Identification and quantification of radical species by 31P NMR-based spin trapping — A case study: NH4OH/H2O2-based hair bleaching

• 31P NMR-based spin trapping allows quantifying radical species generated in of ammonium salts / hydrogen peroxide mixtures.
• With suitable modifications, this method allows the study of bleaching systems of human hair.
• Different bleaching systems differ in nature and amounts of the radical species generated upon reaction with human hair.
• Presence and abundance of different radical species can be correlated to the nature of the bleaching systems.
• The main species involved in the process were superoxide and amino radicals.

The 31P NMR-spectroscopy-based spin trap technique involving 5-diisopropoxy-phosphoryl-5-methyl-1-pyrroline-N-oxide (DIPPMPO) was used to achieve quantitative analyses of the radical species that are generated in different bleaching solutions. These solutions comprised a mixture of an ammonium salt and hydrogen peroxide. This spin trap-based approach was also applied, with modifications, to the study of bleaching systems of human hair. The obtained results clearly revealed the subtle differences in both the nature and the amounts of the radical species generated in different bleaching solutions, and when allowed to react on hair samples. Generally, the main species involved in the oxidation processes were superoxide and amino radicals. Their amounts, however, showed a significant variation upon the kind of bleaching system and nature of the hair, i.e., virgin or dyed hair.