Analysis and storage of samples for chromium determination in seawater

An improved method for determination of chromium in seawater has been developed. The procedure is based on the ion-pair extraction of Cr(VI) with tricaprylmethyl ammonium chloride (Aliquat-336) into methyl isobutyl ketone (MIBK). The extract is analyzed by Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS). The possibility to determine total chromium by oxidation of Cr(III) is also shown. Different ways for storage of natural seawater samples in order to avoid speciation changes were also investigated. Coastal seawater could be stored at least one month at natural pH and at room temperature. Cr(VI) in frozen oceanic water is stable for at least eight months. The method allows rapid determination of Cr(VI). Measurements on CASS-2 reference material gave a Cr(VI) concentration of 2.76 ± 0.09 nM (n = 6), compared to the certificated value 2.32 ± 0.40 nM. The detection limit based on 3σ of the blank is 0.1 nM. The determination of total chromium is more time-consuming and has a slightly lower precision.