Appropriate amounts of powder of each color (except E102 and metanil yellow) were dissolved in methanol/water (1:1 v/v) to give a concentration of 1000 mg l1. Tartrazine and metanil yellow were dissolved inwater at the same concentration.
solution. Calibration curves of the four groups ranged from 1 to
100 mg l1. The solvent for all dilutions was methanolewater
(1:1 v/v).