Zirconia as a Fluoride Selective Stationary Phase for Ion Chromatography

Fluoride has long been important as an environmental analyte, however, it has seen a recent surge of interest with increasing concerns surrounding per/polyfluoroalkyl substances (PFAS) and their surrogate measurement as adsorbable organic fluorine (AOF) by combustion ion chromatography. Separation of fluoride from both the void peak and other common weakly retained species via anion exchange chromatography is difficult. Although gradient elution on high-capacity ion exchange phases can separate fluoride from the void, separation of fluoride in complex samples remains a challenge. We describe the use of zirconia (ZrO2) as a fluoride selective stationary phase in anion chromatography. Zirconia has been used in normal phase high performance liquid chromatography (HPLC); however, we find that it has a strong, near exclusive affinity for fluoride among monovalent anions when used as a stationary phase in ion chromatography (IC). Zirconia provides facile separation of fluoride from the void peak and other weakly retained ions on traditional anion exchange phases. This permits zirconia columns as short as 10 mm to be used as fluoride preconcentrators, improving limits of detection and quantitation for fluoride by IC. The use of zirconia as a stationary phase in IC has the potential to push the boundaries of fluoride determination being demanded by new PFAS screening methods seeking limits of detection at the parts per trillion level.