Microwave assisted extraction of Cr(iii) and Cr(vi) from soil/sediments combined with ion exchange separation and inductively coupled plasma optical emission spectrometry detection

Abstract

An analytical methodology has been developed for the speciation of Cr(III) and Cr(VI) in soil/sediments. The species of interest were extracted from samples using a solution containing 0.1 M EDTA, 1% tetrabutyl ammonium bromide (TBAB) and a little HF in a domestic microwave oven. The conditions for the quantitative extraction of the Cr species from sediments were optimized. The separation of anionic Cr(VI) from the sediment extract was carried out using the sulfate form of Dowex-1 at pH 4.5. Though the extract contained the anionic EDTA complex of Cr(III), it was quantitatively eluted. The adsorbed Cr(VI) was eluted with 2 M HNO₃. The determination of the separated Cr(VI) and Cr(III) in the effluent, and total Cr in the extract was carried out using ICP-OES. The recovery of the total Cr from the original samples was 96–99% and that of Cr(III) and Cr(VI) spiked was 97–102% with an RSD in the range of 5–6%. A developed methodology has been applied for the speciation of Cr in a certified reference material stream sediment (GBW-07312) and also four real world samples: two sediments collected from the Hussain Sagar lake, Hyderabad, India and two soils collected near the Uranium Corporation of India Limited (UCIL), Tummalapalli, Kadapa, India. The total concentration of Cr in the extract was in good agreement with the certified value of the stream sediment and with the complete dissolution method in case of the real world samples. The limit of detection of Cr(VI) was 0.02 mg L⁻¹, which corresponding to a detection limit of 5.0 mg kg⁻¹ for this method.