Separation and Detection of Arsenic and Selenium Species in Environmental Samples by HPLC-ICP-MS

A method is presented for arsenic speciation analysis of an oyster sample using ion chromatography coupled with an inductively coupled plasma mass spectrometry (ICP-MS) instrument. A strong anion exchange resin was employed with a step gradient elution of 0.1 mM/0.1 M K 2 SO 4 at pH 10.2. Arsenobetaine and dimethylarsinic acid were determined following extraction based on trypsin enzymolysis with 95-100% extraction efficiency. Limits of detection in the range 0.1-0.3 mg kg m 1 of arsenic were obtained for organic arsenic species. No inorganic arsenic was detected. Validation was performed using TORT-2 as a certified reference material. Although high performance liquid chromatography (HPLC) coupled to ICP-MS is an effective method for speciation analysis it is not always necessary to obtain such a detailed picture. A simple liquid chromatographic separation technique based upon mini-column technology is presented. It was developed to obtain a fast, efficient and reliable separation of inorganic from organic, i.e. assumed toxic from non-toxic, arsenic and selenium species suitable for use as an initial screening method for environmental analysis. Two types of strong anion exchange resin were tested. Excellent separation was obtained for both min-column resins and analysis times were within 7 min. Limits of detection obtained for inorganic arsenic, organic arsenic, selenomethionine, Se IV and Se VI were 1.6, 1.8, 66, 32 and 22 µg kg m 1 , respectively.     

Arsenic Speciation in Sargassum fusiforme by Microwave-Assisted Extraction and LC-ICP-MS

Sargassum fusiforme, the common Chinese edible seaweeds, was investigated for total arsenic concentration by ICP-MS and for individual arsenic species by LC-ICP-MS. For this purpose, a microwave-assisted procedure was used for the extraction of arsenic species in freeze-dried seaweed and an analytical procedure for the sensitive and efficient speciation of the arsenic species As(III), dimethylarsinic acid, monomethyl arsonic acid, As(V), arsenobetaine and arsenocholine was optimized. Arsenic compounds were extracted from the seaweed with a methanol/water mixture; the extracts were evaporated to dryness, redissolved in water, and chromatographed on an anion exchange column. The arsenic species in Sargassum fusiforme are abundant. In some sample, the majority of arsenic compounds detected in the extracts were inorganic species, with a predominance of As (V). In addition, some significant amounts of unidentified arsenic compounds were also observed in the extracts.

     

Simultaneous determination of arsenic and antimony in environmental samples by radiochemical neutron activation analysis

A radiochemical separation procedure using an inorganic exchanger, tin dioxide (TDO), for the separation of arsenic from antimony is reported here. This separation avoids the interference of 564 keV gamma-ray of¹²²Sb in the measurement of the 559 keV gamma-ray of⁷⁶As in neutron activation analysis. Environmental samples, after neutron irradiation and digestion, are taken up in 1M HCl–0.1M HF and passed through a TDO column which selectively retains arsenic. The effluent from the TDO column, after proper conditioning, is passed through an anion exchange column for quantitative retention of antimony. The procedure has been utilized for arsenic and antimony determination in NBS Orchard Leaves and NBS Albacore Tuna.     

Etude Des Teneurs En Cuivre,Zinc, Et Arsenic Dans La Poudre De Lait Par Activation Neutronique

Abstract

Copper, zinc and arsenic have been determined in dehydrated milk powder by neutron activation analysis. Irradiation 13 of ashed milk powder in a flux of 10¹³ thermal neutrons per second per sq. cm. was followed by: elution through an anion exchange resin; solvent extraction of copper with dithizone into a chloroform phase; precipitation and subsequent redissolution of arsenic as As₂, S₃ and as a polysulfide, respectively. The determinative step involved gamma ray spectroscopy of the isotopes Zn⁶⁷, Zn⁶⁵, Cu⁶⁴ and As⁷⁶.     

High-Valent Metal–Oxo Species at the Nodes of Metal–Triazolate Frameworks: The Effects of Ligand Exchange and Two-State Reactivity for C−H Bond Activation

Through quantum-chemical calculations, we investigate a family of metal–organic frameworks (MOFs) containing triazolate linkers, M₂X₂(BBTA) (M=metal, X=bridging anion, H₂BBTA=1H,5H-benzo(1,2-d:4,5-d′)bistriazole), for their ability to form terminal metal–oxo sites and subsequently activate the C−H bond of methane. By varying the metal and bridging anion in the framework, we show how to significantly tune the reactivity of this series of MOFs. The electronic structure of the metal–oxo active site is analyzed for each combination of metal and bridging ligand, and we find that spin density localized on the oxo ligand is not an inherent requirement for low C−H activation barriers. For the Mn- and Fe-containing frameworks, a transition from ferromagnetic to antiferromagnetic coupling between the metal binding site and terminal oxo ligand during the C−H activation process can greatly reduce the kinetic barrier, a unique case of two-state reactivity without a change in the net spin multiplicity.     

Short Synthesis of Pulchellalactam

tert‐Butyl 4‐methyl‐2‐oxo‐2,5‐dihydro‐1H‐pyrrole‐1‐carboxylate 4 was synthesized by a short two‐step procedure: regioselective 1,3‐dipolar diazomethane cycloaddition to N‐Boc‐pyrrolinone 2 and thermolysis of the adduct. The compound 4 could be converted in one step into pulchellalactam.     

An Analytical Method for the Separation and Determination of As(III) and As(V) in Seepage and Acid Mine Drainage Water

To avoid changes in the original As species distribution in natural water after sampling, a method of immediate separation of As(V) by anion exchange at the sampling site was developed. The procedure consists of two steps. The total concentration of arsenic is determined in one part of the water sample acidified on site. Another part of the water samples is pressed through a column filled with an anion exchanger. The As(III) species that is not redox-stable remains in the effluent of the sorbents column and can be analyzed with conventional methods after stabilization by addition of conc. HNO₃. As(V) is sorbed by the exchanger material. The As(V) concentration can be calculated as the difference between As_sol and As(III), neglecting very low contents of methylated species. Oxidation of Fe(II) by air followed by co-precipitation of arsenic with iron hydroxide was applied in field experiments to minimize the As concentration in seepage and mining water.     

Use of a bacterial biosensor system for determining arsenic in natural waters

A procedure was developed for determining inorganic arsenic oxo anions in natural waters in concentrations of 10 μg/L and higher using a bacterial biosensor system. The most simplified procedure can be used for developing a test method.     

Development of a Multipurpose Alpha Detection Procedure for Enriched Uranium in Urine

Abstract

An anion exchange-liquid scintillation procedure for detecting enriched uranium alpha emissions in urine is described. Uranium is removed from extraneous elements by anion exchange. The uranium is eluted from the column and extracted into a liquid scintillator before being counted in a photon-electron rejecting alpha liquid scintillation spectrometer. The average recovery was 92 percent at the 0.9 dpm level.     

Simultaneous Determination of Microgram Amounts of Platinum and Palladium in Presence of Base Metals by Isolation on Anion Exchange Resin-Loaded Paper and X-Ray Spectrometry

Abstract

A procedure for simultaneous determination of microgram amounts of platinum and palladium in solutions of base metals is described. The two metals are isolated on an anion exchange resin-loaded paper disk and determined by X-ray spectrometry. The method is applied to the determination of platinum and palladium in nickel matte.     

A linear Fe–O–Fe unit in bis­(dibenzyl­dimethyl­ammonium) μ‐oxo‐bis­[tribromo­ferrate(III)]

The title compound, (C₁₆H₂₀N)₂[Fe₂Br₆O], crystallizes with one dibenzyl­dimethylammonium cation and one half of a μ‐oxo‐bis­[tribromo­ferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe—O—Fe unit. The iron(III) cations have tetra­hedral geometry, with bond angles in the range 106.8 (1)–112.2 (1)°. The ion pairs are held together by Coulombic forces and C—H⋯Br hydrogen bonds. Each Br⁻ anion forms one hydrogen bond. No C—H⋯O hydrogen bonds are found between the O atom in the Fe—O—Fe unit and surrounding counter‐cations, consistent with the linear configuration of the Fe—O—Fe unit.     

Densitometry Evaluation of the Arsenic Content of Biological Materials Using the method of Gutzeit

Abstract

By using densitometry the method of Gutzeit, previously considered to be a semiquantitative method, attains a quantitative character. The entire method, digestion of the biological materials included, is characterised by a coefficient of variation of 14%. This procedure appears to be well suited for the determination of normal values of arsenic in urine.     

Application of fast ultrasound water-bath assisted enzymatic hydrolysis--high performance liquid chromatography-inductively coupled plasma-mass spectrometry procedures for arsenic speciation in seafood materials

Enzymatic hydrolysis of seafood materials for isolating arsenic species (As(III), As(V), DMA and AsB) has been successfully performed by assisting the procedure with ultrasound energy (35 kHz) supplied by an ultrasound water-bath. The use of pepsin, as a proteolytic enzyme, under optimized operating conditions (pH 3.0, temperature 40 °C, enzyme to sample ratio of 0.3) led to an efficient assistance of the enzymatic process in a short period of time (from 4.0 to 30 min). The enzymatic extract was then subjected to a clean-up procedure based on ENVI-Carb™ solid phase extraction (SPE). An optimized anion exchange high performance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) permitted the fast separation (less than 15 min) of six different arsenic species (arsenite, As(III); arsenate, As(V); dimethylarsinic acid, DMA; and arsenobetaine, AsB; as well as monomethylarsonic acid, MMA; and arsenocholine, AsC) in a single run. Relative standard deviations (n = 11) of the over-all procedure were 7% for AsB and DMA, 11% for As(III) and 9% for MMA. HPLC–ICP-MS determinations were performed using aqueous calibrations covering arsenic concentrations of 0, 5, 10, 25, 100 and 200 μg L⁻¹ (expressed as arsenic) for As(III), As(V), MMA, DMA and AsC; and 0, 125, 250, 500, 750, 1000 and 2000 μg L⁻¹ (expressed as arsenic) for AsB. Germanium (5 μg L⁻¹) was used as an internal standard. Analytical recoveries from the anion exchange column varied from 96 to 105% (enzymatic digests spiked with low target concentrations), from 97 to 104% (enzymatic digests spiked with intermediate target concentrations), and from 98 to 103% (enzymatic digests spiked with high target concentrations). The developed method was successfully applied to two certified reference materials (CRMs), DORM-2 and BCR 627, which offer certified AsB and DMA contents, and also to different seafood samples (mollusks, white fish and cold water fish). Good agreement between certified and found AsB concentrations was achieved when analyzing both CRMs; and also, between certified and found DMA concentrations in BCR 627. In addition, the sum of the different arsenic species concentrations found in most of the analyzed samples was statistically similar to the assessed total arsenic concentrations after a total sample matrix decomposition treatment.     

Simultane Mikrobestimmung von Arsen und Vanadin in organischen Komplexverbindungen

Zusammenfassung Störendes Vanadat wurde nach der Verbrennung organischer Komplex-Verbindungen durch eine Anionenaustauscher-Mikrosäule entfernt und dadurch die Arsenbestimmung im Filtrat ermöglicht.Für die gleichzeitige Bestimmung beider Elemente war es not-wendig, die Verbrennung der Einwaage mit einer Zugabe von Natriumcarbonat durchzuführen. Das am Austauscher adsorbierte Vanadat konnte mit Schwefelsäure eluiert und im Eluat spektro-photometrisch bestimmt werden, während die Arsenbestimmung im Filtrat vorgenommen wurde. Die Abweichung vom Mittelwert betrug +0,02% As bzw. –0,13% V, die mittleren Fehler 0,10% As und 0,18% V.

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Simultaneous microdetermination of arsenic and vanadium in organic complexes

Summary In the presence of vanadium too high results for arsenic were obtained caused by coprecipitation of silver vanadate with silver arsenit following the flask combustion procedure. This error was successfully eliminated by adsorption of vanadate on an anion exchanger micro column from the neutral absorption solution prior to the determination of arsenic. Simultaneous determination of both elements was also developed including a modified combustion procedure. Addition of sodium carbonate to the sample was found neccessary for a quantitative formation of vanadate in the course of combustion. The adsorbed vanadate could effectively be eluted from the anion exchanger with sulphuric acid and after addition of hydrogen peroxide vanadium determined spectrophotometrically. In the filtrate after sucking through the exchanger, arsenic was determined as above. Deviations of the mean values and standard errors were +0.02±0,10% As and –0,13±0,18% V.

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Herrn Univ.-Prof. Dr. Hans Lieb zum 85. Geburtstag gewidmet.

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Die Autoren fühlen sich Frl. J. Firm und Frl. Z. Tran für ihre aufopfernde Arbeit zu Dank verpflichtet.     

Iron(IV) or iron(V)? Heterolytic or free radical? Oxidation pathways of a TAML activator in acetonitrile at −40 °C

The oxidation of TAML complex (1) by various oxidants is explored in MeCN with 0.2% water at ?40 °C, where the iron(V)oxo complex is stable enough for reliable spectral identification. The iron(V)oxo state is achieved using NaClO even faster than in the case of previously explored m-chloroperoxybenzoic acid. In contrast, H₂O₂ and organic peroxides (benzoyl peroxide, tert-butylperoxide, and tert-butylhydroperoxide) all convert 1 into the corresponding diiron(IV)-μ-oxo dimer (2) under the same conditions. The latter does not form when (NH₄)₂[Ce(NO₃)₆] is employed and the Fe^IV product obtained does not seem to contain an oxo moiety. In contrast to all other oxidants, the conversion of 1 by ^tBuOOH into 2 is characterized by non-conventional kinetics, and therefore this reaction was explored in some detail. The evidence is presented that this light-, O₂-, TEMPO-, and base-dependent reaction is a free radical process under the conditions used.     

Synthesis,photophysical and NMR evaluations of thiourea-based anion receptors possessing an acetamide moiety

The synthesis and photophysical evaluation of three diaryl thiourea-based anion receptors (4–6) for comparison with their urea counterparts (1–3) is outlined. These anion receptors posses an acetamide functionality on one of the aryl groups and an electron-withdrawing CF₃ group on the other. By varying the position of the acetamide group, in the o-, m- and p-positions of 4–6, respectively, the anion binding ability was both tuneable and found to be, in some cases, significantly different from that seen for the urea analogues 1–3. The binding affinities of the receptors 4–6, as well as the binding stoichiometries, were evaluated using UV–vis absorption spectroscopy in MeCN. However, these receptors were not sufficiently emissive to quantify the anion recognition using fluorescence. The results confirmed strong binding of these receptors to anions such as fluoride, acetate, phosphate, pyrophosphate and chloride. Nevertheless, the overall results obtained did not conform to the anticipated trends seen for 1–3, which is most likely due to the enhanced binding affinity of the thiourea analogues 4–6. The binding interactions were also investigated by using ¹H NMR which confirmed that these receptors interacted with the anions in a stepwise manner, where the primary anion binding interaction occurred at the thiourea side, which led to an activation of the acetamide moiety towards the second anion binding interaction, an example of an allosteric activation mode.     

Polarographic and Voltammetric Assays of Sulfonamides as α‐Oxo‐γ‐Butyrolactone Arylhydrazones

Abstract

2‐Acetylbutyrolactone was characterized as a novel reagent of analytical potential in polarographic and voltammetric analyses. It forms α‐oxo‐γ‐butyrolactone arylhydrazones through Japp‐Klingemann coupling reaction with primary arylamines. α‐Oxo‐γ‐butyrolactone arylhydrazones possess an electro‐active site (azomethine center) that displays a cathodic activity at the mercury electrode. The protonated azomethine center of α‐oxo‐γ‐butyrolactone arylhydrazones is reduced by 2e/2H⁺ reaction to the hydrazo form. The differential pulse polarographic behavior of α‐oxo‐γ‐butyrolactone arylhydrazones was investigated in aqueous media ranging from pH 2 to 10.5. In aqueous acidic solution, α‐oxo‐γ‐butyrolactone arylhydrazones were shown to adsorb on a hanging mercury drop electrode and to be amenable to determination by adsorptive stripping voltammetry. Procedures for applying the polarographic and voltammetric methods to determination of sulfadiazine and sulfamethoxazole in pharmaceutical preparations have been developed. An analogous study on sulfas‐azo derivatives of ethyl acetoacetate was also considered. Furthermore, the differential pulse voltammetric method was adopted for determination of sulfamethoxazole in spiked plasma and urine samples. The recoveries turned out to be satisfactory, showing relative standard deviations from 2.4 to 4.6%.     

Synthesis of Pyrano‐ and Pyrido‐Anellated Pyranosides as Precursors for Nucleoside Analogues

The push‐pull activated methyl (3Z)‐4,6‐O‐benzylidene‐3‐[(methylthio)methylene]‐3‐deoxy‐α‐D‐erythro‐hexopyranosid‐2‐ulose (1) reacted with dialkyl malonate in the presence of potassium carbonate to give the alkyl (2R,4aR,6S,10bS)‐4a,6,8,10b‐tetrahydro‐6‐methoxy‐8‐oxo‐2‐phenyl‐4H‐pyrano[3′,2′:4,5]pyrano[3,2‐d][1,3]dioxine‐9‐carboxylates 2 and 3. Treatment of 1 with 3‐oxo‐N‐phenyl‐butyramide, N‐(4‐methoxy‐phenyl)‐3‐oxo‐butyramide, and 3‐oxo‐N‐o‐tolyl‐butyramide, respectively, in the presence of potassium carbonate and 18‐crown‐6 yielded the (2R,4aR,6S,10bS)‐9‐acetyl‐7‐aryl‐4,4a,7,10b‐tetrahydro‐6‐methoxy‐2‐phenyl[1,3]dioxino‐[4′,5′:5,6]pyrano[3,4‐b]pyridin‐8(6H)‐ones 4–6. (2R,4aR,6S,10bS)‐4,4a,8,10b‐Tetrahydro‐6‐methoxy‐8‐oxo‐2‐phenyl‐4H‐pyrano[3′,2′:4,5]pyrano[3,2‐d][1,3]dioxine‐9‐carboxamide (7) was prepared by anellation reactions of 1 either with malononitrile or with cyanoacetamide.     

HPLC Urinary Organic Acid Profiling: Role of the Ultraviolet and Amperometric Detectors

Abstract

The profiling of urinary organic acids is an important aspect of the diagnosis of inborn metabolic disorders. The carboxylic acids of interest may contain additional functional moities such as phenyl, hydroxyl, oxo, etc. The state-of-the-art method of organic acid analysis is by GC/MS. Prior to GC/MS analysis, the carboxylic acids must be isolated from urine by extraction or ion exchange chromatography and made volatile by derivatization. This is a lengthy procedure that does not lend itself to rapid analysis. We have developed a rapid procedure for the profiling of urinary α, B-unsaturated, aromatic and α-ketocarboxylic acids.

Urine containing an internal standard, 3-hydroxy-4-methoxy-benzyl alcohol, is filtered through a 0.3 um Millipore filter and injected on to an HPX-87 organic acid HPLC column (Bio-Rad). The mobile phase, 4.5 mN H₂SO₄, is passed through the column at 0.8 ml/min. Detection is effected by an UV detector at 200 nm in series but upstream from an electrochemical detector with a glassy carbon working electrode at +1.15V vs. an Ag/AgCl reference electrode. At this electrode potential, phenolic, methoxyphenyl, eneolic and α-ketocarboxylic acids are oxidized and can be electrochemically detected with a glassy carbon electrode.     

Determination of Arsenic in Organic Compounds and Other Matrices by Flame Emission Spectrometry

Abstract

A direct and simple method for arsenic in organic compounds involves merely dissolution of the sample in an organic solvent, such as benzene, cyclohexane, or methyl isobutyl ketone, and direct aspiration into a fuel-rich acetylene-oxygen flame. The arsenic line at 2350 Å is used; the detection limit is 2.2 ü/ml. From iron and copper matrices arsenic is isolated by extraction from a solution 9 M in HCI and 0.25 M in KI with benzene.