Isosbestic point
（重定向自Isosbestic）
![Isosbestic point in the bromocresol green spectrum. The spectra of basic, acid and intermediate pH solutions are shown. The analytical concentration of the dye is the same in all solutions.](/Images/godic/202501/21/Bromocresol_green_spectrum2408.png")
![Isosbestic point as is used in oximetry.](/Images/godic/202501/21/Isobestic_graph2408.gif")
In spectroscopy, an isosbestic point is a specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample. The word derives from two Greek words: "iso", meaning "equal", and "sbestos", meaning "extinguishable".