The application of ultrasound for the improvement of analytical procedures: Determination of boron

Abstract

The aim of the presented study was to investigate the use of ultrasonic irradiation for the improvement of analytical methods. A procedure for boron determining based on the conversion of boric acid to tetrafluoroborate and subsequent spectrophotometric detection, previously reported from our laboratory, was used as a model. The optimum conditions for the conversion of boron to tetrafluoroborate anion (0.9 mol L⁻¹ H₂SO₄, 0.1 mol L⁻¹ F⁻, 7 min ultrasonication) as well as for complex formation and extraction of BF₄⁻ with DIC (1 × 10⁻⁴ mol L⁻¹ DIC) were found. The absorbance of the coloured extracts obeys Beer's law in the range 0.1–1.0 mg L⁻¹ of B. The limit of detection calculated from a blank test (n = 10; P = 0.95) based on 3 s is 0.02 mg L⁻¹ of B. The procedure was applied to the analysis of mineral waters and a pharmaceutical preparative. The main advantage of ultasonification is that the conversion process occurs much faster; reaction time therefore decreases from 30 min to 7 min. Moreover, it does not lead to the heating of the sample, meaning, as a consequence, the value of the blank test decreases, and the reaction does not have to be performed in a closed system.