Application of Automatic Potentiometric Titration of Boron Concentration in the Determination of Boron Isotope Separation Effect Based on MOFs

Metal-organic frameworks (MOFs) as adsorbents to separate boron isotope method is increasingly attractive. In order to systematically study the boron isotopic effect, an automatic potentiometric titration method for the determination of the boron concentration of boric acid in the solution was established, and taking several MOFs as examples to determine their separation effect on boron isotope. First, using weak acid fortification method, the dosage of mannitol was four times of the theoretical dosage. The difference between the measured value of the boric acid standard material and the reference value was the smallest (-0.000 13 g), the measurement uncertainty of the method was 0.000 2-0.000 8, and the measurement accuracy is 0.10%-0.40%,which made the method valid and reliable. Then, using established automatic potentiometric titration method to determine the boron concentration, using MC-ICP-MS to determine the boron isotope abundance ratio ^10/11B of the boric acid solution before and after adsorption, respectively. The static separation of boron isotopes by three MOFs, Cu-MOF-OCH₃, UiO-66-NH₂ and MIL-101(Cr)-2,3-OH, was determined as an example experiment. The results showed that the isotopic separation factors S of Cu-MOF-OCH₃, UiO-66-NH₂ and MIL-101(Cr)-2,3-OH for boron isotopes were 1.066, 1.037 and 1.079, respectively, which were all larger than that of the commercial resin Amberlite IR743 (1.027). Among them, Cu-MOF-OCH₃ has a positive isotopic effect on 10B cause of 10/11S＞1, and the UiO-66-NH₂, MIL-101(Cr)-2,3-OH have a positive isotopic effect on ¹¹B cause of ^11/10S＞1. This provides a reference for the systematic study of the separation effect of MOFs on boron isotopes.