AMCA-X, SE is one of the most popular blue fluorescent tagging molecules. It is widely used to label antibodies, proteins and small drug molecules. AMCA-X succinimidyl ester contains a seven-atom aminohexanoyl spacer between the fluorophore and the reactive group. This spacer separates the fluorophore from the biomolecule to which it is conjugated, potentially reducing the quenching that typically occurs upon conjugation. AMCA fluorescence can be detected at the emission wavelength of 442±10 nm when excited at 353±10 nm. The AMCA-protein conjugates are suitable for immunofluorescent staining, in situ hybridization, flow cytometry and other biological applications. The kit has all essential components for performing the conjugation reaction and for purifying the AMCA-protein conjugates. The kit is able to perform three conjugation reactions with each reaction labeling up to 5 mg IgG.