A 7Li nuclear magnetic resonance study of solutions of lithium and ammonium ions with nitrilotriacetic acid

Abstract

The possibility has been explored of using the ⁷Li resonance to measure complex formation in solution between nitrilotriacetic acid (NTA) and lithium ions. It has been found that, as the proportions of lithium and NTA are varied, the ⁷Li chemical shift changes in such a way as to suggest the formation of a complex Li(NTA)₂^5–. The results are explained on the basis of equilibria involving this complex, the already known LiNTA^2–, Li⁺aq., and NTA^3–. The addition of other ions also affects the ⁷Li chemical shift, and the formation of complexes between these ions and NTA is inferred. The results for the ammonium ion can be explained by the formation of complexes NH₄(NTA)^2– and (NH₄)₂NTA^–.