Arsenic-containing compounds

Arsenic present only in traces (in any form) can be detected by reducing it to arsine and then applying tests for the latter. In Marsh s test, dilute sulphuric acid is added dropwise through a thistle funnel to some arsenic-free zinc in a flask hydrogen is evolved and led out of the flask by a horizontal delivery tube. The arsenic-containing compound is then added to the zinc-acid solution, and the delivery tube heated in the middle. If arsenic is present, it is reduced to arsine by the zinc-acid reaction, for example ... 

Trimethyl arsine [593-88-4] C H As, has been identified as the toxic volatile arsenical, once known as "Gosio gas," produced by the reaction of certain molds that grow on wallpaper paste and react with inorganic arsenic compounds present in the paper. A number of microorganisms can methylate arsenic trioxide and other arsenic-containing compounds to yield trimethylarsine. These microorganisms include Scopulariopsis brevicaulis Candida humicola and Gliocladium roseum (72). 

In chemical combination, arsenic can exist in oxidation state III or V and can have a coordination number of 3, 4, 5, or 6. In marine samples, arsenic is mainly found in the V oxidation state, although, usually as a consequence of biological factors, arsenic (III) compounds can also occur and may at times be predominant. The properties and analysis of the various arsenic-containing compounds of significance in marine arsenic research are briefly discussed, and information is provided on their synthesis. For ease of reference, the arsenic compounds frequently mentioned by name (or abbreviation/acronym) are listed in Table IV together with their structure numbers. 

Names, Abbreviations, and Structures of Some Marine Arsenic-Containing Compounds... 

Attempts have been made to use this difference in reactivity to distinguish between the two arsenic-containing compounds in marine samples. Although some success was achieved on synthetic materials, the results from marine samples (47) have been misleading and have been questioned (32). 

Clearly there is much to be learned from further examination of arsenic levels in seawater and porewaters. However, low concentrations and analytical difficulties presented by the salt matrix continue to complicate these analyses (33, 85). Techniques such as HPLC/ICP-MS suffer from interference by the molecular ion 40Ar35Cl +, formed by combination of the plasma gas and chloride ion, with the monoisotopic 75As+. Techniques to separate the arsenic compounds from the salt matrix before HPLC/ICP-MS have not been fully investigated because they may result in fractionation of the compounds and loss of speciation information. Nevertheless, methods to establish the presence or otherwise in seawater of some of the arsenic-containing compounds important in other marine compartments is worth pursuing. 

Arsenic-Containing Compounds from Marine Algae... 

In September 1966 The New York Times published a report that cacodylic acid, an organic arsenic containing compound, was also being used in Vietnam.49 Cacodylic acid was a defoliant that was also toxic to man. According to the Merck Index, cacodylic acid was a dimethylarsenic acid containing 54.29 per cent arsenic, and was extremely poisonous.50 Seventy grams would kill the average 150-lb man if administered subcutaneously. 

As we mentioned earlier in Chafer 1, the first chemicals used in weed control were the inorganics. Until the 1960s arsenic-containing compounds were commonly used and therefore we will start with them. 

Like most other organic arsenic containing compounds, the arsonic acids are more or less susceptible to adsorption, and because the influence of adsorption on the half-wave potential is dependent on substituents, concentration and the presence of surfactants, it is... 

In order to reach high sensitivity and sufficient detection limits for the determination of the arsenic species the arsenic emission lines at 189.04, 193.7, 200.33, and 234.94 nm were studied using triphenylarsine as reference substance. The most sensitive arsenic line at, 193.7 nm is interfered by a strong carbon line and thus the wavelength at 189 nm has been used for arsenic identification according to Mothes and Wennrich (1997). A total of 24 arsenic containing compounds have been detected in the dichlor-omethane extracts and thermal desorption investigation, respectively (Thurow et al., 1999). The presence of arsenic was confirmed by the five characteristic lines between 180 and 210 nm (see Fig. 13). 

A total of 22 arsenic containing compounds could be identified in the soil and plant samples using combination of mass spectrometric and atomic emission spectroscopic detection (Fig. 16). The soil samples showed a variety of arsenic species with Clark I, triphenylarsine and bis(diphenylarsine)oxide (which is a typical breakdown product of Clark I) as the main contaminants. The identification of numerous compounds was possible by a combination of mass spectrometric information and elemental compositions resulting from GC/AES investigations. 

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