Magnetometric Titration: a New Method of Chemical Analysis

Abstract

IT is well known that the addition of paramagnetic solutes to water brings about a marked reduction in the nuclear spin-lattice relaxation time of solvent protons1, the inverse of the relaxation time being linearly related to solute concentration according to the equation: where T 1 and T 0 are spin-lattice relaxation times in the presence and absence of added solute, respectively; α is a proportionality constant; μN is a parameter expressing the effectiveness of a particular solute in this phenomenon, sometimes called the ‘effective’ paramagnetic moment of the solute; C is the concentration of the solute. In the case of solutions of paramagnetic complex ions, the magnitude of the effect (that is, the value of μN) depends on the nature of the co-ordinated groups2. We find that the phenomenon enables the replacement of one ligand by another in solution to be followed with sufficient precision to form the basis for a method of determining the concentration of metal ions, and it is now suggested that this method of analysis should be widely applicable in cases where the addition of a complexing agent to the solution of a paramagnetic ion in solution causes the formation of a new complex ion of different μN and of high stability in solution. The analyses can conveniently be carried out by use of a low-resolution nuclear magnetic-resonance spectrometer.