On-site separation of Cr(vi) and Cr(iii) in natural waters by parallel cartridge ion-exchange columns

Abstract

A simple, fast, portable, and solvent-free method is developed for field separation of Cr(VI) and Cr(III) in natural waters. The method involves passing a water sample through parallel cation- and anion exchange resin cartridge columns at the field site. In a matter of seconds, all the Cr(III) is retained on the cation-exchange column and Cr(VI) passes to the effluent, while the Cr(VI) is quantitatively retained on the anion-exchange resin and Cr(III) passes to the effluent. The two collected solutions are preserved and determined later in the laboratory using inductively coupled plasma mass spectrometry (ICP-MS) or any other elemental analysis technique sufficiently sensitive to measure the Cr concentrations of interest. Cr(VI) (or Cr(III)) can be separated from Cr(III) (or Cr(VI)) at the pH range 1–10 at Cr(III)/Cr(VI) (or Cr(VI)/Cr(III)) concentration ratios as high as 10 000 (or 500). The limits of detection for Cr(III) and Cr(VI) are 0.03 and 0.01 μg L⁻¹, respectively. Repeatability expressed as relative standard deviation is determined to be 7.1% for Cr(VI) and 5.7% for Cr(III), using a drinking water sample containing 1.14 μg L⁻¹ Cr(VI) and 0.72 μg L⁻¹ Cr(III). The parallel cartridge ion-exchange resin columns can be used continuously for 40 drinking water samples without any regeneration or cleaning procedure. The accuracy is validated by analysing Cr(III) and Cr(VI) in three water standard reference materials (GBW080257, GBW080403, and GBW080404). Furthermore, the proposed method is applied to the on-site separation of Cr(III) and Cr(VI) from natural waters.