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. Author manuscript; available in PMC: 2011 Feb 5.
Published in final edited form as: J Chromatogr A. 2009 Oct 2;1217(6):902–924. doi: 10.1016/j.chroma.2009.09.073

Fig. 20.

Fig. 20

Structures of stable free radicals. 21 2,2,6,6-tetramethyl-1-piperidyloxy (TEMPO); 22 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (TPPA); 23 3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-1-oxy (3-carboxy-PROXYL); 24 4-carboxy-2,2,6,6-etramethylpiperidinyl-1-oxy (4-carboxy-TEMPO).