Dispersive liquid–liquid micro extraction of boron as tetrafluoroborate ion (BF4−) from natural waters, wastewater and seawater samples and determination using a micro-flow nebulizer in inductively coupled plasma-quadrupole mass spectrometry

Abstract

Boron, present in groundwater and seawater, is extracted as tetrafluoroborate anion by dispersive liquid–liquid microextraction (DLLME) and determined by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). A low flow rate (200 μL min⁻¹) SeaSpray™ micro-flow nebulizer was used for the sample introduction. In this method, the tetrafluoroborate anion formed in the presence of 0.9 mol L⁻¹ H₂SO₄ and 0.1 mol L⁻¹ F⁻ was extracted into chloroform in the presence of Aliquat® 336 (tricaprylmethylammonium chloride) at room temperature. The bulky cationic surfactant, Aliquat® 336, acts as a phase transfer agent, which not only forms an ion-pair complex with tetrafluoroborate anion but also helps in the rapid conversion of boric acid to BF₄⁻ ion. The tetrafluoroborate anion was back-extracted from the chloroform layer with nitric acid for determination by ICP-QMS. Effective parameters for the complex formation and its extraction, such as volume of extractant/disperser solvent, extraction time and concentration of the surfactant have been optimized. Under optimum conditions, an average preconcentration factor of 18 was obtained for 8 mL of water sample for determination by ICP-QMS. The calibration graph was linear in the range of 1–50 μg L⁻¹ for boron, with a limit of detection of 0.3 μg L⁻¹, calculated based on 3 s of blank (n = 6). The precision was close to 3% R.S.D. (n = 3), when processing 8 mL aliquots of sample. The method has been applied to determine boron in bottled mineral water, groundwater, wastewater and seawater samples. The recoveries obtained for the boron spiked to 30 μg L⁻¹ levels in these water samples were 97–102%.