Marine samples arsenic

Marine biological material, radioactivity of, 3 315-316 Marine samples arsenic in, 44 148-151 compounds found, 44 151-162 occurrence and distribution, 44 149-151, 162-169... 

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. 

All four dissolution procedures studied were found to be suitable for arsenic determinations in biological marine samples, but only one (potassium hydroxide fusion) yielded accurate results for antimony in marine sediments and only two (sodium hydroxide fusion or a nitricperchloric-hydrofluoric acid digestion in sealed Teflon vessels) were appropriate for determination of selenium in marine sediments. Thus, the development of a single procedure for the simultaneous determination of arsenic, antimony and selenium (and perhaps other hydride-forming elements) in marine materials by hydride generation inductively coupled plasma atomic emission spectrometry requires careful consideration not only of the oxidation-reduction chemistry of these elements and its influence on the hydride generation process but also of the chemistry of dissolution of these elements. 

Sedimentation equilibrium technique, 19 256 Sedimentation velocity technique, 19 256 Sediments, arsenic in marine samples, 44 149, 162-164, 169, 181 [Se U ] cations, 35 297-298 Selective vaporization, for preparation of actinide metals, 31 12-13, 26 Selenide, production, 38 82 Selenium... 

Occurrence and Distribution of Arsenic Compounds in Marine Samples... 

Although there had been earlier reports (1-3) of the presence of arsenic in marine samples, the first comprehensive study was presented by Jones (4) in 1922. He examined marine algae collected from British coastal waters, reporting concentrations of arsenic and information on its extraction with water and ethanol. He referred to the arsenic as organic arsenic and, perhaps somewhat mischievously, remarked that the reputed medicinal properties of some algae may be due to their organic arsenic content. 

In work related to the human toxicology of arsenic, Cox (5) noted that within 24 hours after a person eats fish, arsenic can be measured in the urine at levels normally indicative of chronic arsenic poisoning. The subsequent study of Chapman (6) in 1926 established the occurrence of high levels of arsenic in a wide range of marine organisms. Arsenic concentrations in seawater were also reported at this time (7). Over the ensuing years there followed only infrequent reports (e.g., 8) on arsenic in marine samples until the late 1960s. Renewed interest... 

Arsenic compounds with one to four methyl groups attached to the arsenic atom are common constituents of marine samples. The relevant species are monomethylarsonic acid (MMA) (3), dimethylarsinic acid (DMA) (4), trimethylarsine oxide (TMAO) (5), and tetramethylarson-ium ion (TeMA) (6). Of these, MMA and DMA are readily separated... 

The compounds MMA, DMA, and TMAO are reduced in acidic aqueous media by borohydride solutions to methylarsine (MeAsH2, bp 2°C), dimethylarsine (Me2AsH, bp 35°C), and trimethylarsine (Me3As, bp 55°C), respectively. These products are useful derivatives for speciation analysis of arsenic because they are readily separated from complex sample matrices and may be further separated from each other by distillation (41) or by gas chromatography (42) prior to their determination by element-specific detectors. Consequently, arsine generation techniques are the most commonly used methods for determining MMA, DMA, and TMAO in marine samples. 

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). 

A number of arsenic-containing ribosides, also referred to here simply as arsenosugars, occur in marine samples. Most of the arsenosugars are dimethylarsinoylribosides (Fig. 2, compounds 9 to 25). This group of compounds was unknown prior to 1981, when 9 and 12 were isolated from a brown alga (55). Structures for the two compounds were origi-... 

Fig. 3. Typical separation of four arsenosugars and DMA by HPLC/ICP-MS using an ODS reversed-phase column at pH 3.2 under conditions described in Ref. 60. The sensitivity and specificity of the detector allows the determination of arsenosugars and other arsenic compounds to be conducted on dilute aqueous extracts of the marine samples.

Karthikeyan, S. and S. Hirata. 2004. Ion chromatography-inductively coupled plasma mass spectrometry determination of arsenic species in marine samples. Appl. Organomet. Chem. 18 323-330. 

W. A. Maher, A decomposition procedure for the determination of arsenic in marine samples, Talanta, 30 (1983), 534-536. 

The concentrations of the three arsenicals (75-77) were determined in 37 marine organisms comprising algae, crustaceans, bivalves, fish and mammals by high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) [170]. All three organoarsenics, which occurred at pg/kg concentrations, were detected in 25, 23 and 17 of the 37 samples analyzed, respectively. The limits of detection were 2-3 pg/kg dry mass. The data illustrate that all three compounds are common minor constituents in practically all marine samples. 

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