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
Wp and time, which gave a set of elution curves marked by the following features : (1) [
D]
s increased keeping up with
Wp 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
Wp 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/
Wp 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.
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