following CR11 treatment, respectively. Divalent ions such as Cu2+and Zn2+ are known to bind iminodiacetic acid. However, Mg and Ca concentrations were maintained at approximately 33 and 11 mg/100 mL, respectively, following CR11 treatment, but were decreased to half of those in untreated fish sauce, potentially reflecting low binding constants of these metals. Because Cu, Zn,Mg, and Ca concentrations are low in untreated fish sauce, these decreases may not have a significant impact on the quality of fish sauce, although their adsorption by CR11 may competitively inhibit Cd removal. Na and K concentrations in fish sauce were 7.5 ± 0.01 g/100 mL and 103 ± 4 mg/100 mL, respectively. Because alkaline metals do not bind iminodiacetic acid with high affinity,Na and K concentrations were not significantly altered after resin
treatments. Na is predominantly present as NaCl in fish sauce and is an important preservative that inhibits microbial contamination. Thus, maintenance of Na concentrations is critical for the quality of fish sauce.