Potassium ferricyanide(II) 1%, also known as yellow blood liquor salt, is an in vitro diagnostic agent mainly used for the identification and quantification of iron in biological samples. By forming a deep blue complex, also known as Prussian blue, when reacting with iron ions, this solution allows reliable and sensitive detection of iron.

In clinical chemistry and pathology, it is widely used in the diagnosis and monitoring of disorders of iron metabolism. For example, it can be used to determine serum iron or for histological staining of iron stores in tissue samples.

The chemical reaction that enables detection is based on the ability of iron(III) ions to react with potassium ferricyanide(II) to form the characteristic Prussian Blue complex. This process is quantitative and therefore provides an accurate method for determining the iron content in a sample.