Which dye is used in calcium dye-binding method besides CPC?

• A. Arsenazo III
• B. Murexide
• C. Eriochrome Black T
• D. Alizarin Red S

Answer: (A)

Calcium dye-binding methods quantify calcium by forming a colored complex between calcium ions and a dye, and the color intensity reflects the calcium concentration. Besides Cresolphthalein Complexone (CPC), Arsenazo III is the dye commonly used to form a stable Ca2+-Arsenazo III complex. In this method, calcium ions bind the Arsenazo III dye in a buffered solution, producing a magenta-colored complex whose intensity is measured spectrophotometrically to determine calcium levels. This makes Arsenazo III a well-established alternative to CPC for routine calcium assays in serum or plasma. Other dyes exist in different protocols, but Arsenazo III is the standard partner with CPC in the dye-binding approach for calcium.