Fast determination of tetrafluoroborate by high-performance liquid chromatography using a monolithic column

Fast determination of tetrafluoroborate by high-performance liquid chromatography using a silica-based monolithic column and direct conductivity detection was carried out. Chromatographic separation was performed on a Chromolith Speed ROD RP-18e column (50 mm × 4.6 mm i.d.) with tetrabutylammonium hydroxide (TBA-OH) + phthalic acid as eluent. The effects of eluent concentration, eluent pH, column temperature and flow rate on retention time of tetrafluoroborate were investigated. The optimized chromatographic conditions for determination of tetrafluoroborate were using 0.5 mM TBA-OH + 0.31 mM phthalic acid (pH 5.5) as eluent, column temperature of 30 °C and flow rate of 6.0 mL/min. Retention time of tetrafluoroborate was less than 1 min under the conditions. Common anions (Cl−, Br−, NO3− and SO42−) did not interfere with the determination of tetrafluoroborate. Detection limit (S/N = 2) for tetrafluoroborate was 1.4 mg/L. The linear range of calibration curve between peak area and the concentration of tetrafluoroborate was from 1.4 to 100.0 mg/L. The reproducibility was 0.09% and 1.8% (n = 5) relative standard deviation (RSD) for retention time and peak area, respectively. The method has been applied to the determination of tetrafluoroborate in ionic liquids. Recoveries of tetrafluoroborate after spiking were 98.2–101.5%.