Determination Of Cr Species Research Articles

Combination of dispersive solid phase extraction with dispersive liquid–liquid microextraction for the sequential speciation and preconcentration of Cr(III) and Cr(VI) in water samples prior to graphite furnace atomic absorption spectrometry determination

In this study, the combination of dispersive solid phase extraction (DSPE) with dispersive liquid–liquid microextraction (DLLME) was proposed as a novel sequential speciation method for Cr determination by graphite furnace atomic absorption spectrometry. In the first step, the selective extraction of Cr(III) by DSPE was achieved using graphene oxide (GO) nanoparticles as the adsorbent. The difficulty of separation and collection of GO in analytical performance was solved by the introduction of the syringe nanofilter. Then Cr(VI) was enriched by DLLME using [Omim] [PF6] as the extraction solvent. The experimental parameters affecting the performance of both preconcentration methods were investigated and optimized. Under the optimal conditions including the initial pH value of 7, 150μg GO, 2min ultrasound time, 210μL elution solvent (first step), secondary pH value of 4, 0.15% (m/v) Aliquat-336, 120μL of [Omim] [PF6] and 3min ultrasound time (second step), the linear range of 0.06–5ng/mL (R>0.997), the limits of detection of 0.015 and 0.02ng/mL were achieved for Cr(III) and Cr(VI), respectively. The relative standard deviations (n=5) of 0.6ng/mL Cr(III) and Cr(VI) were 3.2% and 4.6%, respectively. Finally, this newly developed method was applied for the speciation and determination of Cr species in different water samples and satisfactory results were obtained.

A critical overview of Cr speciation analysis based on high performance liquid chromatography and spectrometric techniques

The role and impact of chromium (Cr) on the environment and living organisms depends primarily on its chemical form. High toxicity of hexavalent Cr is well documented, while trivalent Cr is an essential micronutrient. In the last decades numerous analytical procedures have been developed for the determination of Cr(VI) in different sample matrices. To obtain reliable speciation data it is important to preserve species integrity during the sample storage, pre-treatment, extraction and the determination of Cr species. Among different speciation methods combination of high performance liquid chromatography (HPLC) with atomic spectrometry techniques provides comprehensive information on the presence of Cr species in a variety of sample matrices, while hyphenation of HPLC to inductively coupled plasma mass spectrometry (ICP-MS) represents the most powerful and the most sensitive analytical tool for Cr speciation. Precise isotope ratio measurement enables the application of isotope dilution techniques for the quantification of trace amounts of individual Cr species in various environmental and biological samples. Furthermore, enriched stable isotopes can be introduced as tracers to investigations on the fate and role of Cr in the environment and living organisms or to monitor the species transformation during the analytical procedure. Despite general understanding of Cr chemistry, which is closely related to its trivalent and hexavalent oxidation states and knowledge on conditions that may influence species transformation, there are still open questions that should be addressed to obtain reliable speciation analysis data. So, this article is focused mostly to overview recent developments in methodological approaches for Cr speciation in different sample matrices by applying HPLC and spectrometric techniques. Different procedures for preparation of isotopically enriched Cr spike solutions are critically evaluated. The advantages of their use as tracers to follow and account for species transformation during sample preparation and for the quantification of Cr species by HPLC-ID-ICP-MS are discussed. The importance of the use of adequate analytical methodologies and speciation analysis in the determination of Cr(VI) is highlighted in order to avoid inadequate conclusions to be made based on wrongly applied analytical methodologies. An increasing need to develop speciation procedures for selective determination of Cr(III) species is also emphasized.

Use of high surface area TiO2 for preconcentration and following determination of Cr species by on-line flow injection inductively coupled plasma atomic emission spectrometry

A flow-injection analysis (FIA) system incorporating two microcolumns of TiO 2 was used for the developing of an on- line method for preconcentration and sequential determination of Cr 3+ and Cr6+ species by inductively coupled plasma atomic emission spectrometry (ICP-AES). The optimal conditions for both analytes have been obtained. With a sample volume of 10-50 ml and an elution volume of 500 µl, a signal was 20-100 times higher than the signal given by a continuous aspiration system. The method gave good reproducibility with precisions less than 7 % RSD for 5 replicates at the 10 ng/ml level for both Cr- species. Recoveries between 95 and 98 % were obtained for Cr 3+ and Cr6+. The preconcentration system and the methodology proposed were validated on several natural water samples, on reference water samples as well as on synthetic seawater. It was found that the on-line detection using ICP-AES allows sequential Cr speciation analysis at the low concentration levels (ng/l) usually encountered in these media.