Fig. 1. (A) Representative room temperature EPR spectra of 100 µM Mn_T as birnessite (0.45 m² L^-1) reacted with catechol (5 x 10^-3 M) depicting the characteristic six-line spectra of the Mn(II) product. H₀ and H₁ indicate the peak and valley used to quantify Mn(II) concentrations. (B) Intercalibration standard curve relating EPR signal intensity at the 0.3435 T (H₀) peak to flame AAS Mn(II) concentration