Determination of the relative amounts of free and complexed manganese ions in aqueous solution by nuclear magnetic resonance

• Published in: Analytical chemistry (Washington) Vol. 63; no. 24; pp. 2919 - 2924
• Main Authors: Kellar, Kenneth E, Foster, Natalie
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.12.1991
• Subjects: Analytical chemistry; Chemistry; Exact sciences and technology; Magnetic Resonance Spectroscopy; Manganese - analysis; Solutions; Spectrometric and optical methods; Chemical analysis; Spin lattice relaxation; Organic ligand; Manganese III Complexes; Metalloporphyrin; NMR spectrometry; Aqueous solution; Speciation; Manganese II Ions
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac00024a022

The ratio of the transverse relaxation rate to the longitudinal relaxation rate of water protons (T1/T2) at 90 MHz can be used to determine the relative amounts of free Mn2+ ions (the hexaquo ion) and chelated manganese ions when both species are present in the same aqueous solution. This technique is demonstrated for simple aqueous solutions containing known concentrations of both the free Mn2+ ion and a manganese(III) porphyrin. The accuracy of the method is found to be +/- 7.3% for the solutions considered in this report. The determinations of the relative amounts of the free Mn2+ ion and the manganese(III) porphyrin by this T1/T2 method are shown to agree well with those determined by nuclear magnetic resonance dispersion profiles. The theoretical basis of this ratio method as well as the scope and limitations in its application to aqueous solutions containing both free Mn2+ ions and chelated manganese species other than manganese(III) porphyrins are also discussed. This work demonstrates a unique use of NMR as a means for the quantitative analysis of manganese in which the effects of the metal ion on the solvent, and not the metal itself, are observed.