Free radical quantification in chemical systems: Challenges and future perspectives

The importance of free radicals in several chemical and biological systems has been extensively documented in the literature. Free radical detection is possible through techniques such as electron spin resonance (ESR), chemically induced dynamic nuclear polarization (CIDNP), and biochemiluminescence. Herein, we provide a comprehensive review of free radical detection, with an emphasis on free radical quantification. The ability to control free radical reactions of various matrices necessitates measuring free radical concentration, which can be obtained by quantifying free radicals. In the current work, we provide a review of various methods and procedures employed for free radical quantification in chemical systems. Procedures were discussed in detail and then grouped based on the instrument used, the operating conditions, and the methodology employed to convert the ESR signal obtained to free radical spins per unit mass of sample. We also provide a comparison with free radical quantification in biological systems. It was found that there is a notable dearth of work focused on quantification in chemical systems despite its potential to enhance control over free radicals. In the last part of this manuscript, we provide a summary and suggested methodology for free radical quantification in chemical systems using ESR focusing on factors affecting quantification.