Abstract

The change in absorbance of a solution may be used to follow the change in concentration of a radiation-absorbing constituent during a titration. The absorbance is directly proportional to the concentration of the absorbing constituent. This method might be useful to determine bromination reaction in colorful crackers, which are favourite food of children and adults in our country, Indonesia. In this work, we determined red and yellow dyes in unregistered crackers sold at Jatinangor, West Java, Indonesia. The dyes were isolated by extraction using a mixture of 2% of ammonia in 70% ethanol continued by preparative thin layer chromatography on GF254 silica gel plate and were separated and analyzed by using FTIR-8400 Shimadzu infrared spectrophotometer. Bromination reaction was measured by using photometric titration method.  Thin layer chromatograms showed that the dyes were not either rhodamine B or tartrazine (Rf of the red and yellow dyes were 0.714 and 0.652, respectively, while those of rhodamine B and tartrazine were 0.591 and 0.673). Infrared spectroscopy showed characteristic peaks of the red dye at 3390.6 cm^-1(O-H stretch), 2927.7 cm^-1(C-H stretch of alkyl), 1404.1 cm^-1 (O-H bend), 1616.2 cm^-1(C=C stretch), and 1315 cm^-1 (C-O stretch). The peaks of yellow dye occured at 3413.8 cm^-1, (O-H stretch), 3213.2 cm^-1 (C-H stretch of alkene), 2927.7 cm^-1(C-H stretch of alkyl), 1400.2 cm^-1(O-H bend), 1624.0 cm^-1 (C=C stretch). Visible spectroscopy showed maximum wavelengths at 551 nm (red dye) and 432 nm (yellow dye). Photometric titration to determine bromination reaction in the dyes showed a decreasing in absorbance due to the conversion of colored analytes to colorless products. This fact indicated that bromination reaction was occured in the red and yellow dyes molecules via electrophilic addition reaction on its double bond.

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