A rapid impregnation method for loading desired amounts of extractant on prepacked reversed-phase columns for high performance liquid chromatographic separation of metal ions.

A time-efficient impregnation method for loading extractant onto reversed-phase columns was developed, using di-(2-ethylhexyl) phosphoric acid (HDEHP) as a model extractant. The optimal loading conditions for the impregnation process of a standard analytical scale column was achieved by dissolving an appropriate amount of HDEHP (per void volume) in n-pentane, flushing the column with two void volumes (5mL) of impregnation solution and heating the column for a short time to remove the solvent. The process takes about one hour, a significant time reduction compared to commonly used impregnation methods (17-23h). The chromatographic traits for separation of the lighter lanthanides (La-Gd) using columns impregnated under different conditions were evaluated; heating for short period of time gave improved column performance most likely due to the presence of n-pentane in the pores of the support material. A linear relation was found (R2=0.9934) for the amount of HDEHP loaded as a function of HDEHP concentration in the impregnation solution. The coated amounts of HDEHP were in the range of 0.29-2.25mmol per column by flushing with 5mL of impregnation solution containing 0.3-5.0mmol of HDEHP per void volume. This 'flush-evaporate' impregnation method allowed for loading a pre-determined amount of extractant and produces very small amounts of organic waste. An overview of the various impregnation approaches previously used for extractant coating on prepacked columns and bulk support materials is also presented.