Abstract

By monitoring atomic fluorine at mass 19, fluoride ions in aqueous samples were determined by utilising an inductively coupled plasma (ICP) quadrupole mass spectrometer. In order to prevent the decrease in the ionisation efficiency of fluorine atom caused by introduction of water mist, electrothermal vaporisation was used for sample introduction into the ICP. To prevent the loss of fluorine during the drying process, a small amount of tetramethylammonium hydroxide solution was placed as a chemical modifier into a tungsten boat furnace. After the evaporation of the solvent, the analyte instantly vaporised and was then introduced into the ICP ion source to detect the ¹⁹F⁺ ion signal. By applying an extreme distance from the ion source to the inlet orifice of the sampling cone, the molecular ¹⁸OH⁺ ion which would interfere in the detection of the¹⁹F⁺ ion was completely degraded. By using this system, the detection limit (3σ) of 0.29 µg of the aqueous fluoride ion was achieved. The calibration curve was linear in the tested range of up to 100 µg of the fluoride ion. The relative standard deviation for ten replicate measurements was 3.6% for 5.0 µg of the fluoride ion.