Title: Fluorescein
CAS Registry Number: 2321-07-5
CAS Name: 3¢,6¢-Dihydroxyspiro[isobenzofuran-1(3H),9¢-[9H]xanthen]-3-one
Additional Names: 9-(o-carboxyphenyl)-6-hydroxy-3H-xanthen-3-one; 3¢,6¢-dihydroxyfluoran; 3¢,6¢-fluorandiol; 9-(o-carboxyphenyl)-6-hydroxy-3-isoxanthenone; resorcinolphthalein; D & C Yellow no. 7; C.I. Solvent Yellow 94; C.I. 45350:1
Molecular Formula: C20H12O5
Molecular Weight: 332.31
Percent Composition: C 72.29%, H 3.64%, O 24.07%
Literature References: Prepd by heating phthalic anhydride with resorcinol: Fischer, Bollmann, J. Prakt. Chem. 104, 123 (1922); McKenna, Sowa, J. Am. Chem. Soc. 60, 124 (1938). Structure: Ramart-Lucas, Compt. Rend. 205, 864 (1937); Nagase et al., J. Pharm. Soc. Jpn. 73, 1033, 1039 (1953). Review of synthesis, properties and histological use: R. F. Steiner, H. Edelhoch, Chem. Rev. 62, 457 (1962). Use as label in immunoassays: E. F. Ullman et al., J. Biol. Chem. 251, 4172 (1976); Y. Suzuki et al., Jpn. J. Exp. Med. 49, 179 (1979). Toxicity studies in fish: L. L. Marking, Prog. Fish Cult. 31, 139 (1969). Toxicity data: S. L. Yankell, J. J. Loux, J. Periodontol. 48, 228 (1977). See also: Colour Index vol. 4 (3rd ed., 1971) p 4424; H. J. Conn's Biological Stains, R. D. Lillie, Ed. (Williams & Wilkins, Baltimore, 9th ed., 1977) p 337.
Properties: Yellowish-red to red powder. mp 314-316° in sealed tube, with decompn. Insol in water, benzene, chloroform, ether. Sol in hot alcohol or glacial acetic acid; also sol in alkali hydroxides or carbonates with a bright green fluorescence appearing red by transmitted light. Absorption max: 493.5, 460 nm.
Melting point: mp 314-316° in sealed tube
Absorption maximum: Absorption max: 493.5, 460 nm
Derivative Type: Disodium salt
CAS Registry Number: 518-47-8
Additional Names: Soluble fluorescein; resorcinol phthalein sodium; uranin(e); uranine yellow; D & C yellow No. 8; C.I. Acid Yellow 73; C.I. 45350
Trademarks: Ak-Fluor (Akorn); Fluorescite (Alcon); Fluorets (Chauvin); Fluor-i-strip (Ayerst); Ful-Glo (Sola-Barnes-Hinds); Funduscein (IOLAB); Irescein (Americal)
Molecular Formula: C20H10Na2O5
Molecular Weight: 376.27
Percent Composition: C 63.84%, H 2.68%, Na 12.22%, O 21.26%
Properties: Hygroscopic orange-red powder. Freely sol in water with yellowish-red color and intense yellowish-green fluorescence perceptible down to a dil of 0.02 ppm under uv light. The fluorescence disappears when the soln is made acid, and reappears when the soln is again made neutral or alkaline. Absorption max (water): 493.5 nm. Slightly sol in alc. LD50 in mice, rats (mg/kg): 4738, 6721 orally (Yankel, Loux).
Absorption maximum: Absorption max (water): 493.5 nm
Toxicity data: LD50 in mice, rats (mg/kg): 4738, 6721 orally (Yankel, Loux)
Use: In examining subterranean waters. Serves to ascertain source of springs, connections between streams and sea, determining approx vol of water delivered by a spring, detecting source of contamination of drinking water, infiltration of soil with waste waters of factories. In externally applied drugs and cosmetics. Analytical reagent (protein label). Clinical reagent (immuno-histological stain, immuno-fluorescent label).
Therap-Cat: Diagnostic aid (corneal trauma indicator), ophthalmic angiography, contact lens fitting.
Therap-Cat-Vet: Diagnostic aid (corneal lesions, intra-ocular inflammation).
Keywords: Diagnostic Aid.
Fluorescein Paper Fluorescin Fluoresone Fluoridamid Fluorine Dioxide

Skeletal formula
Ball-and-stick model
Sample of dark red powder
CAS number 2321-07-5 YesY
PubChem 16850
ChemSpider 15968 YesY
EC number 219-031-8
DrugBank DB00693
KEGG D01261 YesY
MeSH Fluorescein
ChEBI CHEBI:31624 YesY
ATC code S01JA01
Jmol-3D images Image 1
Molecular formula C20H12O5
Molar mass 332.31 g mol−1
Density 1.602 g/mL
Melting point 314 to 316 °C; 597 to 601 °F; 587 to 589 K
Solubility in water Slightly
S-phrases S26 S36
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Fluorescein is a synthetic organic compound available as a dark orange/red powder slightly soluble in water and alcohol. It is widely used as a fluorescent tracer for many applications.

Fluorescein is a fluorophore commonly used in microscopy, in a type of dye laser as the gain medium, in forensics and serology to detect latent blood stains, and in dye tracing. Fluorescein has an absorption maximum at 494 nm and emission maximum of 521 nm (in water). The major derivatives are fluorescein isothiocyanate (FITC) and, in oligonucleotide synthesis, 6-FAM phosphoramidite.

Fluorescein also has an isosbestic point (equal absorption for all pH values) at 460 nm. Fluorescein is also known as a color additive (D&C Yellow no. 7). The disodium salt form of fluorescein is known as uranine or D&C Yellow no. 8.

The color of its aqueous solution varies from green to orange as a function of the way it is observed: by reflection or by transmission, as it can be noticed in bubble levels in which fluorescein is added as a colorant to the alcohol filling the tube to increase the visibility of the air bubble and the precision of the instrument. More concentrated solutions of fluorescein can even appear red.