The commercial availability of inductively coupled plasma-mass spectrometry technology (ICP-MS) has presented the opportunity to measure the boron concentrations and isotope ratios in a large number of samples with minimal sample preparation. A typical analytical sequence for fecal samples consists of 25 acid blanks, 1 digestion blank, 5 calibration solutions, 4 standard reference material solutions, 10 samples, and 4 natural abundance bias standards. Boron detection limits (3 x 1 sigma) for acid blanks are 0.11 ppb for B-10. and 0.40 ppb for B-11. isotope ratios were measured in fecal samples with 20 to 50 ppb boron with <2% relative standard deviation. Rapid washout and minimal memory effects were observed for a 50 ppb beryllium internal standard, but a 200 ppb boron biological sample had a 1.0 ppb boron memory after a 6-min washout. Boron isotope ratios in geological materials are highly variable; apparently this variability is reflected in plants. The lack of a fixed natural abundance value for boron requires that a natural abundance ratio be determined for each sample or related data set. The natural abundance variability also prevents quantitation and calculation of isotope dilution by instrument-supplied software. To measure boron transport in animal systems, 20 mu g of B-10 were fed to a fasted rat. During the 3 days after a B-10 oral dose, 95% of the B-10 was recovered from the urine and 4% from the feces. Urinary isotope ratios, B-11/B-10, changed from a natural abundance of 4.1140 to an enriched Value of 0.9507, a 77% change. The B-10 label in perfused rat livers peaked within 3 hr (>90% recovery, 56% change in B-11/B-10) and returned to a natural abundance ratio within 24 hr. in summary. boron concentrations and enriched isotope ratios have been measured successfully in rat urine and feces by using ICP-MS.
