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.     

Separation and preconcentration of Se(IV)/Se(VI) speciation on algae and determination by graphite furnace atomic absorption spectrometry in sediment and water

A novel method for the separation and preconcentration of Se(IV)/ Se(VI) with algae and determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. The Se(VI) is extracted with algae from the solution containing Se(IV)/Se(VI) at pH 5.0, and the remaining Se(IV) is then preconcentrated pH 1.0. The detection limits (3σ, n = 11) of 0.16 μg L^–1 for Se(IV) and 0.14 μg L^–1 for Se(VI) are obtained using 40 mL of solution. At the 2.0 μg L^–1 level the relative standard deviation is 2.6% for Se(IV) and 2.3% for Se(VI). The method has been applied to the determination of Se(IV)/Se(VI) in sediment and water samples. Analytical recoveries of Se(IV) and Se(VI) added to samples are ?97 ± 5% and 102 ± 6% (95% confidence), respectively. Received: 10 February 1999 / Revised: 21 June 1999 / /Accepted: 22 June 1999     

Speciation of chromium in water using crosslinked chitosan-bound FeC nanoparticles as solid-phase extractant, and determination by flame atomic absorption spectrometry

Crosslinked chitosan-bound FeC nanoparticles (CCBFeCNP) were prepared, and the adsorptive behavior of Cr(III) and Cr(VI) on CCBFeCNP were assessed. At pH 6.0–10.0, CCBFeCNP is selective towards Cr(III) but hardly selective towards Cr(VI). The retained Cr(III) is subsequently eluted with 0.5 mol L⁻¹ HCl. Total chromium is determined after reduction of Cr(VI) to Cr(III) by ascorbic acid. A new method of flow injection using a micro-column packed with CCBFeCNP as solid phase extractant has been developed for speciation of Cr(III) and Cr(VI) in water samples, followed by flame atomic absorption spectrometry. The effects of pH, sample flow rate and volume, elution solution and interfering ions on the recoveries of Cr(III) were systematically investigated. Under optimum conditions, the adsorption capacity of CCBFeCNP for Cr(III) is 10.5 mg g⁻¹ at pH 7.5. The procedure presented was applied to chromium speciation in water samples, and the results were satisfactory.     

Flavonol Derivatives for Determination of Cr(III) and W(VI)

 Simple, rapid, sensitive and selective methods for the determination of Cr(III) and W(VI) with flavonol derivatives in the presence of surface-active agents are proposed. In the pH ranges 3.4–4.2 and 1.9–2.5, the molar absorptivities of Cr(III)-morin-emulsifier S (EFA) and W(VI)-morin-polyvinylpyrrolidone (PVP) systems are 1.13×10⁵ and 2.13×10⁴ L mol⁻¹ cm⁻¹ at 435 and 415 nm, respectively. The Cr(III)-quercetin-PVP and W(VI)-quercetin-cetylpyridinium bromide (CPB) systems are formed in the pH ranges 4–4.6 and 2.2–2.8 with molar absorptivities 1.02×10⁵ and 9.02×10⁴ L. mol⁻¹ cm⁻¹ at 441 and 419 nm, respectively. The linear dynamic ranges for the determination of Cr(III) and W(VI) with morin in the presence of EFA and PVP are 0.03–0.46 and 0.71–8.1 μg mL⁻¹, respectively. The corresponding ranges with quercetin are 0.04–0.54 and 0.14–2.1 μg mL⁻¹ of Cr(III) and W(VI), respectively. The r.s.d (n = 10) for the determination of 0.25 and 3.7 μg mL⁻¹ of Cr(III) and W(VI) with morin and their detection limits are 0.88 and 0.99% and 0.016 and 0.63 μg mL⁻¹, respectively. Using quercetin, the r.s.d (n = 10) for 0.22 and 1.2 μg mL⁻¹ of Cr(III) and W(VI) and their detection limits are 0.92 and 0.91% and 0.015 and 0.08 μg mL⁻¹, respectively. The critical evaluation of the proposed methods is performed by statistical analysis of the experimental data. The proposed methods are applied to determine Cr in steel, non-ferrous alloys, wastewater and mud filtrate and to the determination of W in steel. Received March 8, 1999. Revision January 21, 2000.     

Flow injection atomic absorption spectrometric determination of iodide using an on-line preconcentration technique

A continuous flow atomic absorption spectrometric system was used to develop an efficient on-line preconcentration-elution procedure for the determination of iodide traces. Chromium (VI) is introduced into the flow system and is reduced to chromium (III) in acid medium proportionally to the iodide present in the sample. The Cr(III) reduced by iodide is retained on a minicolumn packed with a poly(aminophosphonic acid) chelating resin, while unreduced Cr(VI) is not retained. Reduced Cr(III) is preconcentrated by passing the sample containing iodide through the system during 3 min, and is then eluted with 0.5 mol L(-1) hydrochloric acid and determined by flame atomic absorption spectrometry (FAAS). The detection limit (3sigma) obtained is 2.5 microg L(-1). Other ions typically present in waters do not interfere. The proposed method allows the determination of iodide in the range 6-220 microg L(-1) with a relative standard deviation of 2.7% at a rate of 17 samples h(-1). The method has been applied to the determination of iodide in tap and sea waters.     

Simultaneous determination of arsenic, selenium and antimony species using HPLC/ICP-MS

A new method for the simultaneous separation and determination of four arsenic species [As(III), As(V), monomethylarsonic acid and dimethylarsinic acid], three selenium species [Se(IV), Se(VI) and selenomethionine] as well as Sb(III) and Sb(V) is presented. The speciation was achieved by on-line coupling of anion exchange high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS). Chromatographic parameters such as the composition and pH of the mobile phase were optimised. Limits of detection are below 4.5 μg L^–1 (as element) for Sb(III) and the selenium species and below 0.5 μg L^–1 for the other species. Precisions of retention times were better than 2% RSD and of peak areas better than 8% RSD for all the species investigated. Received: 13 January 1999 / Accepted: 4 March 1999     

On-line preconcentration and speciation analysis of Cr(III) and Cr(VI) using baker's yeast cells immobilised on controlled pore glass

A study was undertaken to evaluate Saccharomyces cerevisiae as a substrate for the biosorption of Cr(III) and Cr(VI) aiming to the selective determination of these species in aqueous solutions. The yeast cells were covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. The effect of chemical and physical variables affecting the biosorption process was tested in order to select the optimal analytical conditions for the Cr retention by S. cerevisiae. Cr(III) was retained by the immobilised cells and Cr(VI) were retained by CPG. The speciation was possible by selective and sequential elution of Cr(III) with 0.05 mol L⁻¹ HCl and 2.0 mol L⁻¹ HNO₃ for Cr(VI). The influence of some concomitant ions up to 20 mg L⁻¹ was also tested. Quantitative determinations of Cr were carried out by means of inductively coupled plasma optical emission spectrometry (ICP OES). Preconcentration factors of 12 were achieved for Cr(III) and 5 for Cr(VI) when 1.7 mL of sample were processed reaching detection limits of 0.45 for Cr(III) and 1.5 μg L⁻¹ for Cr(VI). The speciation of inorganic Cr in different kinds of natural waters was performed following the proposed method. Spiked water samples were also analysed and the recoveries were in all cases between 81 and 103%.     

Evaluation of a commercially available microbore anion exchange column for chromium speciation with detection by ICP-mass spectrometry and hyphenation with microconcentric nebulization

The potential of a new commercially available microbore anion exchange column for chromium speciation (Cetac ANX-3202) was evaluated and its characteristics were studied. Nitric acid was used as mobile phase, making the technique ideal for coupling with inductively coupled plasma mass spectrometry (ICPMS). Because of the low operating flow rate of the column, a microconcentric nebulizer was used as an interface between the microbore column and the ICP-mass spectrometer. Co was added to the mobile phase and its signal intensity was continuously monitored and used as an internal standard to correct for signal drift and instrumental instability. Excellent results were obtained in terms of repeatability. Detection limits for Cr(III) and Cr(VI) are less than 1 μg · L^–1, using either ⁵²Cr or ⁵³Cr. The accuracy was determined by analyzing a certified reference material (BCR CRM 544). The concentrations found were in good agreement with those certified. The occurrence of C- and Cl-based molecular ions was studied and their influence on the determination of chromium was evaluated. Received: 8 August 1998 / Revised: 2 November 1998 / Accepted: 5 November 1998     

Flow injection spectrofluorimetric determination of iron(III) in water using salicylic acid

A simple and fast flow injection fluorescence quenching method for the determination of iron in water has been developed. Fluorimetric determination is based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The carrier solution used was 2 × 10⁻⁶ mol L⁻¹ salicylic acid in 0.1 mol L⁻¹ NH₄⁺/NH₃ buffer solution at pH 8.5. Linear calibration was obtained for 5–100 μg L⁻¹ iron(III) and the relative standard deviation was 1.25 % (n = 5) for a 20 μL injection volume iron(III). The limit of detection was 0.3 μg L⁻¹ and the sampling rate was 60 h⁻¹. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters).     

Hybrid mesoporous materials for on-line preconcentration of Cr(VI) followed by one-step scheme for elution and colorimetric determination at ultratrace levels

An hybrid mesoporous material synthesised in our laboratories for solid phase extraction (SPE) in flow through systems has been used for analytical purposes. The solid was obtained from mesoporous silica MCM-41 functionalized with 3-aminopropyltriethoxy silane by Sol-Gel methodology. In order to exploit the large sorption capacity of the material together with the possibility of modeling it for anions retention, a microcolumn (MC) filled with the solid was inserted in a flow system for preconcentration of Cr(VI) and its determination at ultratrace levels in natural waters. The analytical methodology involved a reverse flow injection system (rFI) holding a MC filled with the solid for the analyte extraction. Elution and colorimetric detection were carried out with 1-5 diphenylcarbazide (DPC) in sulfuric acid. DPC produced the reduction of Cr(VI) to Cr(III) together with the generation of a cationic red complex between Cr(III) and 1-5 diphenylcarbazone which was easily eluted and detected with a visible spectrophotometer. Moreover, the filling material got ready for the next sample loading remaining unspoiled for more than 300 cycles.The effect of several variables on the analytical signal as well as the influence of cationic and anionic interferences were discussed. Particular attention was given to sulfuric acid interference since it is the required media for the complex generation.Under optimal conditions, 99.8% of Cr(VI) recovery was obtained for a preconcentration time of 120 s (sample and DPC flow rates = 1 mL min⁻¹) and an elution volume of 250 μL. The limit of detection (3 s) was found to be 0.09 μg L⁻¹ Cr(VI) with a relative standard deviation (n = 10, 3 μg L⁻¹) of 1.8.Since no Cr(III) was retained by the solid material and Cr(VI) was completely adsorbed, electrothermal atomic absorption spectrometry (ET AAS) determinations of Cr(III) were also performed by simply measuring its concentration at the end of the microcolumn after Cr(VI) retention by the mesoporous solid.Applications to the determination of Cr(VI) and Cr(III) in natural waters and the validation of the methodology were also studied.     

A simple solid phase spectrofluorimetric method combined with flow analysis for the rapid determination of salicylamide and salicylic acid in pharmaceutical samples

A new, sensitive and very simple spectrofluorimetric biparameter sensor is described for the determination of salicylamide and/or salicylic acid in pharmaceutical preparations. The method integrates the transitory retention and fluorescence detection of both compounds on Sephadex QAE A-25 resin packed into a conventional flow-through cell. A monochannel manifold with two alternative carriers is used. At pH 2.0 (first carrier) salicylic acid is selectively retained on the solid support and after developing the analytical signal it is desorbed. At pH 11.0 (second carrier) both salicylic acid and salicylamide are simultaneously and transitorily retained on the solid, the analytical signal now corresponding to both analytes. The monochromators were tuned at 260 (excitation) and 415 (emission) nm, respectively. The calibration graph for salicylamide is linear over the range 0.01 to 0.32 μg mL^–1 and for salicylic acid from 0.04 to 1.0 μg mL^–1 in the presence of each other. The relative standard deviation and the sampling frequency for the determination of salicylamide (0.20 μg mL^–1) and salicylic acid (0.50 μg mL^–1) were 1.1% and 35 h^–1, and 0.9% and 45 h^–1, respectively. Good results on application to individual determination or mixture resolution in pharmaceutical samples testify to the usefulness of the proposed sensor. Received: 20 April 1999 / Revised: 7 June 1999 / Accepted: 12 June 1999     

Stabilization of antibodies by haptens

A new, sensitive and very simple spectrofluorimetric biparameter sensor is described for the determination of salicylamide and/or salicylic acid in pharmaceutical preparations. The method integrates the transitory retention and fluorescence detection of both compounds on Sephadex QAE A-25 resin packed into a conventional flow-through cell. A monochannel manifold with two alternative carriers is used. At pH 2.0 (first carrier) salicylic acid is selectively retained on the solid support and after developing the analytical signal it is desorbed. At pH 11.0 (second carrier) both salicylic acid and salicylamide are simultaneously and transitorily retained on the solid, the analytical signal now corresponding to both analytes. The monochromators were tuned at 260 (excitation) and 415 (emission) nm, respectively. The calibration graph for salicylamide is linear over the range 0.01 to 0.32 μg mL^–1 and for salicylic acid from 0.04 to 1.0 μg mL^–1 in the presence of each other. The relative standard deviation and the sampling frequency for the determination of salicylamide (0.20 μg mL^–1) and salicylic acid (0.50 μg mL^–1) were 1.1% and 35 h^–1, and 0.9% and 45 h^–1, respectively. Good results on application to individual determination or mixture resolution in pharmaceutical samples testify to the usefulness of the proposed sensor. Received: 20 April 1999 / Revised: 7 June 1999 / Accepted: 12 June 1999     

Speciation analysis of chromium by separation on a 5-palmitoyl oxine-functionalized XAD-2 resin and spectrophotometric determination with diphenylcarbazide

The method developed in this work for the separation and preconcentration of Cr(III) is based on its retention by an Amberlite XAD-2 copolymer resin functionalized with 5-palmitoyl-8-hydroxyquinoline (oxine), abbreviated XAD-POx, with the ligand covalently bound to the copolymer. Cr(III) sorption was quantitative within the pH range 4.5–7.0 and Cr(VI) was not retained. The Cr(III) held by the resin column was eluted with a hot solution of H₂O₂ in pH9.0 aqueous NH₃–NH₄Cl buffer, and Cr oxidized to CrO₄^2– was rejected by the chelating cation-exchanger column. Any Cr(VI) originally present with Cr(III) could be reduced with an acidic solution of H₂O₂, and retained by the column yielding total Cr results, Cr(VI) being determined from the difference. The resin showed a maximal preconcentration factor of 60 for Cr(III), the LOD and LOQ being 9.3 and 30.1 nmol L^–1, respectively. The developed preconcentration-speciation analysis was finished with a diphenylcarbazide (DPC) spectrophotometric procedure suitable for conventional laboratories. The resin showed excellent salt tolerance, enabling Cr analysis in seawater, and was stable over extended use. All the interferents of this procedure that normally occur in an electroplating effluent, a blended coal CRM, and a standard steel sample could be removed by the recommended procedure, by use of partial and total selectivity at the adsorption and desorption stages, respectively, enabling preconcentration and colorimetric determination of chromium in various complex matrices.     

Preconcentration and speciation of chromium using a melamine based polymeric sequestering succinic acid resin: its application for Cr(VI) and Cr(III) determination in wastewater

A new melamine based polymeric sequestering resin was prepared for preconcentration and separation of hexavalent chromium from water, and its sequestering action was investigated. The water-insoluble, cross-linked sequestering resin was formed by reaction with bromosuccinic acid and cross-linking of melamine. The active sequestering group on the resin is NH-(Succinic acid) or salt thereof. The resulting chelating resin was characterized by infrared spectra. The newly prepared resin quantitatively retained Cr(VI) at pH 2.0-4.0 when the flow rate was maintained between 1 and 5 ml min⁻¹. The retained Cr(VI) was instantaneously eluted with 25 ml of 0.1 M NaOH. The chromium species were determined by a flame atomic absorption spectrometer. The limits of detection for Cr(VI) and Cr(III) were found to be 5.3 and 4.2 μg l⁻¹, respectively. The precision and accuracy of the proposed procedure was checked by the use synthetic and reference steel samples. The established preconcentration method was successfully applied to the determination and selective separation of Cr(VI) in electroplating industry wastewater. Total concentrations determined by the spectrophotometric method (110.3±0.6 g l⁻¹ Cr(VI) and 1.2±0.3 g l⁻¹ Cr(III)) are compared with those found by FAAS and the obtained results (110.4±1.8 g l⁻¹ Cr(VI) and 1.4±0.5 g l⁻¹ Cr(III)) show good agreement.     

Speciation and determination of chromium ions by dispersive micro solid phase extraction using magnetic graphene oxide followed by flame atomic absorption spectrometry

A selective, simple and fast dispersive micro solid phase extraction method using magnetic graphene oxide (GO) as an efficient sorbent has been developed for the extraction, separation and speciation analysis of chromium ions. The method is based on different adsorption behaviour of Cr(VI) and Cr(III) species onto magnetic GO in aqueous solutions which allowed the selective separation and extraction of Cr(VI) in the pH range of 2.0–3.0. The retained Cr(VI) ions by the sorbent were eluted using 0.5 mL of 0.5 mol L^?1 nitric acid solution in methanol and determined by ?ame atomic absorption spectrometry. Total chromium content was determined after the oxidation of Cr(III) to Cr(VI) by potassium permanganate. All effective parameters on the performance of the extraction process were thoroughly investigated and optimised. Under the optimised conditions, the method exhibited a linear dynamic range of 0.5–50.0 µg L^?1 with a detection limit of 0.1 µg L^?1 and pre-concentration factor of 200. The relative standard deviations of 3.8% and 4.6% (n = 8) were obtained at 25.0 µg L^?1 level of Cr(VI) for intra- and inter-day analysis, respectively. The method was successfully applied to the speciation and determination of Cr(VI) and Cr(III) in environmental water samples.     

Indirect atomic absorption spectrometric determination of citric acid by continuous precipitation

A continuous precipitation and filtration flow system for the separation of citric acid by precipitation with lead and indirect flame atomic absorption spectrometry is proposed. The precipitate is formed by injecting the lead solution into a carrier containing the sample and is subsequently retained on a filter. By using this reversed precipitation flow-injection configuration, citric acid was determined in the range 2–40 μg mL^–1, with a relative standard deviation of 2.9% at a sampling frequency of 60 samples h^–1. This method has been applied to the determination of citric acid in fruit juices, carbonated soft drinks and sweets. Received: 19 March 1999 / Revised: 27 May 1999 / Accepted: 31 May 1999     

Development of a cloud point extraction and preconcentration method for chromium(III) and total chromium prior to flame atomic absorption spectrometry

A sensitive and selective method has been developed for the determination of chromium in water samples based on using cloud point extraction (CPE) preconcentration and determination by flame atomic absorption spectrometry (FAAS). The method is based on the complexation of Cr(III) ions with Brilliant Cresyl Blue (BCB) in the presence of non-ionic surfactant Triton X-114. Under the optimum conditions, the preconcentration of 50 mL of water sample in the presence of 0.5 g/L Triton X-114 and 1.2 × 10⁻⁵ M BCB permitted the detection of 0.42 μg/L chromium(III). The calibration graph was linear in the range of 1.5–70 μg/L, and the recovery of more than 99% was achieved. The proposed method was used in FAAS determination of Cr(III) in water samples and certified water samples. In addition, the developed CPE-FAAS method was also used for speciation of the inorganic chromium species after reduction of Cr(VI) to Cr(III) using a thiosulphate solution of 120 mg/L in the presence of Hg(II) ion as a stabilizer.     

Determination of trace chromium(VI) in drinking water using X-ray fluorescence spectrometry after solid-phase extraction

A new, simple, and selective method for preconcentration and determination of Cr(VI) in aqueous samples. After adsorption in “batch mode” on Aliquat 336-AC, determinations were made directly on the solid by X-ray fluorescence spectrometry, which had the advantage of not requiring the step of elution of the chromium retained. The enrichment factor was calculated considering that the tablets obtained from 10 mL solution of Cr(VI) (1000 μg L^-1) had a final thickness of 0.64 mm and a diameter of 16.7 mm; the volume deposited on the pellet was 0.14 cm³. The preconcentration factor obtained was 71-fold, which was highly satisfactory for chromium trace analysis by XRF. Finally, the method was successfully applied to the determination of Cr(VI) in drinking water samples.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-Butylcalix[8]arene loaded silica gel for preconcentration of uranium(VI) via solid phase extraction

This paper reports silica gel loaded with p-tert-butylcalix[8]arene as a new solid phase extractor for determination of trace level of uranium. Effective extraction conditions were optimized in column methods prior to determination by spectrophotometry using arsenazo(III). The results showed that U(VI) ions can be sorbed at pH 6 in a mini-column and quantitative recovery of U(VI) (>95–98%) was achieved by stripping 0.4 mol L⁻¹ HCl. The sorption capacity of the functionalized sorbent is 0.072 mmol uranium(VI) g⁻¹ modified silica gel. The relative standard deviation and detection limit were 1.2% (n = 10) for 1 μg uranium(VI) mL⁻¹ solution and 0.038 μg L⁻¹, respectively. The method was employed to the preconcentration of U(VI) ions from spiked ground water samples.     

Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration

A minicolumn packed with poly(aminophosphonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at μg L^–1 level. The preconcentrated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The performance characteristics of the determination of lead were: preconcentration factor 26.8 for 1 min preconcentration time, detection limit (3σ) in the sample digest was 0.25 μg g^–1 (dry weight) for a sample volume of 3.5 mL and 0.2 g sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 μg L^–1 and 2.0% for 50 μg L^–1. The sampling frequency was 45 h^–1. The method was highly tolerant of interferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples. Received: 1 November 2000 / Revised: 8 January 2001/ Accepted: 11 January 2001