Basic study on the determination of total boron by conversion to tetrafluoroborate ion (BF4) followed by ion chromatography |
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Authors: | Junya Katagiri Tadaaki Mizoguchi |
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Institution: | a Environment Conservation Research Institute, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba-ku Sendai 980-8579, Japan b Graduate School of Environmental Studies, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba-ku Sendai 980-8579, Japan |
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Abstract: | The basic study on the determination of tetrafluoroborate ion (BF4−) by ion chromatography, and total boron by conversion of boric acid to BF4− followed by ion chromatography of BF4− has been carried out. The results of thermodynamic calculations for the system of boric acid (H3BO3)-F−-H+ showed that the mole fraction of BF4− was higher than 99% at pH lower than 3.5 and 4.5 when the total free fluoride concentration (2H2F2] + 2HF2−] + HF] + F−]) was as high as 0.1 and 1.0 M, respectively. The fraction of BF4− increased with increasing total free fluoride concentration. BF4− fraction values were higher than 99% at pH 0.75 and at total free fluoride concentration of 0.05 M or higher. BF4− was hardly formed at pH > 7 even when the total free fluoride concentration was as high as 1.0 M. According to the experimental results, the fraction of BF4− at pH 0.7-0.8 was 51.2, 95.6 and 96.7% when the total fluoride concentration (2H2F2] + 2HF2−] + HF] + F−] + 3BF3OH−] + 4BF4−]) was 0.2, 1.0 and 3.3 M, respectively. The formation reaction of BF4− from boric acid reached an equilibrium state within 20 min regardless of reaction temperature, in the range of 20-50 °C, when the total boron and total fluoride concentrations were 66.7 mM and 1.0 M, respectively. Although BF4− was formed only under acidic conditions, BF4−, once formed, was very stable under alkaline conditions at least for several hours. We have concluded that BF4− could be analyzed by ion chromatography using sodium hydroxide solution as an eluent because BF4− was stable under chromatographic conditions. BF4− solution prepared from boric acid could be used as a standard solution in the ion chromatographic analysis of BF4− instead of the sodium tetrafluoroborate (NaBF4) reagent available commercially, if a discrepancy of about 4-5% was allowed. |
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Keywords: | Tetrafluoroborate ion Boron Fluorine Analysis Ion chromatography |
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