A fluorescence probe dye is introduced into a cell, and excitation beams at three defferent wavelengths are irradiated to the cell to measure intensities of the fluorescence generated by the excitation beams, corresponding to the three wavelengths. Then, an equilibrium reaction equation for concentrations of the fluorescence probe dye, protein, free ions and their complexes in the cell, and a relationship equation between the fluorescence probe dye, protein, free ions and their complexes are used as simultaneous equations to give concentrations of the respective components. This process can correct interactions among various components of the cell due to bonding among them and a correct ion concentration can be determined.
Method for measurement of intracellular ion concentration using fluorescence probe dyes