Synthesis and isolation of methyl bismuth cysteine and its definitive identification by high resolution mass spectrometry

After the synthesis and isolation of methylated bismuth cysteine, its initial identification by IR-spectroscopy was performed, whereas for definitive identification, high resolution mass spectrometry (ESI-TOF-MS and LTQ Orbitrap) was carried out.     

A novel device layout for tunneling spectroscopy of low-dimensional electron systems

We report tunneling spectroscopic investigations on a barrier separated double-electron-layer system using a novel selective depletion scheme based on self-aligned side gates. We show that the side gate technique is also suitable to impose a tunable lateral confinement on a narrow channel. From the study of tunneling processes on a single-wire device we conclude that the energetic spacing of the one-dimensional subbands can be varied from effectively zero to up to 6 meV. A simple electrostatic model confirms the order of magnitude of the measured one-dimensional level spacing.     

Comparative phytotoxicity of methylated and inorganic arsenic- and antimony species to Lemna minor, Wolffia arrhiza and Selenastrum capricornutum

The alkylation of metalloids through the transfer of methyl groups is an important factor in the biogeochemical cycling of elements like arsenic and antimony. In the environment, many different organic and inorganic forms of these elements can therefore be found in soils, sediments or organisms. Studies that compare the ecotoxicity of these different chemical species however are rare. Therefore, this study aimed to generate toxicity data on two scarcely studied organic compounds of arsenic and antimony, as well as to compare their toxicity to the inorganic species, which are studied so far to a higher extent, in order to improve the environmental effect assessment of these elements. To this purpose, bioassays were performed in which three different aquatic organisms (the floating water plants Lemna minor and Wolffia arrhiza and the green alga Selenastrum capricornutum) were exposed to a concentration series of 3 different arsenic species (sodium arsenite — As(III), sodium arsenate — As(V), and monomethylarsonous diiodide — MMAs(III)) and three different antimony species (antimony potassium tartrate hydrate — Sb(III), potassium hexahydroxoantimonate — Sb(V), trimethylantimony(V) bromide — TMSb(V). The observed effect concentrations demonstrated that the inorganic (III)- and (V)-valent species of arsenic were clearly more toxic than the corresponding antimony species. The highest overall toxicity has been shown by MMAs(III) followed by the inorganic As(III). The highest toxicity of the three tested antimony species has been observed for TMSb(V). The observed differences in effect levels stress the importance once more that speciation must not be ignored in toxicity studies.     

Digestion of organic components in waste materials by high pressure ashing with infrared heating

In respect of complete digestion of organic waste materials, a relevant potent digestion technique was developed, and a prototype of a high pressure ashing device with infrared heating (IR-HP-asher) was built. The apparatus consists of six quartz digestion vessels inside a steel autoclave. The performance of the IR-HP-asher was tested for pure organic substances, for representative wastes from the recycling industry, and for several biological samples. In all cases, complete digestion could be attained within 90 min as well as complete recovery of metal(loid)s present in the sample. Concerning the completeness of digestion and absence of analyte loss, the IR-HP-asher was found to be superior to two conventional microwave digesters also tested.     

Development and application of liquid and gas-chromatographic speciation techniques with element specific (ICP-MS) detection to the study of anaerobic arsenic metabolism

Following the observation of volatile hydride and methylated arsenic species in the gases released from sewage treatment facilities and municipal landfills, we have developed a method for investigating the production of such gases by an anaerobic organism. Here we report the application of high performance ion chromatography (HPIC), hydride generation gas chromatography (HG-GC), and purge and trap gas chromatography (PT-GC), coupled with inductively-coupled plasma mass spectrometry (ICP-MS) to study the formation of ionic and volatile arsenic compounds produced in a batch culture of the anaerobic methanogen Methanobacterium formicicum. In this time course experiment we observed arsenite, mono- and dimethylated arsenic acid, arsine, mono-, di- and trimethylarsine, as well as a currently unknown volatile arsenic species.     

Speciation of metals and metalloids in sediments with LTGC/ICP-MS

Low temperature GC on-line coupled with an ICP/MS has been used as analytical device to detect organometallic and -metalloid compounds from various sediments of rivers and harbours in West Germany. The different species have been volatilized by derivatization with NaBH(4) and cryofocussed in a trap. Different alkylated species of As, Sn and Sb have been identified, while only methylated compounds of the elements Ge, Se, Te, Hg and Bi could be detected.     

Trace Element Speciation in Soils and Sediments Using Sequential Chemical Extraction Methods

Abstract

Several commonly used sequential chemical extraction procedures of heavy metals in soils and sediments are compared, and their advantages and disadvantages are discussed focusing on selected case studies. In particular, problems caused by handling of anoxic samples, and of specific phases (e.g. organic fractions and sulfides) are addressed.

Eventually, recommendations for the improvement of extraction selectivity as well as the reduction of readsorption effects are given.     

Speciation of alkylated metals and metalloids in the environment

The analytical methodology for speciation of metals and metalloids associated with alkyl groups and biomacromolecules is critically reviewed. Alkylated metals and metalloids are not only known to be produced by microbial methylation within most anaerobic compartments in the environment, but also in the course of enzymatic transformations during human metabolism. Because of the toxicological relevance of these compounds present in trace to ultratrace concentrations, firm species identification and exact quantification are essential. While many instrumental techniques coupling chromatography (GC, HPLC, CE, GE) with plasma mass spectrometry (ICP-MS) are available for quantification, methods used for structural identification often suffer from inadequate sensitivity (EI-MS, ESI-MS, MALDI-MS, FT-ICRMS). Other problems encountered are sample derivatisation artefacts, lack of suitable standards for quantification, lack of equilibrium between spikes and sample, and the integrity of metal–protein association during separation, in particular during SDS-PAGE. Selected application examples with respect to mercury and arsenic speciation will be discussed critically.      

Derivatization of organometal(loid) species by sodium borohydride problems and solutions.

Like other derivatization techniques, hydride generation is a chemical reaction that produces side-reactions leading to analytical problems. Demethylation of dimethylarsinic acid was observed to be dependent upon the pH level of the hydride generation reaction mixture. If the reaction mixture was acidic, then in addition to (CH3)2AsH, the monomethyl arsenic hydride [(CH3)AsH2] could be detected. Demethylation and also the formation of an unidentified arsenic species were noted when trimethyl arsonic oxide was used as derivatization educt. All of these effects depend on the pH level of the hydride generation mixture. We observed significant levels of organometal(loid) species of elements such as Ge, As, Sn, Sb, Hg and Bi in blank hydride generation mixtures. The organometal(loid) contamination was irreproducible even during I day using a single solution of sodium borohydride in deionized water. We concluded that the organometal(loid) contamination arises directly from the derivatization agent, sodium borohydride, itself. Use of helium purging and various adsorptive materials to decontaminate the sodium borohydride solution prior to analysis did not result in a significant decrease in organometal(loid) contamination levels. Use of a palladium-cluster stabilised with 1,10-phenanthrolin as alternative hydride generation derivatization agent was not found to be suitable, since reaction yields were poor and transmethylation reactions were noted.