Determination of hexavalent chromium concentration in industrial waste incinerator stack gas by using a modified ion chromatography with post-column derivatization method

- A conventional IC-DPC method was modified to detect trace-level hexavalent chromium.
- Gradient elution was superior to isocratic elution to resolve the Cr(VI) ion peak.
- Cr(VI) concentration in stack gas of 8 industrial waste incinerators was determined.
- Cr(VI) concentration in stack gas ranged from below the MQL to 3100 ng/m3.
- Cr(VI) concentration was 2-3 orders of magnitude higher in stack gas than in air.

An ion chromatography with post-column derivatization with 1,5-diphenylcarbazide (IC-DPC) analytical method was modified to enable measurement of trace-level hexavalent chromium (Cr(VI)) in air. One of the difficulties in determining trace levels of Cr(VI) in air with conventional IC-DPC methods is co-elution of the solvent and ion peaks due to high concentrations of ionic compounds in the extract. However, by using gradient elution rather than isocratic elution we were able to fully resolve the Cr(VI) ion peak from the solvent peak without the need for diluting the extract, which would have reduced the minimum quantifiable level of the method. With this method, we were able to detect Cr(VI) in air at concentrations of 5.3 ng/m3 (assuming a sampling volume of 1 m3 and a final solution volume of 10 mL). Recovery tests at three different concentrations of Cr(VI) (50, 250, 1000 ng) were performed with or without fly ash; recovery rates at all the concentrations of Cr(VI), with or without fly ash, ranged from 68% to 110% (mean ± relative standard deviation, 96% ± 11%), and there were no differences in recovery rates with respect to the presence or absence of fly ash. Finally, we used the developed method to determine the concentration of Cr(VI) in stack gases collected from eight industrial waste incinerators located in Japan. The concentration of Cr(VI) in the stack gases ranged from below the method quantification limit to 3100 ng/m3. The highest concentrations of Cr(VI) detected in the stack gases were two to three orders of magnitude higher than that in ambient air in Japan.