Free radicals generated by exposing amino acids to Ti-H₂O₂ flow mixing system were identified by electron spin resonance spectroscopy. Hydrogen atom abstraction by the reactive primary radical, having electrophilic character, was found to occur at the carbon atom furthest from the guanidium, carboxyl and protonated amino group, and sulfur atom. The main radical species from DL-leucine, DL-methionine and L (+) arginine were assigned to be CH₂CH (CH₃) CH₂CH (NH₃^+)COO^-, CH₃SCH₂CHCH(NH₃^+)COO^- and NH=C(NH₂)NHCH₂CHCH₂CH(NH₃^+) COO^- respectively. The splitting for the hydroxyl hydrogen was also clearly observed in the system for DL-serine free radical, CH (OH) CH (NH₃^+) COO^-. Generally, HCl appeared to interfere with the free radical production for most of the amino acids investigated except L-cysteine and DL-methionine in contrast with H₂SO, which enhances most signals but not with the latter.