Trace elements, arsenic volatilization

Frankenberger W.T. Jr. Effects of trace elements on arsenic volatilization. Soil Bio Biochem 1997 30 269-274. 

Figure 9.8. Biological and chemical transformations of arsenic in the soil. Broken arrows denote the loss of volatile forms of As to the atmosphere or the air-filled pores of the soi. (Modified from B. E. Davies. 1980. Trace element pollution. In B. E. Davies (ed.). Applied Soil Trace Elements. New York Wiley.)...

The advantages of microwave dissolution include fester digestion that results from the high temperature and pressure attained inside the sealed containers. The use of closed vessels also makes it possible to eliminate uncontrolled trace element losses of volatile species that are present in a sample or that are formed during sample dissolution. It is well known that significant amounts of elements such as arsenic, boron, chromium, mercury, antimony, selenium, and tin are lost at relative mild temperature with some open vessel acid dissolution procedures [8,9]. Another advantage of microwave dissolution is to have better control of potential contamination in blank as compared to open vessel procedures. This is due to less contamination from laboratory environment, unclean containers, and smaller quantity of reagents used. 

The presence of heavy metals and other elements may inhibit or enhance microbiological transformations of arsenic in soil systems. It was observed that presence of phosphate and selenate causes inhibition of methylated evolution of arsenic (5,46,56). Frankenberger (57) studied the effect of 21 trace elements for their activation or inhibition on methylated arsine production by a Penicillium sp. from MMAA. Metals and metalloids at an elemental concentration of 0, 0.1, 1, 10, 100, and 1000 pM were tested for their influence on arsenic volatilization by the Penicillium sp. The effect of trace elements varied considerably depending on the speciation and concentration. At the lower elemental concentrations (0.1 and 1 pM), the metals and metalloids that stimulated arsenic volatilization were... 

Table 3 Effect of Trace Elements on Arsenic Volatilization (ng ml )...

Trace element Oxidation state Arsenic volatilized at different concentrations (pM) of added trace elements ... 

Dming the oxidation process, the analyte(s) will behave in one or more of a munber of ways. Ideally, they will quantitatively remain in the residue (ash) arising from the oxidation, and in a form in which they can be readily recovered, generally by a simple dissolution of the ash in an appropriate acid. Fortunately, for the usefulness of the method, this is the case for most analytes and samples. In some cases, a part (or the total) of the analyte may be converted to a volatile form that may escape from the vessel (i.e., volatilization losses) or may be combined with the vessel smiace or with some components of the inorganic residue remaining after oxidation (i.e., retention losses). In practical trace element analysis, the most often reported volatilization losses pertain mainly to mercury, arsenic, and selenimn. 

Estimation of Selenium in Sulphide Minerals.s—In various sulphite-cellulose manufactories difficulties have occurred which have been traced to the presence of selenium in the pyrites used for burning. Part of the selenium remains in the burnt pyrites and part volatilises with the sulphur dioxide. 20 to 30 grams of pyrites are dissolved in hydrochloric acid (dens.=1-19) and potassium chlorate. Zinc is added to reduce the iron to the ferrous condition more hydrochloric acid is then added, the solution boiled and stannous chloride added to precipitate selenium. Since the selenium may contain arsenic, it is collected on an asbestos filter, dissolved in potassium cyanide and reprecipitated using hydrogen chloride and sulphur dioxide. The element may then be estimated by the iodometric method described below. In order to determine the relative proportion of volatile to non-volatile selenium, the pyrites may be roasted in a current of oxygen. After this treatment the contents of the tube are dissolved in warm potassium cyanide and the selenium reprecipitated and estimated in the ordinary way. 

For trace analysis, the main ceramic elements of interest are Zn, Pb, Cu, Bi, Sb, Sn, Ag, As, Mn, Cr, Se, and Hg. Many of these are environmentally important. In certain cases the detection limits of flame AAS are inadequate, so that hydride generation for antimony, selenium, arsenic and bismuth, cold vapor for mercury, and graphite furnace AAS for lead and cadmium are required. A variation of AAS is atomic fluorescence, and this is used to achieve the detection limits needed for Hg and Se in environmental samples. Microwave digestion techniques for sample preparation are becoming more common, where, unlike fusion, there is no risk of loss of volatile elements from unfired samples and fewer reagents are... 

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