Dye Elution from Aluminum Lakes of Synthetic Food Color (I)

Tartrazine Lakes from Commercial Origins

Abstract

Dye elution in NaCl aqueous solution was examined for Tartrazine aluminum lakes from various commercial origins. The concentration of eluted dye anion [D]_s was measured as a function of the lake/solution ratio W_p and time, which gave a set of elution curves marked by the following features : (1) [D]_s increased keeping up with W_p and (2) [D]_s depended on time in two different ways by lakes of different origins : for one way, [D]_s increased consistently with elapse of time, and for the other, [D]_s increased in the initial stage and then turned to decrease giving a maximum. This fact indicated that contradictory results might be obtained in grading the anti-eluting strength of lakes, based on the usually-adopted method when [D]_s is measured at a fixed condition with respect to W_p and time, if the condition is changed to any different level.
The observed dye elution features were interpreted by a mechanism where the anion exchange reaction between Cl- ions in the NaCl solution and dye anions in the lake was supposed to proceed in the peripheral reacting zone of lake particle with the depth of 40 A or so, while the central core with the diameter of 1500 A or so remained unaffected. Linear relationships demanded by the mechanism between 1/[D]_s and 1/W_p introduced two kinds of values that should be related to the distribution coefficient K of the dye anion and the weight fraction η of the peripheral reacting zone for the whole particle, respectively. These values proposed a method to compare the anti-eluting strength of aluminum lakes.