Abstract
The present paper deals with the research on the optimal conditions for the formation of fluoroborate as an analytical form of boron. Despite numerous scientific publications related to the determination of boron using various methods involving [BF4]ˉ ions as an analytical form, the conditions for obtaining the latter differ significantly. This difference is likely due to the complexity of the H3BO3-F--H3O+ system, where polymolecular forms of hydrofluoric acid can exist. Factors such as the inability to measure pH using a glass electrode, the velocity of the complexation process, and the requirement for specialized labware and equipment resistant to aggressive environments contribute to this complexity. In this study, potentiometry with PVC plasticized [BF4]ˉ - sensors, known for their metrological and operational characteristics, was used as a convenient tool to investigate such systems. The [BF4]ˉ - selective electrode based on the electroactive substance ion pair 2-(N-ethylcarbazole-3)-ethenyl-1,3,3-trimethyl-3H-indole tetrafluoroborate, which retains its metrological characteristics in acidic and strongly acidic environments and exhibits selectivity up to F-(= -4. 0), was employed as a sensor.
 The sensor allowed for the study of [BF4]ˉ - complex formation under different reaction conditions by recording kinetic curves in EMF-time coordinates. The yield of the analytical form was estimated at different concentrations of acid, fluoride ions, and temperature. The obtained data were used to construct the yield surface of tetrafluoroborate, revealing that the optimal conditions for the formation and stability of tetrafluoroborate at room temperature are a medium of 1 M sulfuric acid and 0. 25 M NH4F. Under these conditions, the yield of [BF4]ˉ reaches 99% within 10 minutes. Although the use of phosphoric acid does not allow for the attainment of an appropriate yield of the analytical form under equilibrium conditions, its low process velocity makes it suitable for kinetic - potentiometric determination of boron. This characteristic was utilized to develop a method for the determination of boron in phosphoric acid using the fixed-time method.
 Keywords: tetrafluoroborate ion; potentiometric sensor; kinetic determination of boron.
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