Arsenic compounds, vapor pressure

Direct reaction is feasible for the IVA-VA compounds. This is surprising, since a low vapor pressure element, such as silicon, would be expected to passivate on exposure to phosphorus or arsenic. The valve metal analogy to electrochemical reactions may be invoked here fresh silicon probably diffuses rapidly through the compound, providing a continuous supply of reactant. A cold zone with a temperature of less than 500°C supplies phosphorus to the silicon, kept slightly near the 1 1 SiP melting point of 1166°Ck... 

No peaks could be detected for samples with arsenic concentrations below 100 ppm (Thurow et al., 1998), since the concentration of the analyzed compound in the head-space is to low due to low vapor pressure. Thus headspace analysis is suitable for rapid screening procedures but can not be used for trace analysis. The reproducibility of the headspace results was about 2%. 

Arsenic (CAS 7440-38-2) irritating to eyes and skin hyperplgmenta-tion, hyperkeratoses, and skin cancers have been dexribed. A general cellular poison. May cause bone marrow suppression, peripheral neuropathy, and gastrointestinal, liver, and cardiac injury. Some arsenic compounds have adverse effects on fetal development in test animals. Exposure linked to skin, respiratory tract, and liver cancer in workers (IARC 1). See also p 115. 0.01 mg/m (as As) A1 OSHACA NIOSH CA 5 mg/m (as As) Elemental forms vary In appearance. Crystals are gray. Amorphous fomes may be yellow or black. Vapor pressure is very low—about 1 mm Hg at 372°C (701°F). 

Many analytes may form volatile species with other elements in the sample, for example, halides, or be present in compounds that exhibit high-vapor pressures at relatively low temperatures (mercury, arsenic, selenium, organometallics). Such compounds may be volatilized and swept from the tube, in molecular form, prior to the atomization step. These losses can be dealt with by adding a large excess of a reagent (a modifier) to change, in situ, the thermochemical behavior of the analyte and the matrix. 

Arsenic is a gray crystalline solid that does not melt at atmospheric pressure but simply volatilizes to give a dense, malodorous yellow vapor. Its main use as an element is to harden lead-antimony alloys, for example, those in storage batteries or lead shot. Arsenic compounds are highly toxic hence, many have been used as potent herbicides and insecticides. 

Arsine is shipped as a liquefied compressed gas in steel cylinders under its own vapor pressure of 219.7 psia (1515 kPa, abs). Arsine is slightly soluble in both water and organic solvents. It reacts readily with agents such as potassium permanganate, bromine, and sodium hypochlorite to form arsenic compounds. Arsine is stable at room temperature, but begins to decompose into its elements around 446 F to 464°F (230T to 240°C). 

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