Parfait-distillation method

Combination Methods. Combination methods refer to those methods that employ both concentration and isolation methodologies. The modified parfait-distillation method that was evaluated used a series of adsorbents coupled with vacuum distillation to recover unadsorbed solutes (11). Porous polytetrafluoroethylene (PTFE) was used to adsorb the hydrophobic neutrals, and in field sampling it serves as a filter for particulate removal. Cation- and anion-exchange resins were then used to remove the ionized organic substances and to deionize the sample prior to the concentration of the nonadsorbed hydrophilic neutrals by vacuum distillation. Organic constituents were selectively... 

Recovery of Trace Organic Compounds by the Parfait-Distillation Method... 

The parfait-distillation method uses a sequential series of adsorbents to remove contaminants from water and vacuum distillation to recover unadsorbed materials. This method recovers a wide range of neutral, cationic, anionic, and hydrophobic contaminants. The first adsorbent, porous polytetrafluoroethylene (PTFE), removed humic acid and a broad range of hydrophobic compounds. PTFE was followed by Dowex MSC-1 and then Duolite A-162 ion-exchange resins. A synthetic hard water spiked parts-per-billion concentrations with 20 model compounds was used to evaluate the method. Poorly volatile, neutral, water-soluble species (glucose) cationic aromatics and most hydro-phobic compounds were recovered quantitatively. Model ampho-terics were removed from the influent but were not recovered from the adsorption beds. The recovery of model acids and bases ranged from 22% to 70% of the amount applied. 

The original parfait method rested on the use of vacuum distillation—lyophilization to concentrate the poorly volatile species in water. It might be expected that the removal of water under vacuum should be simple and straightforward. Vacuum distillation and lyophilization do indeed recover the poorly volatile contaminants from unfractionated surface waters. However, the compounds are often obtained in an intractable, insoluble form. These intractable precipitates are believed to form when bicarbonate dissociates under vacuum to form metal carbonate precipitates that trap organic polymers and lipids (4, 5). The parfait method prevents the formation of these precipitates by removing metal ions on an acidic cation-exchange bed. 

Losses during Vacuum Distillation and Lyophilization. The original parfait method used vacuum distillation to concentrate aqueous eluates from each of the parfait beds and the aqueous effluent... 

The original concept of the parfait method was to use vacuum distillation to concentrate the nonvolatile contaminants in water. The... 

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