USE OF INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY IN B-10 STABLE-ISOTOPE EXPERIMENTS WITH PLANTS, RATS, AND HUMANS

The commercial availability of inductively coupled plasma-mass spectro metry 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 fec al samples consists of 25 acid blanks, 1 digestion blank, 5 calibratio n solutions, 4 standard reference material solutions, 10 samples, and 4 natural abundance bias standards. Boron detection limits (3 x 1 sigm a) for acid blanks are 0.11 ppb for B-10. and 0.40 ppb for B-11. isoto pe ratios were measured in fecal samples with 20 to 50 ppb boron with <2% relative standard deviation. Rapid washout and minimal memory effe cts 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 w ashout. Boron isotope ratios in geological materials are highly variab le; apparently this variability is reflected in plants. The lack of a fixed natural abundance value for boron requires that a natural abunda nce ratio be determined for each sample or related data set. The natur al abundance variability also prevents quantitation and calculation of isotope dilution by instrument-supplied software. To measure boron tr ansport in animal systems, 20 mu g of B-10 were fed to a fasted rat. D uring 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 wi thin 3 hr (>90% recovery, 56% change in B-11/B-10) and returned to a n atural abundance ratio within 24 hr. in summary. boron concentrations and enriched isotope ratios have been measured successfully in rat uri ne and feces by using ICP-MS.