Colours permitted

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

Food colours are broadly divided into two classes natural and artificial. In the United States, these are listed as either exempt from certification or certified . The natural colours are botanical extracts, with the exception of carmine (a red colour), which should perhaps be termed an entomological extract as it is obtained from the insect Dactilopius coccus, sometimes termed the cochineal beetle, which breeds and feeds on particular cacti indigenous to Central and South America. Table 5.6 lists artificial colours permitted in soft drinks under EU legislation. 

According to the Directive, the term caramel relates to products of a more or less intense brown colour, which are intended for colouring. It does not correspond to the sugary aromatic product obtained from heating sugars and which is used for flavouring food (e.g., confectionery, pastry, and alcoholic drinks). Caramel is the only colour permitted in malt bread, vinegar, and alcoholic drinks, such as beer, whisky, and liqueurs. 

Fast Green FCF and Quinoline Yellow are colours permitted to be used in foods and cosmetics and have the structures shown here. Quinoline Yellow is a mixture of isomeric sulfonic acids in the two rings shown. 

The colour reactions with the enzyme peroxidase and HjO permit all the above amines to be distinguished from one another in very dilute solution (P- 523)-... 

The p-phenetidine is usually coloured and the procedure given permits a preliminary treatment with decolourising carbon, thus leading to an almo.st colourless phenacetin directly. 

As the result of the performed investigations was offered to make direct photometric determination of Nd microgram quantities in the presence of 500-fold and 1100-fold quantities of Mo and Pb correspondingly. The rare earth determination procedure involves sample dissolution in HCI, molybdenum reduction to Mo (V) by hydrazine and lead and Mo (V) masking by EDTA. The maximal colour development of Nd-arsenazo III complex was obtained at pH 2,7-2,8. The optimal condition of Nd determination that was established permit to estimate Nd without separation in solution after sample decomposition. Relative standard deviations at determination of 5-20 p.g of Nd from 0,1 g PbMoO are 0,1-0,03. The received data allow to use the offered procedure for solving of wide circle of analytical problems. 

New stationary phases for specific purposes in chromatographic separation are being continually proposed. Charge transfer adsorption chromatography makes use of a stationary phase which contains immobilised aromatic compounds and permits the separation of aromatic compounds by virtue of the ability to form charge transfer complexes (sometimes coloured) with the stationary phase. The separation is caused by the differences in stability of these complexes (Porath and Dahlgren-Caldwell J Chromatogr 133 180 1977). 

Stability of the colour. The colour produced should be sufficiently stable to permit an accurate reading to be taken. This applies also to those reactions in which colours tend to reach a maximum after a time the period of maximum colour must be long enough for precise measurements to be made. In this connection the influence of other substances and of experimental conditions (temperature, pH, stability in air, etc.) must be known. 

The reflected light from polished surfaces permits ready distinction between many opaque minerals on the basis of brightness, colour, and anisotropy. This feature is very important in the study of ore minerals and host rocks. Transparent minerals (especially in rocks) are commonly studied by transmitted light. In this case, polarized light is passed through thin sections or through fragments mounted in oil. 

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