Acid dyes

pH indicator

Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. It is used as a fluorescent tracer in many applications.

Tartrazine is a synthetic lemon yellow azo dye primarily used as a food coloring. It is also known as E number E102, C.I. 19140, FD&C Yellow 5, Yellow 5 Lake, Acid Yellow 23, Food Yellow 4, and trisodium 1-(4-sulfonatophenyl)-4-(4-sulfonatophenylazo)-5-pyrazolone-3-carboxylate.

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Azorubine, also known as carmoisine, is an azo dye consisting of two naphthalene subunits. It is a red solid. It is mainly used in foods that are heat-treated after fermentation. It has E number E122.

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tetrachloro-tetraiodo-fluorescein used as stain

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dye that is typically applied to animal-fiber or synthetic-fiber textiles in an acidic solution

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