Column chromatographic boron isotope separation at 5 and 17 MPa with diluted boric acid solution.
Boron isotopic fractionation factor (S) between boron taken up in strongly basic anion exchange resin and boron in aqueous solution was determined by breakthrough column chromatography at 5 and 17 MPa at 25 degrees C, using 0.1 mM boric acid solution as feed solution. The S values obtained were 1.018 and 1.012, respectively, which were smaller than the value reported by using the same chromatographic method at the atmospheric pressure at 25 degrees C with the boron concentration of 10mM, but were larger than the values under the same condition with much higher concentration of 100 and 501 mM. Calculations based on the theory of isotope distribution between two phases estimated that 21% (5 MPa) and 47% (17 MPa) of boron taken up in the resin phase was in the three-coordinated B(OH)(3)-form, instead of in the four-coordinated B(OH)(4)-form, at high pressures even with a very diluted boric acid solution. We discussed the present results by introducing (1) hydration and (2) a partial molar volume difference between isotopic molecules. Borate may have been partially dehydrated upon transfer from the solution phase to the resin phase at high pressures, which resulted in smaller S values compared with those at the atmospheric pressure. Instead, it may be possible that the difference in the isotopic partial molar volume difference between B(OH)(3) and B(OH)(4)(-) caused the S value to decrease with increasing pressure.
Musashi
Masaaki
M
Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan. musashi@esa.c.u-tokyo.ac.jp
Oi
Takao
T
Matsuo
Motoyuki
M
Nomura
Masao
M
D001888:Boric Acids / Q000032:analysis*; D001895:Boron / Q000032:analysis*; D005591:Chemical Fractionation / Q000379:methods*; D002852:Chromatography, Ion Exchange / Q000379:methods*; D007554:Isotopes / Q000032:analysis; D011312:Pressure
D001888:Boric Acids; D007554:Isotopes; D001895:Boron; C032688:boric acid