Quantitative electron paramagnetic resonance and spectrophotometric determination of the free radical 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy

The first quantitative estimation of the stable free radical 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (TEMPOL) simultaneously performed by electron paramagnetic resonance (EPR) and visible spectrophotometric titration is reported. The obtained molar absorptivity of TEMPOL 13.2 +/- 0.11(-1) m(-1) cm(-1) at 22 900 cm(-1) may be used as the future criterium about the purity of the EPR active substance. The studied compound may be considered as the second (after 1,1-diphenyl-2-pikrilhydrazil) material calibrated as the primary standard for quantitative EPR spectrometry. (C) 2000 Elsevier Science B.V. All rights reserved.