The distillate is collected in a quartz or platinum receiver containing dilute NaOH solution (see Section 11.2.1). The usual procedure is to add methanol and concentrated sulphuric acid to a dried sample, and heat the still in a glycerol- or oil-bath, gradually raising the temperature to about 120 ☌. An anhydrous medium promotes the quantitative formation and distillation of methyl borate (water hydrolyses the ester). When separating small amounts of boron, a quartz distillation apparatus should be used since laboratory glassware contains boron. 65 ☌) is the most common method of isolating boron before its spectrophotometric determination. Zygmunt Marczenko, Maria Balcerzak, in Analytical Spectroscopy Library, 2000 11.1.1 Distillationĭistillation of boron as the volatile trimethyl borate (b.p. Boron carbide is often mixed with aluminum and then processed into the desired shape. However, because boron itself is very brittle (and, therefore, nonmalleable) it must be combined or alloyed with a more workable material. Therefore, it finds application in nuclear reactors as control rods and protective shields. 10B has the ability to absorb slow neutrons to a great extent. This results in the average atomic mass being 10.8 amu. Naturally occurring boron consists of two isotopes, 10B, which comprises about 20% and 11B, which makes up the remaining 80%. However, all of the structures are extremely rigid, resulting in boron having a hardness of 9.3 compared to the value of 10.0 for diamond (Mohs' scale). The arrangement of B 12 units in these structures is rather complex and they will not be shown here. The crystalline forms of boron are tetragonal, α-rhombohedral, and β-rhombohedral. These layers are stacked to give a three-dimensional structure. The B 12 units are surrounded by six others in a hexagonal arrangement with other layers similarly arranged lying above and below. The icosahedral arrangement of the B 12 structural unit.īoron cells may be considered as nearly spherical units and they can be arranged in more than one way in crystalline structures. While urine serves as the primary pathway for excretion of boron, bile, sweat, and exhaled breath constitute other routes of elimination.įigure 9.1. The kidneys are the primary site of homeostatic regulation of boron in the body, and at normal dietary or supplemental levels, there is no evidence for boron accumulation over time. Cessation of dietary boron results in a rapid drop in bone boron levels, with a direct relationship observed between ingestion and urinary excretion rates, which accounts for elimination of nearly 100% of the boron load. Boron metabolism in the body is not energetically feasible, with 523 kJ mol −1 energy being required to break boron–oxygen bonds. An oral dose of boron is readily and completely (approximately 95%) absorbed in humans and appears rapidly in the blood and body tissues. The decisive factor for the degree of liberation of boron from boron-containing topical products is the nature of the vehicle, with water-based vehicles resulting in higher boron levels achieved in blood and urine. While absorption through intact skin is negligible, it can occur through denuded or irritated skin. Betharia, in Encyclopedia of Toxicology (Third Edition), 2014 Toxicokineticsīoron-containing compounds can be absorbed from both the gastrointestinal and respiratory tracts, as indicated by an increase in levels of boron in the blood, tissues, or urine or by systemic toxic effects observed in the exposed individuals or laboratory animals.
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