In-situ separation of chromium(III) and chromium(VI) and sequential ETV–ICP–AES determination using acetylacetone and PTFE as chemical modifiers

Electrothermal vaporization–inductively coupled plasma–atomic emission spectrometry (ETV–ICP– ES) has been used for the sequential determination of Cr(III) and Cr(VI). The method is based on the difference between the chelate reactions of the two Cr species and acetylacetone. Cr(III) chelate was separated from Cr(VI) and determined with use of acetylacetone as chemical modifier. The retained Cr(VI) in graphite tube was analyzed subsequently, after addition of polytetrafluoroethylene (PTFE) as chemical modifier. The different factors affecting the vaporization behavior of Cr(III) acetylacetonate were investigated in detail. The detection limits for Cr (III) and Cr(VI) were 0.56 and 1.4 ng mL^–1, respectively, and relative standard deviations for 0.1 μg mL^–1 Cr(III) and 0.1 μg mL^–1 Cr(VI) were 2.5% (n = 6) and 4.8% (n = 6), respectively. The linear ranges of the calibration curve for both Cr(III) and Cr(VI) covered three orders of magnitude. The proposed method was used to analyze water samples with satisfactory results.     

Speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A novel method for the speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-AES) was developed. The reaction conditions between Cr(III) and 8-hydroxyquinoline (8-Ox) and the vaporization behavior of the chelate formed were investigated in detail. It was found that the Cr(III)-8-Ox chelate could be formed at room temperature and vaporized from graphite furnace under controlled experimental conditions, therefore, an in situ separation of Cr(III) from Cr(VI) was achieved. The retained Cr(VI) in graphite tube was then determined by using fluorination vaporization ETV-ICP-AES with PTFE slurry as chemical modifier. Under optimum experimental conditions, the detection limits for Cr(III) and Cr(VI) are 8.6 ng/ml and 11.3 ng/ml, and the relative standard deviations (R.S.D.s) are 3.8% and 4.1% (c=0.1 μg/ml, n=6), respectively. The linear ranges of the calibration curve for both Cr(III) and Cr(VI) covered three orders of magnitude. The proposed method has been applied to the speciation of Cr(III) and Cr(VI) in water samples with the satisfactory results.     

Preparation of fluorescent polyvinyl alcohol keto-derivatives nanoparticles and selective determination of chromium(VI)

A novel fluorescent polyvinyl alcohol keto-derivatives nanoparticle (PVAK) has been prepared in one-step method. The nanoparticles has excitation and emission maxima at 349 and 462 nm, respectively. Based on the fluorescence quenching of PVAK by Cr(VI), we established a simple and selective fluorimetric method for the determination of Cr(VI) without separation of Cr(III) in water. The reaction conditions between Cr(VI) and PVAK were investigated in detail. Furthermore, the reaction mechanism between PVAK and Cr(VI) was also discussed. Under optimal experimental conditions, a limit of detection of 0.02 microg mL(-1) was achieved. The calibration curve was linear over the concentration range 0.1-13.2 microg mL(-1) with a correlation coefficient of 0.9987. The proposed method has been applied to the selective quantification of Cr(VI) in synthetic samples and waste-water samples with the satisfactory results.     

快速溶剂萃取-离子色谱法同时测定塑料中的三价铬和六价铬

建立了采用快速溶剂萃取-离子色谱同时测定塑料中三价铬和六价铬的方法。三价铬和六价铬分别以吡啶-2,6-二羧酸(PDCA)和1,5-二苯卡巴肼(DPC)作为络合剂在柱前和柱后进行衍生化,分别在紫外和可见波长下采用紫外检测器进行检测,灵敏度高,基体干扰小。本方法对三价铬和六价铬的检出限分别为5.0 μg/L和0.5 μg/L;分别在50～1000 μg/L和5.0～100 μg/L范围内呈现良好的线性关系,线性相关系数分别为0.9994和0.9998;三价铬和六价铬的回收率范围为90.7%～101.1%,相对标准偏差(RSD)为1.7%～4.4%。该方法分析速度快、灵敏度高、重现性好,可用于塑料中三价铬和六价铬的同时测定。     

Rapid spectrophotometric determination of chromium(III)

A spectrophotometric procedure is suggested for the determination of Cr(III). The reaction between Cr(III) and 2-(5-bromo-2-pyridylazo)-5-dimethylaminophenol is accelerated by sodium dodecyl sulphate(SDS), sodium benzoate causes a further increase in the absorbance of the chelate. The optimum pH range for the reaction is 5-5.8(benzoate buffer). The chelate exhibits maximum absorbance at 590 nm, obeys Beer's law over the concentration range 0.02-0.56 microg/ml of Cr(III), has molar absorptivity of 7.8 x 10(4) 1. mol(-1) cm(-1) and a Sandell sensitivity of 0.66 ng/cm. The metal to ligand ratio is 1:2 in the absence of SDS and 1:1 in its presence. A procedure for the determination of Cr(III) and Cr(VI), when present together, is described. The method has been applied to the analysis of Cr(III) in tap water.     

Chromium(III)-penicillamine complex: Some properties and rapid chelation from chromium(VI) and penicillamine

The complex formation of thiol chelators with Cr(III) and Cr(VI) was investigated by means of preparative, potentiometric pH, electronic and IR spectral measurements. Cr(III) formed a 1:2 monomeric chelate with penicillamine (distorted octahedral mercapto-amino-carboxyl coordination) and a 1:3 monomeric chelate with thiolactic acid (regular octahedral mercapto-carboxyl coordination). The stepwise stability constants were estimated as log K₁ = 15.97 and log K₂ = 12.42 for the penicillamine chelate and as log K₁ = 13.39, log K₂ = 9.27 and log K₃ = 7.12 for the thiolactic acid chelate. The order of coordinating ability of donor groups to Cr(III) was mercapto ⪢ amino > carboxyl groups. The 1:2 Cr(III)-penicillamine chelate was very rapidly obtained by the reaction of Cr(VI) with penicillamine. The metal-ligand ratio required was 1:3 for the completion of this reductive chelation of Cr(VI) penicillamine. The rate law was found to be rate = k[Cr(VI][penicillamine] where k is 5.49±0.46 × 10⁻¹ M⁻¹ sec⁻¹ at pH 7.0. The mechanism for the reductive chelation was presumed to be: (i) reduction of Cr(VI) to Cr(V) by penicillamine, (ii) coordination of penicillamine to Cr(V) and then (iii) reduction of the Cr(V) chelate to inert Cr(III) chelate. These results are discussed in relation to be biological essentiality of Cr(III), the toxicity of Cr(VI) and the detoxication mechanism of “antichrome” agents.     

Selective fluorescence determination of chromium (VI) in water samples with terbium composite nanoparticles

The strong fluorescence Tb/acetyl acetone (acac)/Poly (Acrylamide) (PAM) composite nanoparticles have been prepared under ultrasonic radiation. The nanoparticles were water-soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. Based on the fluorescence quenching of Tb/acac/PAM by Cr (VI), a method for the selective determination of Cr (VI), without separation of Cr (III) in water, was developed. The reaction condition between Cr (VI) and Tb/acac/PAM were investigated in detail. Under optimal experimental conditions, the linear calibration curve was obtained over the concentration range of 5-600 ng mL(-1) with a correlation coefficient of 0.9939. The corresponding detection limit is 0.8 ng mL(-1) and the relative standard deviation is 1.5% for 0.05 microg mL(-1) (n=7). The proposed method has been applied to the selective quantification of Cr (VI) in synthetic samples and waste-water samples with the satisfactory results. The assay is characterized by short reaction time, very few interference, stable fluorescence signals, simple instrument and simplicity.     

Sequential injection wetting film extraction applied to the spectrophotometric determination of chromium(VI) and chromium(III) in water

The spectrophotometric determination of Cr(VI) and Cr(III) via sequential injection was used to demonstrate the sensitivity enhancement provided by a newly developed wetting film extraction system. The reaction product of Cr(VI) with 1,5-diphenylcarbazide was ion-paired with perchlorate and extracted into an organic wetting film consisting of octanol and 4-methyl-2-pentanone on the inner wall of a Teflon tube. The wetting film, with the extracted analyte, was then eluted with 100 mul acetonitrile and the analyte determined spectrophotometrically at 546 nm. Important optimized parameters were the selection of wetting film and elution solvents, the flow rate, the length and diameter of the extraction coil and the conditions for the formation of the ion paired chelate. Cr(III) was previously oxidized to Cr(VI) and calculated as the difference between total Cr and Cr(VI). An enrichment factor of 25 and a detection limit of 2.0 mug l(-1) Cr(VI) were achieved with a sampling frequency of 17 h(-1). The calibration curve was linear up to 100 mug l(-1) Cr(VI) (r = 0.999). The relative standard deviations were 2.8 and 2.0% at the 25 and 100 mug l(-1) levels.     

Short-column CE coupled with inductively coupled plasma MS for high-throughput speciation analysis of chromium

A method was developed for high-throughput speciation analysis of chromium by on-line coupling of short-column capillary electrophoresis (SC-CE) and inductively coupled plasma mass spectrometry (ICP-MS). Baseline separation of Cr(III) and Cr(VI) was achieved within 1 min by SC-CE in a 15 cm x 75 microm id fused-silica capillary at 6 kV using 15 mM HNO(3) as running electrolyte. The precisions (RSD, n = 5) of migration time and peak area for Cr(III) and Cr(VI) were in the range of 1.8-2.4% and 2.2-5.7%, respectively. The limits of detection (3sigma) of Cr(III) and Cr(VI) were 1.8 and 1.9 microg/L, respectively. The synthesized samples containing Cr(III) and Cr(VI) species were determined by the developed SC-CE-ICP-MS hyphenated technique, and the recoveries of Cr(III) and Cr(VI) in the synthesized samples were in the range of 103-110% and 90-108%, respectively.     

Chromium(III)-imprinted silica gel for speciation analysis of chromium in environmental water samples with ICP-MS detection

A new chromium(III)-imprinted 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS)-functionalized silica gel sorbent was synthesized by a surface imprinting technique and was employed as a selective solid-phase extraction material for speciation analysis of chromium in environmental water samples prior to its determination by inductively coupled plasma mass spectrometry (ICP-MS). The prepared Cr(III)-imprinted silica gel shows the selectivity coefficient of more than 700 for Cr(III) in the presence of Mn(II). The static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Cr(III) were 30.5 mg g(-1) and 13.4 mg g(-1). It was also found that Cr(VI) could be adsorbed at low pH by the prepared imprinted silica gel, and this finding makes it feasible to enrich and determine Cr(VI) at low pH without adding reducing reagents. The imprinted silica gel sorbent offered a fast kinetics for the adsorption and desorption of both chromium species. Under the optimized conditions, the detection limits of 4.43 pg mL(-1) and 8.30 pg mL(-1) with the relative standard deviations (R.S.D.s) of 4.44% and 4.41% (C=0.5 ng mL(-1), n=7) for Cr(III) and Cr(VI) were obtained, respectively. The proposed method was successfully applied to the speciation of trace chromium in environmental water samples. To validate the proposed method, two certified reference materials were analyzed and the determined values were in a good agreement with the certified values. The developed method is rapid, selective, sensitive and applicable for the speciation of trace chromium in environmental water samples.     

Preconcentration of chromium(III) and speciation of chromium by electrothermal atomic absorption spectrometry using cellulose adsorbent

A simple and sensitive method has been developed for species selective determination of chromium(III) and chromium(VI) in water by electrothermal atomic absorption spectrometry. The procedure is based on selective absorption of Cr(III) on a cellulose micro column (pH 11, 0.5 mol L(-1) NaCl). Total chromium was subsequently determined after appropriate reduction of Cr(VI) to Cr(III). Recoveries of more than 97% were found. A concentration factor of 100 was achieved. The relative standard deviations (n=10) at the 40 ng L(-1) level for chromium(III) and chromium(VI) were 2.3% and 1.8% and corresponding limits of detection (based on 36) were 1.8 ng L(-1) and 5.1 ng L(-1), respectively. No interference effects have been observed from other investigated species and the method has been successfully applied to natural water samples.     

Selective fluorescence determination of chromium(VI) with poly-4-vinylaninline nanoparticles

The strong fluorescence poly-4-vinylaniline nanoparticles (PVN) has been prepared under ultrasonic radiation. Based on the fluorescence quenching of PVN by Cr(VI), a method for the selective determination of Cr(VI), without separation of Cr(III) in water, was developed. The reaction conditions between Cr(VI) and PVN were investigated in detail. The assay is characterized by short reaction time (<1 min even at 0 degrees C temperature), very few interference stable fluorescence signals (at least 2.5 h), simple instrument (common spectrofluorometer) and simplicity (a one-step assay). Under optimal experimental conditions, a limit of detection of 0.02 microg ml(-1) was achieved. The calibration curve was linear over the concentration range 0.1-13.0 microg ml(-1) with a correlation coefficient of 0.9984. The proposed method has been applied to the selective quantification of Cr(VI) in synthetic samples and waste-water samples with the satisfactory results.     

Luminescent and magnetic Fe3O4/Py/PAM nanocomposites for the chromium(VI) determination

A novel luminescent and magnetic Fe(3)O(4)/pyrene/polyacrylamide (Fe(3)O(4)/Py/PAM) nanocomposite has been prepared under ultrasonic radiation. This magnetic nanocomposite combined with pyrene would lead to a special functional magnetic luminescent composite that enjoys both the advantages of magnetic nanoparticles of Fe(3)O(4) and fluorescence nanoparticles of pyrene. Taking advantage of the magnetic property of Fe(3)O(4) nanocomposites, we can separate Fe(3)O(4)/Py/PAM nanocomposites from solution easily just by using a permanent magnet. Based on the fluorescence quenching of Fe(3)O(4)/Py/PAM nanocomposites by Cr(VI), a method for the selective determination of Cr(VI), without separation of Cr(III) in water, was developed. Under optimal experimental conditions, a limit of detection of 0.01 microg mL(-1) was achieved. The calibration curve was linear over the concentration range of 0.1-14.0 microg mL(-1) with a correlation coefficient of 0.9975. The proposed method has been applied to the selective quantification of Cr(VI) in synthetic samples and wastewater samples with the satisfactory results.     

Separation of chromium(III) and chromium(VI) by ion chromatography and an inductively coupled plasma mass spectrometer as element-selective detector

Due to its extensive use in industrial processes, large quantities of chromium compounds are discharged into the environment. Common approaches for the speciation of Cr employ the determination of Cr(VI) and total Cr. The focus of the present work was a separation of Cr(III) and Cr(VI) species, with a minimum of sample preparation, by keeping an eye on the more relevant and toxic Cr(VI). For the successful simultaneous separation of both chromium species we implemented a RSpak NN-814 4DP (PEEK, 4 mm x 150 mm) multi-mode column using an eluent containing 90 mM ammonium sulfate and 10 mM ammonium nitrate, adjusted to pH 3.5. At a flow of 0.3 mL min(-1) the separation of both Cr species was possible within 8 min. Further the octopole reaction system of the inductively coupled plasma mass spectrometer was systematically studied and optimised to reduce the influence of polyatomic interferences. The major advantage of the developed method compared to published methods is that a derivatisation of the Cr(III) species--an invasion in the speciation--is not required. With the used multi-mode column both chromium species are retained. Furthermore the pH of the mobile phase (pH 3.5) prevents reduction of Cr(VI) as well as precipitation of Cr(III) during the analysis. A limit of determination of approximately 0.5 microg L(-1) for both chromium species with an injection volume of 25 microL was obtained. The optimised method was successfully applied to the determination of Cr(VI) in cement samples as well as chromium speciation analysis in homeopathic drugs.     

Cloud point extraction for high-performance liquid chromatographic speciation of Cr(III) and Cr(VI) in aqueous solutions

Cloud point extraction (CPE) was applied as a preconcentration step for HPLC speciation of chromium in aqueous solutions. Simultaneous preconcentration of Cr(III) and Cr(VI) in aqueous solutions was achieved by CPE with diethyldithiocarbamate (DDTC) as the chelating agent and Triton X-114 as the extractant. Baseline separation of the DDTC chelates of Cr(III) and Cr(VI) was realized on a RP-C18 column with the use of a mixture of methanol-water-acetonitrile (65:21:14, v/v) buffered with 0.05 M NaAc-HAc solution (pH 3.6) as the mobile phase at a flow rate of 1.0 ml min(-1). The precision (R.S.D.) for eight replicate injections of a mixture of 100 microg l(-1) of Cr(III) and Cr(VI) were 0.6 and 0.5% for the retention time, 4.1 and 4.6% for the peak area measurement, respectively. The concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for HPLC separation and in the initial solution, was 65 for Cr(III) and 19 for Cr(VI). The linear concentration range was from 50 to 1000 microg l(-1) for Cr(III) and 50-2000 microg l(-1) for Cr(VI). The detection limits of Cr(III) and Cr(VI) were 3.4 and 5.2 microg l(-1), respectively. The developed method was applied to the speciation of Cr(III) and Cr(VI) in snow water, river water, seawater and wastewater samples.     

Separation and preconcentration of chromium species by selective absorption on Lemna minor and determination by slurry atomisation electrothermal atomic absorption spectrometry

A novel method for the separation and preconcentration of Cr(III)/Cr(VI) with Lemna minor and determination by slurry atomization electrothermal atomic absorption spectrometry (ETAAS) was developed. A sample solution was added to a polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 1.0, stirred for 8 min for selective absorption of Cr(III) and then centrifuged. The upper layer of solution was transferred into another polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 5.0, stirred for 12 min for adsorption of the residual Cr(VI) and centrifuged. The two residues in two centrifuge tubes were washed twice with water, 2 ml of agar solution added, stirred for 2 min, then two slurries were prepared and used for the determination of Cr(III) and Cr(VI) by ETAAS. Detection limits (3sigma) of 0.01 microg L(-1) for Cr(III) and 0.03 microg L(-1) for Cr(VI) were obtained. The relative standard deviation was 2.8% for Cr(III) and 3.3% for Cr(VI) at the 1 microg L(-1) level. The method was applied to the determination of Cr(III)/Cr(VI) in water samples. The analytical recoveries of Cr(III) and Cr(VI) added to samples were 97-102 and 96-103%, respectively.     

Sequential injection analysis for Cr(VI) and Cr(III) with renewable surface reflection spectrophotometry.

On the basis of the chromogenic reaction of chromium(VI) with 1,5-diphenylcarbohydrazide (DPC) on the surface of Polysorb C-18 beads and the sequential injection renewable surface technique (SI-RST), a highly sensitive reflect spectrophotometric method for the determination of chromium(III) and chromium(VI) was proposed. Considerations of system and flow cell design, and factors that influence the determination performance were discussed. With 300 microl of sample loaded and 0.6 mg of beads trapped, the linear response range was 0.02 - 0.5 mg l(-1) Cr(VI) with a detection limit (3 sigma) of 2.4 microg l(-1) Cr(VI). The method achieves a precision of 1.3% RSD (n = 11) and a throughput of 53 samples per hour. The determination of Cr(III) was based on the same reaction for the determination of Cr(VI) after being oxidized by (NH4)2S2O8. The precision of the oxidation method was evaluated using a 0.2 mg l(-1) Cr(III) standard, yielding an RSD of 2.5% (n = 11). The average recovery of Cr(III) oxidized was tested to be 99.1%. The proposed method was used in the simultaneous determination of Cr(VI) and Cr(III) in water samples, and the error was less than 3%.     

Speciation of chromium by selective separation and preconcentration of Cr(III) on an immobilized nanometer titanium dioxide microcolumn

Nanometer titanium dioxide immobilized on silica gel (immobilized nanometer-scale TiO2 particles) was prepared by a sol-gel method and characterized by X-ray diffraction and scanning electron microscopy. The adsorptive behavior of Cr(III) and Cr(VI) on immobilized nanometer TiO2 was assessed. Cr(III) was selectively sorbed on immobilized nanometer TiO2 in the pH range of 7-9, while Cr(VI) was found to remain in solution. A sensitive and selective method has been developed for the speciation of chromium in water samples using an immobilized nanometer TiO2 microcolumn and inductively coupled plasma atomic emission spectrometry. Under optimized conditions (pH 7.0, flow rate 2.0 mL/min), Cr(III) was retained on the column, then eluted with 0.5 mol/L HNO3 and determined by ICP-AES. Total chromium was determined after the reduction of Cr(VI) to Cr(III) by ascorbic acid. The adsorption capacity of immobilized nanometer TiO2 for Cr(III) was found to be 7.04 mg/g. The detection limit for Cr(III) was 0.22 ng/mL and the RSD was 3.5% (n = 11, c = 100 ng/ mL) with an enrichment factor of 50. The proposed method has been applied to the speciation of chromium in water samples with satisfactory results.     

Preconcentration and separation of Cr(III) and Cr(VI) using sawdust as a sorbent

A simple, inexpensive method based on solid-phase extraction (SPE) on sawdust from Cedrus deodera has been developed for speciation of Cr(III) and Cr(VI) in environmental water samples. Because different exchange capacities were observed for the two forms of chromium at different pH—Cr(III) was selectively retained at pH 3 to 4 whereas Cr(VI) was retained at pH 1—complete separation of the two forms of chromium is possible. Retained species were eluted with 2.5 mL 0.1 mol L⁻¹ HCl and 0.1 mol L⁻¹ NaOH. Detection limits of 0.05 and 0.04 μg mL⁻¹ were achieved for Cr(III) and Cr(VI), respectively, with enrichment factors of 100 and 80. Recovery was quantitative using 250 mL sample volume for Cr(III) and 200 mL for Cr(VI). Different kinetic and thermodynamic properties that affect sorption of the chromium species on the sawdust were also determined. Metal ion concentration was measured as the Cr(VI)–diphenylcarbazide complex by UV–visible spectroscopy. The method was successfully applied for speciation of chromium in environmental and industrial water samples.     

The use of 1-phenyl-3-methyl-4-benzoyl-5-pyrazone as chemical modifier for low-temperature electrothermal vaporization for separation and determination of Cr(III) and Cr(VI) by ICP-MS

Based on thermal stability and volatility of 1-phenyl-3-methyl-4-benzoyl-5-pyrazone (PMBP) chelate, a novel method was described for the determination of Cr(III) and Cr(VI) by low-temperature electrothermal vaporization (LETV) combined with inductively coupled plasma mass spectrometry (ICP-MS). It was found that Cr(III) could be rapidly formed in a graphite furnace, and quantitatively vaporized into ICP at a relatively low temperature of 1000 °C with the use of PMBP as a chemical modifier, while Cr(VI) was retained in the graphite tube. Thus, the separation of Cr(III) and Cr(VI) could be realized. The main factors affecting the formation and vaporization of Cr(III)-PMBP chelate were investigated in detail. Under the optimized conditions, the detection limit of Cr(III) for this method was 0.031 ng mL⁻¹ and the relative standard deviation (RSD) for 1.0 ng mL⁻¹ Cr(III) was 5.3% (n = 9, v = 10 μL). The linear range of calibration curve spanned three orders of magnitude. The proposed method was applied to the determination of Cr(III) and Cr(VI) in water samples with satisfactory results.