Ponceau S, Acid Red 112, or C.I. 27195 is a sodium salt of a diazo dye that may be used to prepare a stain for rapid reversible detection of protein bands on nitrocellulose or PVDF membranes (Western blotting), as well as on cellulose acetate membranes. A Ponceau S stain is useful because it does not appear to have a deleterious effect on the sequencing of blotted polypeptides and is therefore one method of choice for locating polypeptides on Western blots for blot-sequencing. It is also easily reversed with water washes, facilitating subsequent immunological detection. The stain can be completely removed from the protein bands by continued washing. Common stain formulations include 0.1% (w/v) Ponceau S in 5% acetic acid or 2% (w/v) Ponceau S in 30% TCA and 30% sulfosalicylic acid.
Its CAS number is [] and its SMILES structure is OC1=C(N=NC3=C C=C(N=NC4=CC=C (S(=O)(O)=O)C=C4) C=C3S(=O)(O)=O) C2=C(C=C(S(=O) (O)=O)C=C2)C=C1 S(=O)(O)=O.