SODIUM-23 NUCLEAR MAGNETIC RESONANCE STUDIES OF SODIUM AMINOCARBOXYLIC ACID COMPLEXES

Nuclear magnetic resonance (nmr) relaxation time measurements of23Na have been used to study sodium ion complexes with ethylenedinitrilotetraacetic acid (EDTA), Nʹ-(2-hydroxyethyl)ethylenediamine-N,N,Nʹ-tri-acetic acid (HEEDTA), and nitrilotriacetic acid (NTA) in aqueous solution. The pH dependence of the23Na spin-lattice relaxation time (T1) demonstrates a chelate effect and identifies the important chelating groups. Analysis of 23Na spin-lattice relaxation times as a function of total sodium ion and total ligand concentrations permits measurement of the complex formation constant (K1) and the relaxation time of the bound sodium (71B). The results are (at 25°, ionic strength variable between 0.7 and 1.0): for HEEDTA, Kf = 8.7 ± 0.9 M-1, [formula-omitted] = 610 ±30 sec-1; for NTA, Kt = 9.6 ± 1.5 M-1 [formula-omitted] = 525 ± 40 sec-1 (95% confidence limits given). In addition it is shown that histidine is ineffective in complexing sodium, contrary to what has been previously reported. © 1969, American Chemical Society. All rights reserved.