Rapid and simultaneous relaxometric methods to study paramagnetic ion complexes in solution: An alternative to spectrophotometry

• Simple, rapid and simultaneous relaxometric method to study complexes containing paramagnetic cations in solution is shown
• The method has several advantages over spectrophotometry
• The method can be used to study colorless not accessible by spectrophotometry
• The analysis is performed in low-cost bench top time-domain NMR spectrometer

T1 and T2 relaxation times, measured with rapid and simultaneous continuous wave free precession (CWFP) and Carr–Purcell-continuous wave free precession (CP-CWFP) pulse sequences were used to study complexes of EDTA with paramagnetic ions in solution. The relaxation times of Cu(II)-EDTA and [CuEDTA.NH3]− 2 complexes, from pH 1 to 13, measured in a 0.47 T time-domain nuclear magnetic resonance (TD-NMR) spectrometer show good agreement with the absorbance at approximately 730 nm. These methods were also used to study colorless complexes containing paramagnetic ions, not accessible by electronic spectroscopy, such as Mn(II)-EDTA. Therefore, these sequences can be used in any bench top TD-NMR spectrometers as faster alternative to spectrophotometry in analytical routine analyses.