SPECIATION OF SELENIUM ASSOCIATED WITH COAL-COMBUSTION BY-PRODUCTS USING HPLC-ICPMS
Separation of selenite and selenate is achieved within 2 minutes on a Brownlee C8 column using a 50µL injection loop and a flow rate of 1.0 mL/min at 25C. The mobile phase consists of an acetic acid-ammonium acetate buffer plus tetrabutylammonium hydroxide for the ion-pairing agent. The resulting pH is 5.4. At this pH, selenate is fully de-protonated (SeO4-2) but selenite is partially protonated (HSeO3-). This allows for separation by polarity, as well as size and weight. The addition of 5% methanol to the mobile phase acts as an organic modifier which creates cleaner peaks and shorter retention times. Variations of temperature, flow rates, methanol concentrations, pH, and mobile phase concentrations determine the optimal peak detections and retention times.
Separation was achieved for Se in spiked and un-spiked fly ash leachates. Initial results show that selenite is the dominant form of Se extracted from the fly ash with de-ionized water.