Adsorption behavior of hexafluorophosphate on selected bonded phases

The adsorption behavior of ammonium hexafluorophosphate was studied on four HPLC columns packed with adsorbents of different ability for dispersive interactions using frontal chromatography with LC/MS detection in negative ESI mode. Hexafluorophosphate (PF6−) adsorption isotherms were measured from acetonitrile/water and methanol/water mixtures. Increased PF6− adsorption with increased acetonitrile content was found between 0 and 15% of acetonitrile in the eluent. Further increase of the acetonitrile concentration leads to an exponential decrease of PF6− adsorption. Methanol, on the other hand, causes a steady decrease of PF6− adsorption with increased organic concentration in the mobile phase.