²³Na NMR relaxation rate studies in hydrocolloid-NaCl solutions as influenced by NaCl concentration and pH

²³Na NMR longitudinal (R₁) and transverse (R₂) relaxation rates were measured for 0.5 g/L aqueous solutions of sodium carboxymethyl-cellulose (CMC) and methylcellulose (MC) as a function of added NaCl (0 to 800 mg/100 mL) and pH (2 to 13). In the case of CMC. R₁ and R₂ decreased rapidly as the concentration of added NaCl increased. Whereas in the case of MC, after a small initial decrease, R₁ and R₂ were relatively constant with increasing added NaCl. This difference in relaxation rates was attributed to the difference in the chemical nature of the two hydrocolloids. R₁ and R₂ increased as pH increased from 2 to 7 for CMC at 0 and 50 mg added NaCl/100 mL. This increase in R₁ and R₂ is attributed to the deprotonization of the carboxyl group at approximately pH 4.5.