentrations of natural colorants (in the absence of synthetic ones) up to 2000 (yellow), 2000 (red), and 10,000 (brown) times that of the detection limits (DLs) of synthetic additives. This method was applied to screen fruit drinks and candies. ... 

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. 

A number of substrates and complex auxiliary and indicator systems are used in spectrophotometric methods. In the Ortho Diagnostics Vitros spectrophotometric reaction rate LPS slide method, tlie (synthetic) substrate is 1-oleoyl-2,3-diacetyIglyceroI and the emulsifier dodecylbenzene sulfonate. LPS activity is measured by a complex auxiliary and indicator enzyme system to produce a colored dye detectable at 540 nm. However, the substrate is likely to be more specific for intestinal than pancreatic LPS and may be subject to interference by postheparin fipase and pancreatic car-boxylesterase. An upper reference limit of 200 U/L at 30 °C has been reported. 

SPA technology requires only pipetting steps and there is no need to use scintillation cocktails or to perform a separation, and thus it is ideally suited for automation by robotic liquid handling systems. However, as a consequence of the nonseparation SPA method and due to the screening of colored synthetic or natural compounds, it is essential that the detection instrument accurately assesses the level of color quenching and corrects the observed count rate (cpm) to the true activity (dpm) [49]. 

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