Loba | Eriochrome Black T | 1787-61-7 | Solochrome Black T | Sodium 4-[(1-hydroxynaphthalen-2-yl-hydrazinylidene]-7-nitro-3-oxo-Y-naphthalene-1-sulphonate

Eriochrome Black T, also known as Solochrome Black T, is an indicator dye widely used in complexometric titrations, particularly for determining water hardness by detecting calcium and magnesium ions. Supplied by Loba Chemie in high-purity indicator grade, it appears as a dark violet to black powder and forms a wine-red complex with metal ions, which turns blue once the metal ions are fully chelated by EDTA. This compound is the sodium salt of a naphthalene-based azo dye, offering excellent solubility in water and consistent performance in analytical procedures. Its chemical name is Sodium 4-[(1-hydroxynaphthalen-2-yl-hydrazinylidene)]-7-nitro-3-oxo-naphthalene-1-sulphonate, with CAS number 1787-61-7, molecular formula C20H12N3NaO7S, molecular weight 461.38, and classified under HSN code 3204.9000.