Cloud point microextraction involving graphene oxide for the speciation of very low amounts of chromium in waters

A graphene oxide (GO) suspension was used to retain chromium (III) species in a neutral solution. The addition of Triton X-45 followed by heating resulted in a coacervate, to which the GO nanoparticles containing the analyte retained were transferred. Chromium was determined directly in the surfactant-rich phase by electrothermal atomic absorption spectrometry. The procedure was repeated using a second aliquot of sample to which sodium hydrogen sulphite was added to reduce chromium (VI) to chromium (III). By again obtaining the analytical signal of chromium in the condensed phase, the concentration of the hexavalent form was calculated by difference. Using 10 mL for the sample volume and 0.01% for the Triton X-45 concentration, the enrichment factor was 140, and the detection limit was 5 ng L-1. The repeatability for five consecutive measurements at the 100 ng L-1 level was close to 5%. The reliability of the procedure was verified by analysing seven water samples with certified contents of total chromium. Speciation data are given for these standard materials and for seven potable waters and one seawater sample.