The Amplite® Colorimetric Phenolic Compounds Assay Kit is a highly sensitive and specific assay for quantifying total phenolic content in diverse biological samples. The assay is based on the reaction between phenolic compounds and diazonium salts under alkaline conditions, forming a stable diazo chromophore that can be quantified by absorbance at 480 nm. Unlike the Folin-Ciocalteu method, this assay minimizes interference from non-phenolic reducing agents such as sulfites, reducing sugars, and ascorbic acid, ensuring greater specificity for phenolic compounds. With a detection limit of 0.02 mM catechin equivalents (CEs), the assay is compatible with high-throughput workflows and is validated for applications involving complex matrices such as fruits, vegetables, beverages (e.g., tea, wine, coffee), processed food products, plant extracts, and herbal or nutraceutical formulations. Phenolic compounds are a diverse group of phytochemicals widely distributed in dietary and medicinal plants, including fruits, vegetables, cereals, and beverages such as tea, coffee, and wine. These compounds, encompassing phenolic acids, flavonoids, stilbenoids, lignans, and polyphenols, play essential roles in plants, such as UV protection, herbivore deterrence, and developmental signaling. In humans, their potent antioxidant properties have been linked to reduced risks of cardiovascular diseases, cancer, and neurodegenerative disorders. Additionally, their antimicrobial, anti-inflammatory, and immunomodulatory effects underscore their significance in both biomedical research and dietary science.