Behavior of Dissociated Salts in Aqueous Solution: Insights From T₂ Relaxation Time and Signal Intensity Using a...

This study explores the influence of NaCl, KCl, CaCl₂, and MgCl₂, salts commonly used in the food industry, on aqueous solutions using transverse (T₂) relaxometry in low- field nuclear magnetic resonance (LF-NMR) at a salt-to-water ratio ranging from 0 to 0.1079 mol/mol. The results demonstrate that T₂ relaxation times are significantly affected by the chemical nature and concentration of the ions, with divalent salts exhibiting distinct behavior compared to monovalent salts. Notably, the kosmotropic (structure-making) and chaotropic (structure-breaking) properties of the salts were found to influence relaxation times. Mg²⁺ exhibited the most pronounced effect (low relaxation time) due to its high charge density and strong hydration ability, followed by Ca²⁺, Na⁺, and K⁺. Relaxation times decreased with increasing salt concentration for MgCl₂, CaCl_2, and NaCl (from 3080 ms at 0% to 504, 1671, and 2796 ms at 0.1079 mol/mol, respectively), whereas the chaotropic KCl solution had extended relaxation times (3884 ms at 0.0771 mol/mol). A novel finding of this study is the exponential decay of peak area in salt solutions, as evidenced by experimental data. The alteration in the structural arrangement of water and the synergistic movement of cations or anions in higher-mass salt solutions are hypothesized to underlie the observed behavior, although the exact reason requires further study. Electrical conductivity (EC), water activity, and the enthalpy of solution upon salt incorporation provide further insights into the behavior of salt solutions. This research advances the understanding of how ionic solutes modulate water dynamics, affecting both relaxation time and the total peak area.