Separation and preconcentration of fluoride at the ng ml−1 level with a polymer complex of zirconium(IV) followed by potentiometric determination in a flow system Original Research Article

A complex of Zr(IV) with a hydrophilic resin having an iminodiacetic acid group rapidly and selectively adsorbed fluoride from acidic media, which was reversibly expelled on increase in pH. A flow system consisting of a mini-column packed with this polymer complex for separation and preconcentration of fluoride and an ion-selective electrode for detection gave the same peak height for the same amount of fluoride, irrespective of the sample concentration and volume, and thus could be calibrated based on the chemical amount; the detection limit defined by S/N=3 was 0.1 nmol. Use of the flow system decreased the lower limit for quantitative adsorption of fluoride down to 5×10−8 M (compared with 1×10−4 M by batch adsorption), and drastically increased the tolerance limits of interfering cations and anions; even the presence of a fourfold molar ratio of Al3+ was tolerated with cyclohexane diamine tetraacetic acid as masking reagent. This system was applied to the determination of fluoride in drinking water and concentrated brine. The adsorption and desorption mechanism is discussed in detail.