Speciation Of Chromium Species Research Articles

Nickel oxide/nickel ferrite/layered double hydroxide nanocomposite as a novel magnetic adsorbent for chromium speciation

A facile hydrothermal method was used to prepare a magnetic nanocomposite (MNC) based on nickel oxide/nickel ferrite/Ni-Al layered double hydroxide (NiO/NiFe2O4/LDH). The synthesized NiO/NiFe2O4/LDH MNC was characterized using various techniques, including X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and vibrating sample magnetometry. After evaluation of its capability to selective extraction of Cr(VI) ions, an efficient magnetic solid-phase extraction method was developed for the pre-concentration and speciation of chromium species (Cr(III) and Cr(VI)) using the as-prepared NiO/NiFe2O4/LDH MNC as an adsorbent and flame atomic absorption spectrometry. Due to owning positively charged surface, the LDH can establish selective electrostatic interaction with Cr(VI) species in the form of CrO42- or HCrO4-. Numerous important parameters influencing the extraction efficiency were studied and optimized. Based on the method validation applying the optimized extraction conditions, the calibration curve was linear in the range of 0.5 to 120 ng mL−1 with a correlation coefficient of 0.9983. The limit of detection was estimated to be 0.14 ng mL−1, and the method intera- and inter-day precisions were 1.47% and 3.19%, respectively. The presented method was validated by the analysis of the certified reference material NIST SRM 1643e, and applied for the speciation of Cr(VI) and Cr(III) species in various water and industrial wastewater samples.

Preconcentration and speciation of chromium species using ICP-OES after ultrasound-assisted magnetic solid phase extraction with an amino-modified magnetic nanocomposite prepared from Fe3O4, MnO2 and Al2O3

The article describes a method for preconcentration and speciation of Cr(III) and Cr(VI) in river waters. It is based on ultrasound-assisted magnetic solid phase extraction employing a nanocomposite prepared from magnetite nanoparticles, manganese oxide and alumina oxide, and then functionalized with [3-(2-aminoethylamino)propyl] trimethoxysilane (AAPTMS). By taking advantage of the oxidative properties of MnO2, the Fe3O4@MnO2,Al2O3 nanocomposite was used for the preconcentration of total chromium. The AAPTMS-modified nanocomposite, in turn, is selective for Cr(VI). The concentration of Cr(III) can be calculated as the difference between total chromium and Cr(VI). The preconcentrated chromium species were quantified using ICP-OES. The method was optimized using response surface methodology. Under optimal conditions, the limit of detection and quantification are 20 and 50 pg ⋅ mL−1, respectively. The intraday and interday precisions of the method, expressed in terms of relative standard deviation, are 2.6 and 4.9%, respectively. In addition, the effects of potentially interfering ions were examined. The method was successfully applied to the speciation of chromium in spiked river water and a certified reference material.

Speciation of chromium through aqueous two-phase extraction of complexes of Cr(III) with 4-(2-pyridylazo)resorcinol and Cr(VI) with 1,5-diphenylcarbazide

A green, sensitive and selective methods are described for the preconcentration and speciation of chromium species in natural waters. The developed methods are based on the environmentally friendly aqueous two-phase extraction with a system consisted of ammonium sulfate and polyethylene glycol, or, alternatively, alcohol (ethanol, isopropanol). The extraction of chromium species from aqueous solution into the upper organic phase was performed with 4-(2-pyridylazo)resorcinol and 1,5-diphenylcarbazide as chelating agents for Cr(III) and Cr(VI), respectively. Some predominant factors affecting the preconcentration and speciation of both Cr(III) and Cr(VI) species were evaluated and optimized. The concentration of chromium species in upper organic phase was determined by both spectrophotometric and electrothermal atomic-absorption spectrometry (ET AAS) methods. Under the optimum conditions, the calibration graphs obtained with spectrophotometric method were linear over the concentration ranges from 5 to 500 ?g L-1 for Cr(III) and from 2.5 to 50 ?g L-1 for Cr(VI). Corresponding concentration ranges determined by using ET AAS method were from 1 to 10 ?g L-1 for both chromium species. The proposed methods were applied to the determination of chromium species in mine and waste waters with satisfactory results.

A new chelating resin: Synthesis, characterization and application for speciation of chromium (III)/(VI) species

A new method for speciation, preconcentration and separation of Cr(III) and Cr(VI) in different matrices was developed using solid phase extraction and flame atomic absorption spectrometry (FAAS). Poly-2-(5-methylisoxazole) methacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid-co-divinylbenzene) (MAD), was synthesized and characterized as a new chelating resin for the speciation of Cr(III)/Cr(VI) species. Cr(III) was quantitatively recovered on chelating resin at pH range of 1.5–4.5, while Cr(VI) was not quantitatively recovered in all the pH's. The optimum conditions for the speciation of Cr(III)/Cr(VI) species were investigated on several commonly tested experimental parameters such as pH of the solution, amount of the resin, sample volume, and interfering ions. The preconcentration factor was found to be 200. The limit of detection for Cr(III) corresponding to three times the standard deviation of the blank (3s) was found 0.01μgL−1. Adsorption capacity and binding equilibrium constant were calculated to be 34.3mgg−1 and 1.5Lmg−1, respectively. The method was validated by analysing certified reference materials. The proposed method was applied to the determination and speciation of chromium species in various water and food samples with satisfactory results.

Hydrogels as a Potential Chromatographic System: Absorption, Speciation, and Separation of Chromium Species from Aqueous Media

Hydrogels with highly charged forms and amphiphilic character, based on an anionic monomer 2-acrylamido-2-methyl-1-propansulfonic acid sodium salt (AMPSNa) and a cationic monomer 3-acrylamidopropyltrimethylammoniumchloride (APTMACl), were synthesized via a photo-polymerization technique and investigated for potential use in the separation of chromium species with different oxidation states. They were used for three main purposes. First, a single chromium species was successfully removed from an aqueous medium in the presence of other forms using the appropriate design and synthesis of the hydrogels. Secondly, the copolymerized p(AMPSNa-co-APTMACl) hydrogels were used to remove two chromium species simultaneously from an aqueous medium. Lastly, in addition to speciation of the chromium species, their separation and removal by an externally applied magnetic field using magnetically responsive hydrogels was demonstrated.

Tea-industry waste activated carbon, as a novel adsorbent, for separation, preconcentration and speciation of chromium

Activated carbon was produced from tea-industry wastes (TIWAC) and employed as a low cost and effective solid phase material for the separation, preconcentration and speciation of chromium species without using a complexing agent, prior to determination by flame atomic absorption spectrometry (FAAS). The characterization of TIWAC was performed by utilizing several techniques such as Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), and elemental analysis. The adsorption experiments were conducted in a batch adsorption technique. Under the experimental conditions, Cr(VI) adsorption amount was nearly equal to zero, however the adsorption percentage of Cr(III) was in the range of 95–100%. Therefore total chromium was determined after the reduction of Cr(VI) to Cr(III) and Cr(VI) was calculated by subtracting Cr(III) concentration from total chromium concentration. The suitable conditions for adsorption and speciation processes were evaluated in terms of pH, eluent type and volume, TIWAC concentration, adsorption and desorption contact time, etc. Adsorption capacity of TIWAC was found to be 61.0 mg g −1. The detection limit for Cr(III) was found to be 0.27 μg L −1 and the preconcentration factor was 50 for 200 mL of sample volume. The procedure was applied to the determination and speciation of chromium in stream, tap and sea water. Also, the proposed method was applied to total chromium preconcentration in microwave digested tobacco and dried eggplant samples with satisfactory results. The method was validated by analyzing certified reference materials (CRM-TMDW-500 Drinking Water and CRM-SA-C Sandy Soil C) and the results were in good agreement with the certified values.

Determination of adsorption and speciation of chromium species by saltbush ( Atriplex canescens) biomass using a combination of XAS and ICP–OES

Studies were performed to determine the effect of pH on chromium (Cr) binding by native, esterified, and hydrolyzed saltbush ( Atriplex canescens) biomass. In addition, X-ray absorption spectroscopy studies were performed to determine the oxidation state of Cr atoms bound to the biomass. The amounts of Cr adsorbed by saltbush biomass were determined by inductively coupled plasma–optical emission spectroscopy (ICP–OES). For Cr(III), the results showed that the percentages bound by native stems, leaves, and flowers at pH 4.0 were 98%, 97%, and 91%, respectively. On the other hand, the Cr(VI) binding by the three tissues of the native and hydrolyzed saltbush biomass decreased as pH increased. At pH 2.0 the stems, leaves, and flowers of native biomass bound 31%, 49%, and 46%, of Cr(VI), respectively. The results of the XAS experiments showed that Cr(VI) was reduced in some extend to Cr(III) by saltbush biomass at both pH 2.0 and pH 5.0. The XANES analysis of the Cr(III) reaction with the saltbush biomass parts showed an octahedral arrangement of oxygen atoms around the central Cr(III) atom. The EXAFS studies of saltbush plant samples confirmed these results.