Chromium speciation by different methods of practical use for routine in situ measurement

Abstract
Simple, sensitive, low-cost, and relatively rapid methods for the detection of Cr (111) and Cr (VI) species in natural waters are needed for monitoring and regulatory purposes. Conventional acidification and storage of filtered samples can be a major cause of chromium losses from the `dissolved' phase. In situ monitoring is thus of paramount importance. The practical usefulness of selected chromium speciation methods was assessed in the laboratory and in the field. Significant discrepancies were found in the Cr (VI) detection efficiency by a selective ion meter based on the diphenylcarbazide method when compared with conventional Zeeman graphite fumace AAS. The efficiency of the DGT (Diffusion gradients in thin films) method, based on the deployment in situ of gel/resin units capable of separating labile species of Cr (III) and Cr (VI), looks promising, but is limited by cost considerations and by potential complications in the presence of complexing substances. The method based on the Sephadex DEAE A-25 ion exchange resins is quite effective in the separation of Cr species, though it requires on-site facilities, is relatively time-consuming and is potentially affected by complexing substances.