4-Sulfophenyl diazonium salt, a new, precise and selective alternative to the Folin-Ciocalteu method for the quantification of phenolic compounds.

Quantifying total phenolic compounds (TPC) is essential in food and agricultural sciences. Although the Folin-Ciocalteu assay is versatile and widely reliable, non-phenolic reducing agents can interfere significantly in complex matrices. Diazonium salts, highly selective for aromatic electrophilic substitution, react exclusively with phenol derivatives and anilines. This study investigated 4-sulfophenyl diazonium chloride (4SPD) for TPC quantification. 4SPD was synthesized by diazotizing sulfanilic acid with sodium nitrite and hydrochloric acid, then characterized via 1H NMR, FT-IR spectroscopy and LC-MS. A calibration curve was constructed using gallic acid (40-400 mg L-1) with a quantification limit of 3 mg L-1. Operating signal was achieved at 50% methanol in water. The method demonstrated excellent precision, accuracy, and robustness with no significant deviation from 100% recovery. Validated across diverse simple and complex matrices with R2 = 0.933 correlation against HPLC-DAD, 4SPD proved to be a selective, precise, and robust method for TPC quantification.