Preconcentrating Minicolumn Sensors for Trace Environmental Monitoring

Preconcentrating minicolumn sensors represent an effective approach to achieve a substantial preconcentration factor within a sensing device, enabling very low detection limits as is required for environmental sensing. A selectively sorbent phase collects and concentrates analyte molecules as sample liquid is pumped through the column, ultimately equilibrating the entire sorbent phase with the analyte concentration in the sample. At equilibration, the amount on the column will be proportional to the analyte concentration when working at trace concentrations. We have demonstrated radiometric detection for the detection of radionuclides with this sensor, incorporating scintillating material in the column with the sorbent phase. The pertechnetate form of 99-technetium can be sensed using a mixed column bed containing anion exchange resin and scintillating plastic beads, collecting scintillation light with a pair of photomultiplier (PMT) tubes external to the transparent column body. For hexavalent chromium, we can also collect anions with anion exchange resin. In this case, optical fibers are coupled to the column body to measure the optical absorbance as a function of the amount of hexavalent chromium captured by the column. Both sensors can detect their respective analytes to levels below water standards.