Substoichiometric Isotope Dilution Mass Spectrometry of Boron by the Ion-Pair Extraction with Halogenated Salicyl Alcohol Derivatives and a Quaternary Ammonium Salt

Abstract

Novel salicyl alcohol derivatives (H₂X_nsal), 5-bromo-, 3,5-dibromo-, and 3,5-diiodosalicyl alcohol which were abbreviated to H₂Brsal, H₂Br₂sal, and H₂I₂sal, respectively, were synthesized and used for the selective extraction of boric acid. Boric acid was extracted with each H₂X_nsal into chlorobenzene containing trioctylmethylammonium chloride (TOMACl) as an ion-pair complex, TOMA·B(X_nsal)₂, at a different pH range. The extraction constant (K_ex) of boric acid was determined by the equilibrium analyses including the formation of hydrogen-bonded complex of each H₂X_nsal with TOMACl in the organic phase. The K_ex values obtained by salicyl alcohol (H₂sal) and its derivatives were decreased in the order of H₂I₂sal ≥ H₂Br₂sal > H₂Brsal > H₂sal. The most powerful extractant, H₂I₂sal, was employed for the substoichiometric extraction of boric acid, which was extracted at pH 5 – 9 with a substoichiometric amount of TOMACl in the presence of an excess of H₂I₂sal. The present substoichiometric separation method combined with the stable isotope dilution analysis using inductively coupled plasma mass spectrometry (ICP-MS) could be successfully applied to the determination of boron in a reference material of high-analysis compound fertilizer (FAMIC-A-08) without any correction as to the isotopic abundance.