A dispersive liquid–liquid microextraction procedure for determination of boron in water after ultrasound-assisted conversion to tetrafluoroborate

A novel, simple and green procedure is presented for the determination of boron. The method is based on ultrasound-assisted conversion of boron to tetrafluoroborate anion and the formation of an ion pair between BF4− and Astra Phloxine reagent (R), followed by dispersive liquid–liquid microextraction of the ion pair formed and subsequent UV–vis spectrophotometric detection. The conversion of boron to tetrafluoroborate anion is performed in an acidic medium of 0.9molL−1 H2SO4 in the presence of 0.1molL−1F– by means of 10min of ultrasonication. The extraction of the ion pair formed between BF4− and R (1×10−4molL−1R) is carried out by dispersive liquid–liquid microextraction using 0.5mL of amyl acetate (as extraction solvent), tetrachloromethane (as auxiliary solvent) and acetonitrile (as dispersive solvent) in a ratio of 1:1:2. The absorbance of the coloured extracts obeys Beer's law in the range 0.22–18.7mgL−1 of B(III) at 553nm wavelength. The limit of detection calculated from a blank test (n=10) based on 3s is 0.015mgL−1 of B(III). The method was applied to the determination of boron in mineral waters.