Lowry’s reagent is used in the Lowry protein assay to measure protein concentration. It contains copper ions and alkaline tartrate, which react with proteins to form a complex. After this reaction, the Folin–Ciocalteu phenol reagent is added, producing a color change. The intensity of the resulting color, typically measured at 750 nm, is directly proportional to the protein concentration. The Lowry method is highly sensitive and widely used for accurate protein quantification.