Formula: C₂₀H₁₅N₄NaO₆S (2-carboxy-2'-hydroxy-5'-sulfoformazylbenzene) CAS: 62625-22-3 EC No.: 263-571-8 M (Molar Mass): 462.41 g/mol D (Density): Not applicable mp (Melting Point): >250°C (decomposes) bp (Boiling Point): Not applicable Optical Rotation: Not applicable

Assay (Spectrophotometric): ≥ 98.0 % Appearance: Orange to reddish-brown powder Solubility: Soluble in water and alkaline solutions λmax (in water, pH 9): ~620 nm (free ligand), ~620 nm (Zn complex) Zinc Complex: Forms blue complex with Zn²⁺ at pH 9.0 (ε ~ 2.0×10⁴ L·mol⁻¹·cm⁻¹) Interference: Copper and mercury also form colored complexes Loss on Drying: ≤ 5.0 % Residue on Ignition: 8.0 – 12.0 %