Description General description Ponceau S is the sodium salt of a diazo dye. It is used to make a stain for rapid reversible staining of protein bands on nitrocellulose or PVDF membranes (Western blots) and also for staining protein on cellulose acetate membranes. The stain is reversed with water washes and aids in subsequent immunological detection.[4] The following are two common stain formulations: 0.1% Ponceau S (w/v) in 5% acetic acid 2% Ponceau S (w/v) in 30% TCA, 30% sulfosalicylic acid Application Ponceau S has been used for membrane staining (Western blotting.[1][2][3] Packaging 10, 50, 100 g in glass bottle