A Demonstration of Principal Component Analysis for EPR Spectroscopy: Identifying Pure Component Spectra from Complex Spectra

The application of principal component analysis (PCA) with self-modeling (SM) is extended to electron paramagnetic resonance (EPR) spectroscopy. Our approach develops a novel constraint in the SM procedure. This constraint relies on the mirror symmetry around the EPR peak position, a condition that is well satisfied by most paramagnetic compounds at the usual EPR measurement frequencies (9−10 GHz, the X-band). Examples considered are two- and three-component systems consisting of aqueous solutions of paramagnetic ions that exhibit distinct but overlapping spectra: Cu 2+ (single peak), Mn 2+ (sextet), and VO 2+ (octet). The results show that the PCA technique is capable of reproducing the correct number of components and reconstructing spectra in good agreement with control measurements. Other spectroscopy areas to which the symmetric peak constraint should be applicable include NMR, NQR, and ICR.