Determination Of Chromium In Seawater Research Articles

Solid phase microextraction for the determination of chromium in sea-water

Application of solid phase microextraction (SPME) to the extraction of Cr from sea-water after derivatization with the β-diketonate ligand 1,1,1-trifluoro-2,4-pentadione (trifluoroacetylacetone) is reported. The chelation reaction was conducted in a single (aqueous) phase medium. Both liquid phase and headspace extraction were studied by employing a 100 µm PDMS (polydimethylsiloxane) coated SPME fiber. Capillary gas chromatography (GC) coupled to electron capture detection (ECD), electron impact-mass spectrometry (EI-MS) and inductively coupled plasma-mass spectrometry (ICP-MS) were compared for the quantitation of Cr. Except for the ECD, isotope dilution calibration was applied, using 53Cr enriched spikes. Detection limits between 0.011–0.015 ng ml−1 (as Cr) were achieved with all three systems. Accuracy was assessed using CASS-4 Nearshore Seawater Certified Reference Material (CRM) from the National Research Council of Canada (NRCC). The developed method provided accurate results with EI-MS and ICP-MS detection, while significant bias was experienced with the ECD.

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.

Direct determination of chromium in estuarine and coastal waters by electrothermal atomic absorption spectrometry

The determination of chromium in sea-water by electrothermal atomic absorption spectrometry suffers from large variations in sensitivity that are a function of the salinity, the batch and age of the graphite tube, and the analytical instrument used. To avoid the need for lengthy standard additions calibration, work was undertaken to discover a chemical modifier permitting direct analysis over a range of salinities. Two such modifiers were identified as suitable for use in the determination of total dissolved chromium. Magnesium nitrate (100 µg) gave good recoveries (with respect to de-ionized water) for low to medium salinities, with a limit of detection of 0.05 µg l–1. At high salinities however (about 34 parts per thousand), about 15% suppression was measured, making the method unsuitable for sea-water samples. Sodium tungstate (2.5 µg) although slightly less sensitive (detection limit of 0.1 µg l–1), produced excellent recoveries over all salinities. Thus the method allows the direct determination of dissolved chromium in estuarine and polluted coastal waters.

Determination of chromium in seawater by isotope dilution gas chromatography/mass spectrometry

Determination of chromium in seawater by isotope dilution gas chromatography/mass spectrometry