Determination of Synthetic Colorants in Foodstuffs
Department of Chemistry and Biochemistry, Mendel University of Agriculture and Forestry, Brno
Synthetic dyes can be determined in solid food, in non-alcoholic drinks and their concentrates by several separation and spectrometric methods (LC, CE, UV/VIS). All the methods give similar results for most samples. Direct UV-VIS spectrophotometry gives very good results if a single colorant or a mixture of colorants of different absorption spectra is present or if the colorants can be completely separated by solid-phase extraction. If this is not the case, the simple multicomponent analysis leads to deviations up to 10 - 15%. More complicated programs for multicompoment analysis (PLS, nonlinear regression) have to be used in such cases and also when other constituents (sugars, phenolics, etc.) are present at high concentrations.
Capillary electrophoresis (CE) is the method of choice for determination of anionic synthetic dyes in biological materials and foodstuffs since it can separate the dyes in a single analysis within a short run time, gives very precise and accurate results, reduces sample consumption and, under optimum conditions, is not time-consuming. The necessity of sample pretreatment is a certain disadvantage of CE in comparison with HPLC. CA also enables separation of synthetic colorants from hydrophobic natural pigments. For the identification and determination of the latter, LC methods are well established. Their sensitivity is usually by more than an order of magnitude higher, their separation efficiency is mostly sufficient, and sample pretreatment is simpler.
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