Considerations in the determination of boron at low concentrations

Experimental evidence now supports the nutritional essentiality of boron (B ) in some biological systems, and accordingly, the need for reliable analyt ical B data is increasing. However, the accurate determination of B in biol ogical materials is a formidable challenge at low concentrations (<1 mg B/k g). Recent studies still show significant analytical discrepancies in the a nalysis of animal tissues and fluids, despite the development of instrument al techniques such as TIMS, ICP-MS, ICP-ES, ICAP, SIMS, NA-MS, PGAA, NRA, a nd so forth, which have demonstrated detection limits approaching or exceed ing (mu gB/kg concentrations. Since boric acid is both volatile and ubiquit ous in nature, the chemical and physical pathways for B contamination and i ts loss are manifold, especially during sample preparation. An added obstac le is the inadequacy of biological reference materials certified for B belo w mg B/kg. With an emphasis toward sample preparation and ICP-MS analysis, examples are provided in this article to help the analyst avoid common prob lems associated with the analysis of B from biological sources. Topics that are discussed include contamination from Teflon vessels during microwave d igestion, losses owing to freeze-drying, B isotopic variations, standards p reparation, reagent backgrounds, and instrumental interferences.