Ion-exchange-based eluent-free preconcentration of some anions.

Preconcentration procedures based on ion-exchange methods are often used to enhance the sensitivities of analytical techniques where the eluent used for eluting the preconcentrated ions does not influence the subsequent analytical step. Until recently, only a limited use of ion-exchange-based sample preconcentration procedures has been found in those analytical techniques where the eluent components strongly influence the separation procedure [e.g., capillary electrophoresis (CE)]. In this paper, we present a preconcentration procedure based on (i) the preconcentration of anions on an ion-exchange resin, (ii) the subsequent elution of analytes, and (iii) on-line removal of eluent components by chemical suppression using an appropriate suppressor device (either packed-bed suppressor column or micromembrane suppressor). The adjustment of the system parameters, combined with a computer-controlled, sensing/switching system, resulted in a minimal additional dilution of the eluted preconcentrated anions. The efficiency of the proposed enrichment/matrix removal procedure was tested by using off-line CE analysis of collected preconcentrated samples, reaching a LOD of 1 microg/l for a selected anion.