Preconcentration of palladium(II) from water with thionalide loaded on silica gel

2-Mercapto-N-2-naphthylacetamide (thionalide) on silica gel is used for rapid preconcentration of μg l^?1 levels of palladium(II) from aqueous solution, followed by atomic absorption spectrometric measurement. In batch experiments, palladium was quantitatively retained on the gel from solutions 5 M in acid to pH 8; equilibrium was achieved within 10 s. The chelating capacity of the gel was 7.5 μmol Pd g^?1 at pH < 4. The effect of flow rate on retention was studied. Palladium retained on the column was completely eluted with 20 ml of 0.2 M thiourea in 0.1 M hydrochloric acid. The palladium concentration in sea water is shown to be < 0.3 μg l^?1.     

Determination of antimony(III,V) in natural waters by separation and preconcentration on a thionalide loaded resin followed by neutron activation analysis

A chelating sorbent obtained by immobilization of thionalide on the macroporous resin Bio Beads SM-7 was used for speciation of antimony(III) and (V) in natural waters. Antimony(III) was separated from Sb(V) by sorption on a column with the sorbent at pH 5. Antimony(V) in the effluent was reduced to Sb(III) and preconcentrated by sorption on the sorbent from 0.5M HCl solution. Both the separated species were determined directly on the sorbent by neutron activation analysis.     

Speciation of arsenic(III) and arsenic(V) by inductively coupled plasma-atomic emission spectrometry coupled with preconcentration system

A novel and simple flow-based method was developed for the simultaneous determination of As(III) and As(V) in freshwater samples. Two miniature columns with a solid phase anion exchange resin, placed on two 6-way valves were utilized for the solid-phase collection/concentration of arsenic(III) and arsenic(V), respectively. As(III) could be retained on the column after its oxidation to As(V) species with an oxidizing agent. The collected analytes were then sequentially eluted by 2 M nitric acid and introduced into ICP-AES. Potassium permanganate was examined as potential oxidizing agent for conversion of As(III) to As(V). The standard deviation of the analytical signals (peak height) for the replicate analysis (n = 5) of 0.5 μg l⁻¹ solution were 3 and 5% for As(III) and As(V), respectively. The limit of detection (3σ) for both As(III) and As(V) were 0.1 μg l⁻¹. The proposed system produced satisfactory results on the application to the direct analysis of inorganic arsenic species in freshwater samples.     

Fluoride-fluorosulfates of arsenic (V) and arsenic (III)

The synthesis of AsF₃(SO₃F)₂ by the reaction AsF₃ + S₂O₆F₂→AsF₃(SO₃F)₂ is described. Various alternate routes leading to similar arsenic (V) fluoride-fluorosulfates are discussed. All materials are clear, viscous, strongly associated liquids of the general formula AsF_n(SO₃F)_5?n, with n ranging from about 2 to 4. The presence of fluorosulfate bridges is ascertained by IR and Raman spectra.The spectroscopic investigation is also extended to arsenic (III) fluoride- fluorosulfates.     

Differential pulse voltammetric determination of arsenic(III,V) and antimony (III,V) in glasses

Summary Analytical methods based on differential pulse voltammetry (DPV) have been described for the determination of total As, As(III), As(V), total Sb and Sb(III) as trace to minor constituents in complex glasses. For total As, the sample is decomposed with HF-H₂SO₄-KMnO₄. The As(V) is chemically reduced to As (III) by hypophosphite and a DPV scan is carried out at the dropping mercury electrode from –0.2 to –0.7 Vvs. SCE (E _p –0.41V). As(V) is determined by decomposing the sample in HF-H₂SO₄ and volatilizing the As(III) as AsF₃. The chemical reduction of As(V) and the DPV scan are then applied. If the glass can be decomposed with cold HF, the As(III) present in the glass can be determined by applying the DPV scan after cold sample-dissolution. For Sb(III), the sample is decomposed with HF-H₂SO₄, diluted, and adjusted to 1M in HCl. A DPV scan is conducted from –0.03 to –0.5 V (E _p –0.15 V). Sb(V) is not reduced in the 1M HCl supporting electrolyte. Total Sb is determined by using an aliquot of the sample solution adjusted to 6M in HCl. The DPV sweep is carried out from –0.5 to –0.1 V [E _p for Sb(V) and Sb(III) is –0.30 V]. The methods have been applied to a wide range of glass compositions and the results compared with values obtained by spectrophotometry and coulometric titration.

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Bestimmung von Arsen(III, V) und Antimon(III, V) in Gläsern mit Hilfe der Differential-Puls-Voltammetrie

Zusammenfassung Analytische Methoden auf der Grundlage der Differential-Puls-Voltammetrie (DPV) für die Bestimmung des gesamten Arsens, As(III), As(V), des gesamten Antimons und Sb(III) als Spuren in komplexen Gläsern wurden beschrieben. Zwecks Bestimmung des Gesamt-As wird die Probe mit Flußsäure +Schwefelsäure + Permanganat aufgeschlossen. As(V) wird mit Hypophosphit reduziert und die DPV wird an einer Quecksilber-Tropfelektrode zwischen –0,2 und –0,7V gegen eine ges. Kalomelelektrode (E _p =–0,41V) durchgeführt. Zur Bestimmung von As(V) wird die Probe mit HF-H₂SO₄ unter Verflüchtigung des As(III) als AsF₃ aufgeschlossen. Dann erfolgt die Reduktion des As(V) und die DPV. Wenn sich das Glas mit kalter HF lösen läßt, wird anwesendes As(III) mittels DPV in dieser Lösung bestimmt. Zur Bestimmung des Sb(III) wird die Probe mit HF-H₂SO₄ zersetzt, verdünnt und bis zur 1-Molarität mit HCl versetzt. Dann wird mit DPV zwischen –0,03 und –0,5V gemessen (E _p =–0,15V). Sb(V) wird in 1M salzsaurer Lösung nicht reduziert. Das Gesamt-Sb wird in einem Aliquot der Probelösung bestimmt, das dazu mit HCl bis zur 6fachen Molarität versetzt wird. Der DPV-Bereich wird von –0,5 bis –0,1 V ausgenützt (E _p f:ur Sb(V) und Sb(III) ist –0,30 V). Das Verfahren wurde für Gläser verschiedenster Zusammensetzung angewendet. Die Ergebnisse wurden mit den Resultaten der Spektrophotometrie und der coulometrischen Titration verglichen.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Selective preconcentration of Au(III), Pt(IV) and Pd(II) on silica gel modified with γ-aminopropyltriethoxysilane

Silica gel functionalized by reaction with γ-aminopropyltriethoxysilane was prepared and its adsorption characteirstics for metal ions were studied. This material selectively removes the Au(III), Pt(IV) and Pd(II) chloro complex ions from sample solutions containing Fe(III) and Cu(II) ions by ion exchange.     

Preconcentration of antimony(III) from water with thionalide loaded on glass beads with the aid of collodion

2-Mercapto-N-2-naphthylacetamide (thionalide) loaded on glass beads with the aid of collodion is used for preconcentration of microgram levels of antimony(III) from aqueous solution. Antimony is quantitatively retained on the loaded beads from 0.4–0.8 mol l^?1 hydrochloric acid solutions; equilibration is achieved within 1 min. The retention capacity of the beads is 0.2 μml Sb g^?1 at 0.6 mol l^?1 hydrochloric acid. The maximum flow rate for quantitative retention is 1.27 ml min^?1 cm^?2. Antimony retained on the column is completely eluted with 10 ml of 6.0 mol l^?1 hydrochloric acid at flow rates<1.9 ml min^?1 cm^?2.     

Differential determination of arsenic(III) and total arsenic using flow injection on-line separation and preconcentration for graphite furnace atomic absorption spectrometry

Arsenic(III) can be quantitatively extracted using sodium diethyldithiocarbamate (NaDDTC) as the complexing agent and C18 reversed phase packing as the column material for solid phase extraction. Arsenic(V) must be reduced to its trivalent oxidation state prior to extraction. A mixture of sodium sulphite, hydrochloric acid, sodium thiosulphate and potassium iodide was found to be optimum for on-line reduction. When the sorbent extraction is carried out without and with the addition of the reduction mixture, arsenic(III) and total arsenic can be determined sequentially by graphite furnace atomic absorption spectrometry with detection limits (3 σ) of 0.32 ng for As(III) and 0.43 ng for total arsenic. A 7.6-fold enhancement in peak area compared to direct injection of 40 μl samples was obtained after 60 s preconcentration. Results obtained for sea water standard reference materials, using aqueous standards for calibration, agree well with certified values. A precision of 5.5% RSD was obtained for total arsenic in a sea water sample (1.65 As). Results obtained for synthetic mixtures of trivalent and pentavalent arsenic agreed well with expected values.     

Determination of arsenic(III) and arsenic(V) by electrothermal atomic absorption spectrometry after complexation and sorption on a C-18 bonded silica column

A flow injection procedure for the separation and pre-concentration of inorganic arsenic based on the complexation with ammonium diethyl dithiophosphate (DDTP) and sorption on a C-18 bonded silica gel minicolumn is proposed. During the sample injection by a time-based fashion, the As³⁺-DDTP complex is stripped from the solution and retained in the column. Arsenic(V) and other ions that do not form complexes are discarded. After reduction to the trivalent state by using potassium iodide plus ascorbic acid, total arsenic is determined by electrothermal atomic absorption spectrometry (ETAAS). Arsenic(V) concentration can be calculated by difference. After processing 6 ml sample volume, the As³⁺-DDTP complexes were eluted directly into the autosampler cup (120 μl). Ethanol was used for column rinsing. Influence of pH, reagent concentration, pre-concentration and elution time and column size were investigated. When 30 μl of eluate plus 10 μl of 0.1% (w/v) Pd(NO₃)₂ were dispensed into the graphite tube, analytical curve in the 0.3–3 μg As l⁻¹ range was obtained (r=0.9991). The accuracy was checked for arsenic determination in a certified water, spiked tap water and synthetic mixtures of arsenite and arsenate. Good recoveries (97–108%) of spiked samples were found. Results are precise (RSD 7.5 and 6% for 0.5 and 2.5 μg l⁻¹, n=10) and in agreement with the certified value of reference material at 95% confidence level.     

Separation of arsenic(III) and arsenic(V) in ground waters by ion-exchange

The predominant species of arsenic in ground water are probably arsenite and arsenate. These can be separated with a strong anion-exchange resin (Dowex 1 x 8; 100-200 mesh, acetate form) in a 10 cm x 7 mm column. Samples are filtered and acidified with concentrated hydrochloric acid (1 ml per 100 ml of sample) at the sample site. Five ml of the acidified sample are used for the separation. At this acidity, As(III) passes through the acetate-form resin, and As(V) is retained. As(V) is eluted by passage of 0.12M hydrochloric acid through the column (resulting in conversion of the resin back into the chloride form). Samples are collected in 5-ml portions up to a total of 20 ml. The arsenic concentration in each portion is determined by graphite-furnace atomic-absorption spectrophotometry. The first two fractions give the As(III) concentration and the last two the As(V) concentration. The detection limit for the concentration of each species is 1 mug l .     

Reversed-phase extraction chromatography of iron(III) with tri-n-butyl phosphate on silica gel

Iron(III) is separated by reversed-phase extraction chromatography with TBP as the stationary phase on a column of silica gel, with 2-6M hydrochloric acid as the mobile phase. From knowledge of the distribution coefficients, several separations have been devised, such as separation of Fe(III) from alkali and alkaline earth metals, chromium, manganese, cobalt, nickel, copper, vanadium zirconium, thorium, uranium, yttrium and titanium.     

Differential determination of arsenic(III) and arsenic(V), and antimony(III) and antimony(V) by hydride generation-atomic absorption spectrophotometry,and its application to the determination of these species in sea water

A method is described for the differential determination of As(III) and As(V). and Sb(III) and Sb(V) by hydride generation-atomic absorption spectrophotometry with hydrogen-nitrogen flame using sodium borohydride solution as a reductant. For the determination of As(III) and Sb(III), most of the elements, other than Ag⁺, Cu²⁺, Sn²⁺, Se⁴⁺ and Te⁴⁺, do not interfere in an at least 30,000 fold excess with respect to As(III) or Sb(III). This method was applied to the determination of these species in sea water and it was found that a sample size of only 100 ml is enough to determine them with a precision of 1.5–2.5%. Analytical results for surface sea water of Hiroshima Bay were 0.72 μgl^?1, 0.27 μgl^?1 and 0.22 μgl^?1 for As(total), As(III) and Sb(total), respectively, but Sb(III) was not detected in the present sample. The effect of acidification on storage was also examined.     

Sorption and preconcentration of copper and cadmium on silica gel modified with 3-aminopropyltriethoxysilane

3-Aminopropyltriethoxysilane, (C₂H₅O)₃ Si(CH₂)₃NH₂, loaded on silica gel was used as a pre-concentration sorbent for copper and cadmium prior to their determination by flame atomic absorption spectrometry (FAAS). Both batch and column methods were used for the separation of the above metals. The analytes are quantitatively retained on the proposed adsorbent at pH 6.5. The complexation capacity of the collector is 0.032 mmol Cu/g silica. In the batch method, the effects of shaking time and the ratio of metal/silica on the retention by the asorbent were investigated. Columns filled with the collector provided quantitative recovery of the above metals from standardized samples as well as from sodium chloride solutions.     

Speciation of arsenic(V) and arsenic(III) by cathodic stripping voltammetry in fresh water samples

A voltammetric stripping procedure is described for the determination of arsenic(V) in a mannitol-sulphuric acid medium. The arsenic is coprecipitated with copper and selenium and reduced to arsine at the hanging mercury drop electrode. Using an accumulation time of 240 s, the detection limit is 0.52 μg L^–1, the determination limit is 0.9 μg L^–1. The method has been applied to the determination of arsenic in water samples. By varying the composition of the supporting electrolyte it is possible to differentiate between arsenic(III) and arsenic(V). As both oxidation states have different toxicological characteristics, the ability to discriminate between both is an distinct advantage of the proposed method. Received: 25 October 1996 / Revised: 7 February 1997 / Accepted: 12 February 1997     

Adsorption of arsenic(III) and arsenic(V) from groundwater using natural siderite as the adsorbent

Batch and column tests were performed utilizing natural siderite to remove As(V) and As(III) from water. One hundred milligrams of siderite was reacted at room temperature for up to 8 days with 50 mL of 1000 microg/L As(V) or As(III) in 0.01 M NaCl. Arsenic concentration decreased exponentially with time, and pseudoequilibrium was attained in 3 days. The estimated adsorption capacities were 520 and 1040 microg/g for As(V) and As(III), respectively. Column studies show that effluent As was below 1.0 microg/L after a throughput of 26,000 pore volumes of 500 microg/L As water, corresponding to about 2000 microg/g of As load in the filter. Results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that high As retention capacity of the filter arose from coprecipitation of Fe oxides with As and subsequent adsorption of As on the fresh Fe oxides/hydroxides. Arsenic adsorption in the filter from As-spiked tap water was relatively lower than that from artificial As solution because high HCO(-)(3) concentration restrained siderite dissolution and thus suppressed production of the fresh Fe oxides on the siderite grains. The TCLP (toxicity characteristic leaching procedure) results suggest that these spent adsorbents were inert and could be landfilled.     

Selective solid phase extraction and preconcentration of iron(III) based on silica gel-chemically immobilized purpurogallin

The immobilization of purpurogallin on the surface of amino group containing silica gel phase for the formation of a newly synthesized silica gel-bound purpurogallin (SGBP) is described. The surface modification was studied and evaluated by determination of the surface coverage value by both the elemental analysis and metal probe testing method, which was found to be 0.485 and 0.460 mmol g⁻¹, respectively. The metal sorption properties of SGBP were examined by a series of di- and tri-valent metal ions. The metal capacity values (mmol g⁻¹) for this series of metal ions were also determined under different buffer solutions (pH 1.0–6.0) as well as shaking times by the batch equilibrium technique. The results of this study confirmed the strong affinity and selectivity as well as the fast equilibration and interaction processes of SGBP and Fe(III) compared to the other tested metal ions. The reduction–oxidation process of iron(II)/iron(III) by SGBP was also studied and the results indicated only 2.1% reduction of iron(III) into iron(II). The selectivity incorporated into silica gel phase via the immobilization of purpurogallin was intensively studied for a several binary mixtures containing iron(III)—another interfering metal ion. The determined percentage extraction values of iron(III) from these mixtures were found to be in the range of 94–100%. The potential applications of SGBP as a selective solid extractor for iron(III) from natural tap water samples and real matrices were also studied and the results revealed good percentage extraction values of iron(III) (93.5−94.9±4.6−5.3%) of the spiked iron(III) in the acidified tap water samples as well as a high preconcentration factor of 500 was also established when SGBP was used as a selective solid phase extractor and preconcentration of iron(III) from acidified soft drink samples with percentage recovery values of (98.0−97.4±4.7−5.3%) of the spiked iron(III).     

Solid-phase extraction and preconcentration of trace Pb(II) from water samples with folic acid modified silica gel

A chelating matrix prepared by immobilising folic acid on silica gel-bound amine phase was used as a new solid-phase extractant. This sorbent has been developed only for preconcentration of trace Pb(II) prior to determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions were investigated by batch and column procedures. The optimum pH value for the separation of Pb(II) on the new sorbent was 4.0. The adsorbed Pb(II) was quantitatively eluted by 2.0?cm³ of 0.5?mol?dm^?3 of HCl. Common coexisting ions did not interfere with the separation and determination of Pb(II). The maximum static adsorption capacity of the sorbent under optimum conditions was found to be 69.23?mg?g^?1 for Pb(II). The detection limit of the method defined by International Union of Pure and Applied Chemistry was 0.28?ng?cm^?3. The relative standard deviation (RSD) of the method was lower than 2.0% (n?=?8). The developed method has been validated by analysing certified reference materials and successfully applied to the determination of Pb(II) in water samples with satisfactory results.     

Kinetics of iodine-catalyzed reduction of vanadium(V) by arsenic(III)

Summary The kinetics of the iodine-catalysed reaction of vanadium(V) with arsenious acid in dilute H₂SO₄, leading to the formation of vanadium(IV) and arsenic acid, have been investigated spectrophotometrically. Plausible pathways consistent with the experimental rate law are discussed. An iodine bridged activated complex between reactant and substrate species is proposed to explain the electron mobility from arsenic to vanadium by resonance transfer. Applying other criteria, the heterolytic dissociation of the vanadium-iodine bond of the activated complex is considered rate-controlling.