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  • F7250 - Fluorescein isothiocyanate isomer I

F7250 Sigma-Aldrich

Fluorescein isothiocyanate isomer I

suitable for protein labeling, ≥90% (HPLC), powder

Synonym: FITC, Fluorescein 5-isothiocyanate

  • CAS Number 3326-32-7

  • Empirical Formula (Hill Notation) C21H11NO5S

  • Molecular Weight 389.38

  •  Beilstein/REAXYS Number 1407295

  •  EC Number 222-042-0

  •  MDL number MFCD00005063

  •  PubChem Substance ID 24894933

  •  NACRES NA.47



Related Categories Antibodies, Antibody Labeling, Antibody Modification, Biochemicals and Reagents, Cell Biology,
Quality Level   200
assay   ≥90% (HPLC)
form   powder
application(s)   hematology: suitable
  histology: suitable
mp   >360 °C (lit.)
solubility   acetone: 1 mg/mL
fluorescence   λex 492 nm; λem 518 nm (green)
suitability   suitable for protein labeling
Featured Industry   Diagnostic Assay Manufacturing
storage temp.   2-8°C
SMILES string   Oc1ccc2c(Oc3cc(O)ccc3C24OC(=O)c5cc(ccc45)N=C=S)c1
InChI   1S/C21H11NO5S/c23-12-2-5-16-18(8-12)26-19-9-13(24)3-6-17(19)21(16)15-4-1-11(22-10-28)7-14(15)20(25)27-21/h1-9,23-24H


General description

Fluorescein isothiocyanate (FITC) is yellow-orange in color with an absorption maximum at 495nm. Upon excitation, it emits a yellow-green color with an emission maximum at 525nm.
It is widely used to attach a fluorescent label to proteins via the amine group. The isothiocyanate group reacts with amino terminal and primary amines in proteins. It has been used for the labeling of proteins including antibodies and lectins.
Fluorescein isothiocyanate isomer I has been proposed as a contact sensitizer.


Reagent for the FITC labeling of proteins; microsequencing of proteins and peptides (HPLC)
Biological applications include use as a fluorescent labeling reagent for proteins, a fluorescent reagent for protein tracing, and a reagent in the fluorescent antibody technique for the rapid identification of pathogens. It may be employed as the derivatization reagent for amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine and P-phenylethylamine in human urine during their capillary electrophoretic (CE) determination. It may be used for the preparation of fluorescent antibodies. It was employed for in vitro sensitization studies.

Reagent for the FITC labeling of proteins; Microsequencing of proteins and peptides (HPLC)


1, 5 g in glass bottle

50, 100, 250, 500 mg in glass bottle

Safety & Documentation

Safety Information

Personal Protective Equipment 
NONH for all modes of transport
WGK Germany 
Flash Point(F) 
Not applicable
Flash Point(C) 
Not applicable

Frequently Asked Questions

Which document(s) contains shelf-life or expiration date information for a given product?
If available for a given product, the recommended re-test date or the expiration date can be found on the Certificate of Analysis.
How do I get lot-specific information or a Certificate of Analysis?
The lot specific COA document can be found by entering the lot number above under the "Documents" section.
How do I find price and availability?
There are several ways to find pricing and availability for our products. Once you log onto our website, you will find the price and availability displayed on the product detail page. You can contact any of our Customer Sales and Service offices to receive a quote. USA customers: 1-800-325-3010 or view local office numbers.
What is the Department of Transportation shipping information for this product?
Transportation information can be found in Section 14 of the product's (M)SDS.To access the shipping information for this material, use the link on the product detail page for the product.
After the FITC (e.g., Product No. F7250) is conjugated to the protein, what is the solution stability of the conjugated protein?
The stability of the conjugated protein will be essentially the stability of the unconjugated protein.Some conjugated proteins might be stable when stored at -20°C and other conjugated proteins will have better solution stability at 2-8°CIf the protein concentration is too low, this also has a negative effect upon the stability of the conjugated protein.
Is Product No. F7250, Fluorescein isothiocyanate isomer I,pharmaceutical grade?
No. The product is considered suitable for research use only.
How stable is FITC Isomer 1 (e.g., Product No. F7250) once conjugated to an antibody?
FITC can photo bleach fairly rapidly. The prepared solution should be stored in a dark container and protected from light. When viewing the antibody staining under a microscope, it is advisable to use subdued fluorescent light when possible. If the fluorescent light stays at one position for too long, photo bleaching is noticeable.
Is the intensity of FITC (e.g., Product No. F7250) pH dependent?
Yes; many articles have reported the pH dependence of the fluorescence of fluorescein derivatives. See the following references: Archives Biochem. Biophys., 133, 263 (1969); J. Immunol., 95, 1165 (1966); Archives Biochem. Biophys., 73, 1 (1958); Standard test for labeling efficiency of FITC with BSA: NCCLS Approved Standard: ASM-1, 2nd ed., June, 1975; Characterization of FITC-dyes by IR and TLC: Analytical Biochem., 29, 526 (1969); Fluorescent labeling of proteins: Proc. Nat. Acad. Sci., 72, 459 (1975); Amer. J. Pathol., 34, 1081 (1958); Fluorescent labeling of a lectin: Meth. Enzymol., 81, 65 (1982).
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