Boron determination in water by ion-selective electrode

Abstract

The fluoroborate electrode shows a linear Nernstian response down to 0.35 mg/L of boron (B) and can be reproducibly calibrated to 0.001 mg/L B. Reproducibility at 0.1 and 1.0 mg/L of B is better than 0.5%. Electrode sensitivity declines significantly below 0.035 mg/L B, and this is the practical detection limit. Minimum equilibrium times increase with decreasing concentration, from 1 min at 5.0 mg/L to 10 min at <0.05 mg/L of B. A pH hysteresis effect was observed between pH 2–12. Effects of pH are minimised if analyses are performed between pH 3.5 and 5.0. Prolonged storage of fluoroborate solutions results in a loss of the ion from the solution. In both glass and plastic containers, a decrease of up to 16% in concentration was observed for concentrations of 0.1, 1.0, and 10.0 mg/L of B over a two-week period. Acid washing containers did not prevent boron loss. Fluoroborate ion formation, following addition of hydrofluoric acid to the sample, requires about 2 h. Samples should not be analysed before this complexation time has elapsed.