Use of UV-Visible absorption measurements for Pt-Co color analysis and yellowness index calculations

Pt-Co, Hazen, and APHA color are three different terms referring to the same color analysis procedure often used to assess the yellowness of water samples. In this analysis a mixture of cobalt chloride and potassium hexachloroplatinate(IV) is prepared and subsequently diluted by varying amounts to form an array of yellow to almost colorless standards, as described in ASTM D1209 and ISO 6271:2015.