Due to the low atomic mass of boron, its different isotopes (B-10 and B-11) leads to a measurable impact on vibrational spectra. Indeed, a shift in the asymmetric stretching of the dissolved species has been found using attenuated total reflectance infrared spectroscopy, and those of acid species is higher than those of the borate ion (41 cm-1 vs. 20 cm-1 , respectively). A calibration from pure B-10 to pure B-11 boric acid has been performed, leading to an accuracy higher than 0.5% on the B-10 percentage of 0.1 M solution of mixtures of the two isotopes. Article Highlights-The isotope of boron has an impact on the infrared spectra of solutions-A difference of 14 cm-1 has been found using attenuated total reflectance infrared spectroscopy-The isotopic ratio of boron in boric acid can be measured after a calibration step