Considerations in the determination of boron at low concentrations

Abstract

Experimental evidence now supports the nutritional essentiality of boron (B) in some biological systems, and accordingly, the need for reliable analytical B data is increasing. However, the accurate determination of B in biological materials is a formidable challenge at low concentrations (<1 mg B/kg). Recent studies still show significant analytical discrepancies in the analysis of animal tissues and fluids, despite the development of instrumental techniques such as TIMS, ICP-MS, ICP-ES, ICAP, SIMS, NA-MS, PGAA, NRA, and so forth, which have demonstrated detection limits approaching or exceeding (microg B/kg concentrations. Since boric acid is both volatile and ubiquitous in nature, the chemical and physical pathways for B contamination and its loss are manifold, especially during sample preparation. An added obstacle is the inadequacy of biological reference materials certified for B below 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 problems associated with the analysis of B from biological sources. Topics that are discussed include contamination from Teflon vessels during microwave digestion, losses owing to freeze-drying, B isotopic variations, standards preparation, reagent backgrounds, and instrumental interferences.

Analytical challenges of low level boron analysis in biological matrices

“…Although removal of particulates by filtration may be acceptable, unless the filter has been carefully cleaned prior to use, boron from even a new filter can introduce contamination. Consequently, boron can leach from the filter into the filtrate, thus elevating the boron concentration as much as 10 or more g/kg in volumes of a few milliliters [19]. In addition, if the filter is treated to make it basic, the filter then can remove measurable amounts of boron from the solution being filtered.…”

Boron in the Environment

“…20, 21 Sah and Brown 22 have made a comprehensive review of published methods of sample preparation, determinant purification, and determination of B in samples. Several techniques are routinely employed to analyze B in geochemical and biological matrices, but only few are sensitive enough to study B at trace level (<1 ppm).…”

“…20 That is why data on trace elements, including B, published before the introduction of clean procedures since approximately the mid-1970s should be considered carefully. 20 That is why data on trace elements, including B, published before the introduction of clean procedures since approximately the mid-1970s should be considered carefully.…”

Boron in humus and inorganic components of Hamra and Grumosol soils irrigated with reclaimed wastewater

“…Lindsay (1972) expressed this premise in a cautious way: 'Only two soluble B species in soils can be expected'. Moreover, until recently there were not adequate analytical facilities to determine B concentrations at trace (mg/g) level (Downing et al 1998), and especially to distinguish B chemical species in soil solution directly. Moreover, most experiments-either in hydroponics or in the field-on B behaviour in soil and biota have been based on supplying inorganic solutions of boric acid and borates.…”