Calcein is an indicator for the determination of calcium by titration with EDTA. The excitation wavelength and emission wavelength are 495/515 nm. It is suitable for fluorometric determination of calcium. It does not fluoresce in strong alkaline solution, but an intense fluorescence appears in the presence of alkaline earths, especially calcium. The yellow green fluorescence disappears instantly with an addition of EDTA. Also in acidic solution, the yellow green fluorescence of Calcein disappears with an addition of copper, zinc and mercury.