Electrodialytic ion isolation for matrix removal.

We report a fully automated online sample pretreatment system for ionic analytes that extracts the ionic analytes from the sample and largely removes the nonionic sample matrix and can preconcentrate the analyte. Sample pretreatment is a key analytical process; conventional pretreatment is conducted in a difficult to automate batchwise manner. The present system relies on the transport of ions induced by an electric field to a water acceptor. Cations and anions are simultaneously and separately collected into individual acceptor streams which can be directly introduced to a chemical analyzer. Common inorganic ions (≤10 meq/L) are quantitatively transferred from samples within a few seconds. Small nonionic molecules are transferred by 0.5-10%, and proteins are not transferred at all. The method has been successfully applied to drinking water, urine, and cow's milk with 3.7 ± 2.5, 3.8 ± 2.6, and 4.6 ± 2.6%, respectively, in variance (n = 10). Present results agreed well with those from conventional pretreatment methods. Interestingly, when calcium in milk is measured by the present method, the results correspond to the total calcium by conventional methods; i.e., it can extract calcium from its protein-bound form in milk.