Polyanions and their complexes. Binding affinities of inorganic ions to carrageenans and carboxymethylcellulose

Abstract

The effect of inorganic ions on the interaction between Methylene Blue and κ and λ carrageenan fractions and carboxymethylcellulose (CMC) has been investigated using visible absorption spectroscopy. The concentration of ions required to remove completely Methylene Blue (MB) from the MB–polyanion complex i.e. the limiting salt concentration, has been determined and found to decrease in the order Li⁺ > Na⁺ > K⁺ > Cs⁺, and Mg²⁺ > Ca²⁺ > Sr²⁺ for carrageenans and K⁺ > Na⁺ and Mg²⁺ > Ca²⁺ > Sr²⁺ for CMC. Comparing ions of the same valency, the strength of binding is greatest for the smallest hydrated ion, and decreases in proportion to the hydrated ion size, except for the alkali ions with CMC, when the opposite is the case.