MEASUREMENTS OF THE ISOTOPIC RATIO OF BORON.

A method of boron isotope analysis using the M2BO2+ ion(M is the alkaline metal)has been investigated. In the case of the M2BO2+ where the alkaline metal has two or more isotopes, this method has the following characteristics.(1)Three or more peaks are obtained from the combination of isotopes of boron and the alkaline metal.(2)Using the enriched isotopes of the alkaline metal, the relative peak heights can be adjusted so as to read with minimum errors.(3)The discrimination effect may be corrected from the known isotopic composition of the alkaline metal.(4)The error of measurements can be examined by a pair of the appropriate combination of peak heights. As results of the investigation on a series of alkaline borates, it was concluded that the Rb2BO2+ ion has the most appropriate combination of peak heights. In the case of Rb2BO2+, four peaks of m/e 212-215 are effectively obtained. The error of measurements can be examined from the relation 213/212=215/214. The discrimination effect for the measured boron isotopic ratio it 11B/10B=213/212 may be corrected using the measured value of 215/213=87Rb/85Rb+18O/16O and the standard isotopic ratio of rubidium and oxygen. In this method, the examination of the error of measurements is always feasible, but the correction of the discrimination effect may be significant only when the deviation of the observed value due to the discrimination effect is greater than the statistical fluctuation or the variation of the standard isotopic composition due to the fractionation effect.