Determination of copper by electrothermal AAS after electrodeposition on a graphite disk electrode

The electrodeposition of copper on a graphite electrode at a constant potential with subsequent atomization in the graphite atomizer HGA-400 has been studied. A special graphite disk electrode is suitable for electrochemical enrichment at E = -0.7 V vs. SCE and the determination of copper by electrothermal-atomic absorption spectrometry (ET-AAS) if atomized at 2300 degrees C. In this way copper was determined in potable water and free Cu(2+) could be distinguished from that bound in chelate speciations after using a suitable deposition potential of the working electrode. This approach seems to be an alternative to the commonly used anodic stripping voltammetry (ASV) for the preconcentration and determination of free metal ions.     

Fluorimetric Cr(VI) and Cr(III) Speciation With Crystal Violet

Abstract

A simple fluorimetric determination of Cr(VI) in the presence of Cr(III) is described. This determination is based on the fluorescence, produced from the ion-association complex between the Crystal violet cation and the anionic complex, formed between Cr(VI) and excess of I^?. This fluorescence is not observed when Cr(III) is used instead of Cr(VI). The fluorescence intensity is linear over the concentration range of 0–60 μg/1. The method was applied in potable and sea waters.     

Speciation of Cr(III) and Cr(VI) by Means of Melamine-Urea-Formaldehyde Resin and FAAS

 A method is described for the quantitative preconcentration and separation of trace chromium in water by adsorption on melamine-urea-formaldehyde resin. Cr(VI) is enriched from aqueous solutions on the resin. After elution the Cr(VI) is determined by FAAS. The capacity of the resin is maximal at ∼ pH 2. Total chromium can be determined by the method after oxidation of Cr(III) to Cr(VI) by hydrogen peroxide. The relative standard deviations (10 replicate analyses) for 10 mg/L levels of Cr(VI), Cr(III) and total chromium were 1.5, 3.5 and 2.8% respectively. The procedure has been applied to the determination and speciation of chromium in lake water, tap water and chromium-plating baths.     

Speciation Analysis of Cr(III) and Cr(VI) after Solid Phase Extraction Using Modified Magnetite Nanoparticles

A new solid phase extraction (SPE) method has been developed for the speciation of Cr(III) and Cr(VI). This method is based on the adsorption of Cr(VI) on modified alumina‐coated magnetite nanoparticles (ACMNPs). Total chromium in different samples was determined as Cr(VI) after oxidation of Cr(III) to Cr(VI) using H₂O₂. The chromium concentration has been determined by flame atomic absorption spectrometric (FAAS) technique and amount of Cr(III) was calculated by substracting the concentration of Cr(VI) from total chromium concentration. The effect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, H₂O₂ concentration and cetyltrimethylammonium bromide (CTAB) concentration as modifier on the quantitative recovery of Cr(VI) were investigated. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation (RSD) of Cr(VI) were 140 (for 350 mL of sample solution), 0.083 ng mL^?1, 0.1‐10.0 ng mL^?1 and 4.6% (for 5.0 ng mL^?1, n = 7), respectively. This method avoided the time‐consuming column‐passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of chromium in different water and wastewater samples and suitable recoveries were obtained.     

Speciation of Cr(III) and Cr(VI) by reversed phase high-performance liquid chromatography using UV-detection

Summary A method for the simultaneous determination of Cr(III) and Cr(VI) in water samples is described. The different reaction products of Cr(III) and Cr(VI) species with ammonium pyrrolidinedithiocarbamate (APDC) are extracted with ethyl acetate and determined by reversed phase HPLC using UV-detection. The procedure is optimized and its detection limit accordingly improved as compared to literature data. The detection limits achieved are 2.4 g/l for Cr(III) and 2.1 g/l for Cr(VI) and the calibration curves are linear between 5 g/l and 5000 g/l. For the speciation of Cr, APDC was demonstrated to be more suitable as chelating agent than sodium diethyldithiocarbamate (NaDDC). The procedure was applied to the determination of both Cr species in galvanic waste waters and its accuracy was approved by comparing the results (at the 100 g/l level) with those of a photometric determination of Cr(VI) species.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Speciation of Cr(VI)/Cr(III) in environmental waters by fluorimetric method using central composite, full and fractional factorial design

In this approach a fluorometric technique has been developed to study chromium speciation, based on optimised conditions using chemometric methods of experimental design and central composite design. Full and fractional factorial design was used for evaluation of the effective factors in determination of Cr(VI) by fluorometric using Rhodamine-6G in the presence of H₂SO₄. Theory and methodology of a central composite design as a chemometric method for the optimisation of analytical procedures were developed in this approach. It was found that the analytical performance for measurement at the point of optimum in this technique is superior and more accurate than that of one variable at a time. Cr(VI) and Cr(III) were measured in a wastewater sample using the proposed technique. The results confirm the selective determination and speciation of Cr(VI)/Cr(III).     

Protocol for Extraction and Determination of Cr(VI) in Solid Materials with a High Cr(III)/Cr(VI) Ratio Using EDDS as a Leaching Agent for Cr(VI) and a Masking Agent for Cr(III)

A sensitive and selective protocol for the extraction of all forms of Cr(VI) from solid materials followed by determination by catalytic adsorptive stripping voltammetry has been elaborated. Cr(VI) was leached to a solution with 0.2 mol L^?1 (NH₄)₂SO₄/NH₄OH+0.1 mol L^?1 EDDS (pH 9.5) and simultaneously Cr(III) was transferred to a nonactive electrochemical complex with EDDS. The method allows for Cr(VI) determination in solid samples containing even a 1000–2000 fold excess of extractable Cr(III) without its noticeable influence. The effects of several experimental variables such as the composition and pH of the extractant, the time and temperature of the solid sample mixing with the extractant were studied. At the optimized conditions more than 95% of total Cr(VI) recoveries from solid samples were achieved. The validation of the proposed procedure was carried out by Cr(VI) determination in certified reference material CRM 019 Ash, spiked and unspiked with Cr(III), and by comparing the obtained results with those obtained using other common extraction procedures.     

A nanoparticle sorbent composed of MIL-101(Fe) and dithiocarbamate-modified magnetite nanoparticles for speciation of Cr(III) and Cr(VI) prior to their determination by electrothermal AAS

Microchimica Acta - The article describes a magnetic metal-organic framework (MOF) of the type MIL-101(Fe)/2-(propylamino-ethyl) dithiocarbamate on the surface of magnetite nanoparticles. The MOF...     

Speciation of Cr(III) and Cr(VI) in Environmental Samples after Solid Phase Extraction on Amberlite XAD–2000

A method for speciation of Cr(III) and Cr(VI) in real samples has been developed. Cr(VI) has been separated from Cr(III) and preconcentrated as its pyrrolidinedithiocarbamate (APDC) complex by using a column containing Amberlite XAD–2000 resin and determined by FAAS. Total chromium has also been determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with KMnO₄. Cr(III) has been calculated by subtracting Cr(VI) from the total. The effect of pH, flow‐rate, adsorption and batch capacity and effect of various metal cations and salt anions on the sorption onto the resin were investigated. The adsorption is quantitative in the pH range of 1.5–2.5, and Cr(VI) ion was desorbed by using H₂SO₄ in acetone. The recovery of Cr(VI) was 97 ± 4 at a 95% confidence level. The highest preconcentration factor was 80 for a 200 mL sample volume. The adsorption and batch capacity of sorbent were 7.4 and 8.0 mg g^?1 Cr(VI), respectively, and loading half time was 5.0 min. The detection limit of Cr(VI) is 0.6 μg/L. The procedure has been applied to the determination and speciation of chromium in stream water, tap water, mineral spring water and spring water. Also, the proposed method was applied to total chromium preconcentration in microwave digested moss and rock samples with satisfactory results. The developed method was validated with CRM‐TMDW‐500 (Certified Reference Material Trace Metals in Drinking Water) and BCR‐CRM 144R s (Certified Reference Material Sewage Sludge, Domestic Origin) and the results obtained were in good agreement with the certified values. The relative standard deviations were below 6%.     

Speciation of Cr(III) and Cr(VI) in waters using immobilized moss and determination by ICP-MS and FAAS

The possibility of using moss (Funaria hygrometrica), immobilized in a polysilicate matrix as substrate for speciation of Cr(III) and Cr(VI) in various water samples has been investigated. Experiments were performed to optimize conditions such as pH, amount of sorbent and flow rate, to achieve the quantitative separation of Cr(III) and Cr(VI). During all the steps of the separation process, Cr(III) was selectively sorbed on the column of immobilized moss in the pH range of 4-8 while, Cr(VI) was found to remain in solution. The retained Cr(III) was subsequently eluted with 10 ml of 2 mol l⁻¹ HNO₃. A pre-concentration factor of about 20 was achieved for Cr(III) when, 200 ml of water was passed. The immobilized moss was packed in a home made mini-column and incorporated in flow injection system for obtaining calibration plots for both Cr(III) and Cr(VI) at low ppb levels that were compared with the plots obtained without column. After separation, the chromium (Cr) species were determined by inductively coupled plasma mass spectrometry (ICP-MS) and flame atomic absorption spectrometry (FAAS). The sorption capacity of the immobilized moss was found to be ∼11.5 mg g⁻¹ for Cr(III). The effect of various interfering ions has also been studied. The proposed method was applied successfully for the determination of Cr(III) and Cr(VI) in spiked and real wastewater samples and recoveries were found to be >95%.     

Speciation of Cr(III) and Cr(VI) in water after preconcentration of its 1,5-diphenylcarbazone complex on amberlite XAD-16 resin and determination by FAAS

A simple and sensitive method for the speciation, separation and preconcentration of Cr(VI) and Cr(III) in tap water was developed. Cr(VI) has been separated from Cr(III) and preconcentrated as its 1,5-diphenylcarbazone complex by using a column containing Amberlite XAD-16 resin and determined by FAAS. Total chromium has also been determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with KMnO₄. Then, Cr(III) has been calculated by subtracting Cr(VI) from the total. The effect of acidity, amount of adsorbent, eluent type and flow rate of the sample solution on to the preconcentration procedure has been investigated. The retained Cr(VI) complex was eluated with 10 ml of 0.05 mol l⁻¹ H₂SO₄ solution in methanol. The recovery of Cr(VI) was 99.7±0.7 at 95% confidence level. The highest preconcentration factor was 25 for a 250 ml sample volume. The detection limit of Cr(VI) was found as 45 μg l⁻¹. The adsorption capacity of the resin was found as 0.4 mg g⁻¹ for Cr (VI). The effect of interfering ions has also been studied. The proposed method was applied to tap water samples and chromium species have been determined with the relative error <3%.     

Measurement of Cr(III)/Cr(VI) species by wavelength modulation diode laser flame atomic absorption spectrometry

High-performance flow atomic spectrometry of Cr(III) and Cr(VI) species by high-performance liquid chromatography (HPLC) separation, hydraulic high-pressure nebulization (HHPN) for sample introduction and wavelength modulation-laser atomic absorption spectrometry (WM-LAAS) with diode lasers in an analytical flame is reported. 3σ detection limits of 0.5 and 1 ng ml⁻¹ have been obtained for Cr(VI) in deionized and drinking water, respectively. Due to relatively high blank levels, the corresponding detection limits of Cr(III) are higher than for Cr(VI), i.e. 1.6 ng ml⁻¹ in deionized water and 5 ng ml⁻¹ in drinking water.     

Speciation of Cr(III) and Cr(VI) in environmental samples by using coprecipitation with praseodymium(III) hydroxide and determination by flame atomic absorption spectrometry

A speciation procedure has been established for the flame atomic absorption spectrometric determination of Cr(III) and Cr(VI) based on coprecipitation of Cr(III) by using praseodymium(III) hydroxide (Pr(OH)₃) precipitate. In the presented system, Cr(III) was quantitatively (>95%) recovered at the pH range of 10.0?C12.0 on Pr(III) hydroxide, while the recoveries of Cr(VI) were below 10%. The method was applied to the determination of the total chromium after reduction of Cr(VI) to Cr(III) by using hydroxylamine hydrochloride. The concentration of Cr(VI) is calculated by difference of total chromium and Cr(III) levels. The analytical parameters including pH of the aqueous medium, amount of Pr(III), centrifugation speed, sample volume were optimized. The influences of matrix ions were also investigated. The method was validated by the analysis of TMDA 70 fortified lake water certified reference material. The method was applied to the speciation of chromium in water samples.     

Cr(III)/Cr(VI) determination in waste water by ICP/AES with on-line HPLC (HHPN) sample introduction

Using hydraulic high-pressure nebulization (HHPN) for sample introduction, an on-line high-pressure flow system (HPLC system) becomes a functional component of the ICP spectrometer. By placing additionally an HPLC column between the sample valve and the high-pressure injection/nebulization nozzle, an improved species analysis is attained. An example is given by on-line separation and determination of Cr(III)/Cr(VI) in real waste water samples with ICP/AES. The detection limit of each Cr oxidation state is 4 μg L^–1 with an analysis cycle time of 5 min. In comparison to conventional coupling of HPLC and ICP spectrometry a considerably higher sensitivity is achieved. Using spiked samples the recovery of HHPN-ICP/AES was on an average better than 98% in contrast to only 79% for Cr(VI) determination with a UV photometric reference method. Due to chromatographic separation of Cr(VI) from matrix components and Cr (III), the technique no longer shows the typical spectral interferences caused by Ca (267.716 nm Cr line) and Fe (283.563 nm Cr line). Received: 2 August 1997 / Revised: 11 October 1997 / Accepted: 21 October 1997     

Cr(III)/Cr(VI) determination in waste water by ICP/AES with on-line HPLC (HHPN) sample introduction

Using hydraulic high-pressure nebulization (HHPN) for sample introduction, an on-line high-pressure flow system (HPLC system) becomes a functional component of the ICP spectrometer. By placing additionally an HPLC column between the sample valve and the high-pressure injection/nebulization nozzle, an improved species analysis is attained. An example is given by on-line separation and determination of Cr(III)/Cr(VI) in real waste water samples with ICP/AES. The detection limit of each Cr oxidation state is 4 μg L^–1 with an analysis cycle time of 5 min. In comparison to conventional coupling of HPLC and ICP spectrometry a considerably higher sensitivity is achieved. Using spiked samples the recovery of HHPN-ICP/AES was on an average better than 98% in contrast to only 79% for Cr(VI) determination with a UV photometric reference method. Due to chromatographic separation of Cr(VI) from matrix components and Cr (III), the technique no longer shows the typical spectral interferences caused by Ca (267.716 nm Cr line) and Fe (283.563 nm Cr line).     

Speciation of Cr(III) and Cr(VI) in potable waters by using activated neutral alumina as collector and ET-AAS for determination

The speciation of Cr(III) and Cr(VI) has been performed by using activated neutral alumina as adsorbent. Both species were quantitatively adsorbed on a small column filled with neutral alumina. The adsorbed Cr(III) was eluted with 4 mol L(-1) HNO(3) and Cr(VI) with 1.0 mol L(-1) ammonia solution. Recoveries of Cr(III) and Cr(VI) were 99% and 100%, respectively. Using ET-AAS for Cr determination the limit of detection in the sample was 0.01 microg L(-1). The combined procedure is fast and sensitive. It can be applied for routine analysis of water samples at sub-microg L(-1) levels with a relative standard deviation (RSD) of 2-10% (three determinations).     

Methodische Ans?tze zur Cr(III)/Cr(VI)-Speciesanalyse mit Hilfe der elektrothermalen Atomabsorptionsspektrometrie

Zusammenfassung Die Übertragung von chemischen Reaktionen im makroskopischen Maßstab auf die in der elektrothermalen AAS notwendigen geringen Substanzmengen im Sinne einer Graphitrohrofenchemie (GOC) bildet die Grundlage für Ansätze zu einer Metallspeciesanalyse. Beschrieben werden die Differenzierung von Cr(III)- und Cr(VI)-Species nach Umsetzung mit Trifluoracetylaceton in der Atomisierungseinheit, sowie die dabei auftretenden Probleme und Fehler. Eine Langzeitkonstanz für Cr-AAS-Signale wird durch Standardisierung der inneren Graphitrohroberfläche erhalten. Das Verfahren eignet sich zum screening bei human- oder ökotoxikologischen Fragestellungen.

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Methodical developments for the speciation of Cr(III)/Cr(VI) by electrothermal atomic absorption spectrometry

Summary Graphite furnace chemistry (GFC) is the basis for metal speciation by electrothermal atomic absorption spectrometry. The differentiation of Cr(III) and Cr(VI) becomes possible after reacting the Cr(III) with trifluoracetylacetone inside the graphite furnace. Problems and errors of the procedure are described as well as its optimization. A long-term stability of the AAS-signals of chromium can be obtained by a chemical standardization of the inner surface of the tubes. The procedure can be used as a screening test in human- or ecotoxicology.

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Herrn Prof. Dr. H. Monien zum 60. Geburtstag gewidmet