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Fluorescein isothiocyanate isomer I

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

FITC, Fluorescein 5-isothiocyanate
Empirical Formula (Hill Notation):
CAS Number:
Molecular Weight:
EC Number:
MDL number:
PubChem Substance ID:

Quality Level


≥90% (HPLC)




>360 °C (lit.)


acetone: 1 mg/mL


λex 492 nm; λem 518 nm (green)


suitable for protein labeling


diagnostic assay manufacturing

storage temp.


SMILES string




InChI key


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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)


50, 100, 250, 500 mg in glass bottle
1, 5 g in glass bottle


Health hazard

Signal Word


Hazard Statements

Hazard Classifications

Resp. Sens. 1 - Skin Sens. 1

Storage Class Code

11 - Combustible Solids



Flash Point(F)

Not applicable

Flash Point(C)

Not applicable

Personal Protective Equipment

dust mask type N95 (US), Eyeshields, Gloves

Certificate of Analysis

Enter Lot Number to search for Certificate of Analysis (COA).

Certificate of Origin

Enter Lot Number to search for Certificate of Origin (COO).

  1. 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.

  2. 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.

  3. 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.

  4. 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. 

  5. 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°C  If the protein concentration is too low, this also has a negative effect upon the stability of the conjugated protein.

  6. Is Product No. F7250, Fluorescein isothiocyanate isomer I, pharmaceutical grade?

    No. The product is considered suitable for research use only.

  7. 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.

  8. 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).

  9. My question is not addressed here, how can I contact Technical Service for assistance?

    Ask a Scientist here.

Test of a two-pathway model for small-solute exchange across the capillary wall.
The American Journal of Physiology, 274, H2062-H2062 (1998)
Human monoclonal autoantibodies specific for the bullous pemphigoid antigen 1 (BPAg 1).
Peyron E
Journal of Immunology, 153, 1333-1333 (1994)
Vaccines: Recent Trends and Progress (2012)
Structural mechanisms of acute VEGF effect on microvessel permeability.
Fu BM and Shen S
American Journal of Physiology. Heart and Circulatory Physiology, 284, H2124-H2124 (2003)
Chromatographically pure fluorescein and tetramethylrhodamine isothiocyanates.
L C FELTON et al.
Analytical biochemistry, 2, 178-180 (1961-04-01)


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