Fluorescein sodium

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An orange-red, Hygroscopic powder that is commonly called uranine. The sodium salt of fluorescein, discovered in 1871 by Baeyer, has an intense yellow-green Fluorescence under ultraviolet light. Like fluorescein, the water-soluble salt is used for the detection of soluble hydroxides, carbonates, and ammonia. It is sensitive to the part per billion level. Its UV absorption maximum occurs at 493.5 nm. Paper is dipped in soluble fluorescein solutions to form indicator strips, called Zellner's paper, that are sensitive to ammonia and other alkaline materials. Uranine is also used for dyeing Silk, Leather, Jute, nylon, and Wool.

Synonyms and Related Terms

soluble fluorescein; resorcinol phthalein sodium; resorcinolphthalein sodium; uranine; uranine yellow; D&C Yellow No.8; Acid Yellow 73; CI 45350; Fluorescite; Fluor-i-strip; Zellner's paper; disodium fluorescein; sodium fluorescein; soluble fluorescein;


  • Hygroscopic.
  • Contact may cause irritation.
  • Fisher Scientific: MSDS

Physical and Chemical Properties

  • Soluble in water. Slightly soluble in ethanol.
  • Maximum absorption wavelength = 493.5 nm.
Composition C20H12Na2O5
CAS 518-47-8
Molecular Weight mol. wt. = 376.05

Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 4194
  • Colour Index International online at www.colour-index.org Comment: discoverer