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6-Carboxyfluorescein | CAS 3301-79-9

A 6-carboxy fluorescein label precursor combining a xanthene chromophore with a free carboxyl handle, where positional-isomer identity and solution-dependent optical response guide material qualification.

CAS3301-79-9
Molecular formulaC21H12O7
Molecular weight376.3 g/mol

Product overview

The added carboxyl group gives 6-carboxyfluorescein a site for preparing fluorescent conjugates. CAS 3301-79-9 identifies the 6-isomer, rather than a 5/6 mixture or an activated ester. The chromophore and coupling group require separate review: HPLC addresses chemical and isomeric composition, while optical measurements need stated solvent and pH.

Chemical identity

Chemical name
6-Carboxyfluorescein
CAS number
3301-79-9
Molecular formula
C21H12O7
Molecular weight
376.3 g/mol

Application context

6-FAM is used in fluorescent-label chemistry and spectroscopy. The free acid serves as a precursor for coupling derivatives, allowing a fluorescein signal to be incorporated into a chosen molecular system. For assay development, compare absorption or fluorescence under the intended solution conditions and evaluate the resulting conjugate separately. Specify whether the project requires free 6-FAM or an activated derivative before selecting a grade.

Chemistry and synthetic role

The fluorescein framework provides the chromophore, while the additional carboxyl group is available for derivatization.

Quality review

Separate 5- and 6-isomers

Request a method that establishes the selected positional isomer.

Define optical test conditions

Record solvent, pH and concentration for absorption or fluorescence comparisons.

Clarify water and assay basis

Confirm whether dye content is reported as received or corrected for water.

Preparing a specification

Specify free-acid 6-FAM, isomer-resolving HPLC, dye-content basis, water and optical test conditions appropriate to the target assay.

Packaging and storage

Confirm container compatibility, closure and net weight for the selected grade and destination. Follow the actual supplier SDS and batch label for storage and transport.

Documentation

Request the batch COA, SDS and analytical methods covering the agreed purchasing specification. Confirm which supporting chromatograms and application-specific records are available from the selected manufacturer.

Procurement questions

Is this an NHS ester?

No. It is free 6-carboxyfluorescein and requires a suitable coupling strategy.

Can a 5/6 mixture replace it?

Only if the project accepts mixed positional isomers and qualifies the resulting conjugate.

Why must spectral conditions be stated?

Fluorescein optical response depends on its solution environment.

Technical sources
  1. PubChem CAS identity lookupNCBI / PubChem
  2. 6-Carboxyfluorescein C2478TCI