Determination of Total Fluoride in Boron-containing Solutions

Abstract

We describe a pretreatment method before determining the total fluoride in solutions containing tetrafluoroborate ion (BF₄⁻) with ion-selective electrodes (ISEs). BF₄⁻ was quantitatively converted to free fluoride by reacting with aluminum ions. The total fluoride concentration was then determined by ISE analysis without preliminary steam distillation using a tartrate- and tris(hydroxymethyl)methylamine (TRIS)-based total ionic strength adjustment buffer (TISAB). We investigated the effects of various factors on the decomposition of BF₄⁻ with aluminum ions, including the concentration of aluminum, pH, reaction temperature, and reaction time. The quantitative decomposition of BF₄⁻ was complete after 2 h at 50°C or 1 h at 70°C.