Arsenic isotopes

Table 2.1 Isotopes of arsenic (Audi et al., 2003 Holden, 2007 Lindstrom, Blaauw and Fleming, 2003).15As is the only stable arsenic isotope. The possible decay modes include electron capture (EC), electron emission (P ), positron emission (P+), proton decay (p), internal transition (IT), and neutron emission (ne). Superscripts on some of the arsenic isotope mass numbers designate excited-state isomers. The first (lowest energy) excited state is designated with an m and a second excited state is designated with an n. ...

Arsenic isotope Number of neutrons Atomic mass Half-life Decay mode... 

The arsenic isotope used in the work described in Chapter 19 was As, with half-life 26.8 hours. It is made from As , which is the only isotope of ordinary arsenic, by treatment with slow neutrons ... 

In the (n, y) reaction with natural arsenic (100% As) in a nuclear reactor with a flux of 10 ncm s, samples of As with specific activity of 920mCig are obtained only. Cyclotron arsenic isotopes As are utilized in short-term biological experiments, As for medium-term experiments. 

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

Gases and vapors of volatile liquids can be introduced directly into a plasma flame for elemental analysis or for isotope ratio measurements. Some elements can be examined by first converting them chemically into volatile forms, as with the formation of hydrides of arsenic and tellurium. It is important that not too much analyte pass into the flame, as the extra material introduced into the plasma can cause it to become unstable or even to go out altogether, thereby compromising accuracy or continuity of measurement. 

Helium-3 [14762-55-1], He, has been known as a stable isotope since the middle 1930s and it was suspected that its properties were markedly different from the common isotope, helium-4. The development of nuclear fusion devices in the 1950s yielded workable quantities of pure helium-3 as a decay product from the large tritium inventory implicit in maintaining an arsenal of fusion weapons (see Deuterium AND TRITIUM) Helium-3 is one of the very few stable materials where the only practical source is nuclear transmutation. The chronology of the isolation of the other stable isotopes of the hehum-group gases has been summarized (4). 

Uranium hexafluoride [7783-81-5], UF, is an extremely corrosive, colorless, crystalline soHd, which sublimes with ease at room temperature and atmospheric pressure. The complex can be obtained by multiple routes, ie, fluorination of UF [10049-14-6] with F2, oxidation of UF with O2, or fluorination of UO [1344-58-7] by F2. The hexafluoride is monomeric in nature having an octahedral geometry. UF is soluble in H2O, CCl and other chlorinated hydrocarbons, is insoluble in CS2, and decomposes in alcohols and ethers. The importance of UF in isotopic enrichment and the subsequent apphcations of uranium metal cannot be overstated. The U.S. government has approximately 500,000 t of UF stockpiled for enrichment or quick conversion into nuclear weapons had the need arisen (57). With the change in pohtical tides and the downsizing of the nation s nuclear arsenal, debates over releasing the stockpiles for use in the production of fuel for civiUan nuclear reactors continue. 

Antimony [7440-36-0J, Sb, belongs to Group 15 (VA) of the periodic table which also includes the elements arsenic and bismuth. It is in the second long period of the table between tin and tellurium. Antimony, which may exhibit a valence of +5, +3, 0, or —3 (see Antimony compounds), is classified as a nonmetal or metalloid, although it has metallic characteristics in the trivalent state. There are two stable antimony isotopes that ate both abundant and have masses of 121 (57.25%) and 123 (42.75%). 

Arsenic [7440-38-2J, although often referred to as a metal, is classified chemically as a nonmetal or metalloid and belongs to Group 15 (VA) of the periodic table (as does antimony). The principal valences of arsenic are +3, +5, and —3. Only one stable isotope of arsenic having mass 75 (100% natural abundance) has been observed. 

Detection limits in ICPMS depend on several factors. Dilution of the sample has a lai e effect. The amount of sample that may be in solution is governed by suppression effects and tolerable levels of dissolved solids. The response curve of the mass spectrometer has a large effect. A typical response curve for an ICPMS instrument shows much greater sensitivity for elements in the middle of the mass range (around 120 amu). Isotopic distribution is an important factor. Elements with more abundant isotopes at useful masses for analysis show lower detection limits. Other factors that affect detection limits include interference (i.e., ambiguity in identification that arises because an elemental isotope has the same mass as a compound molecules that may be present in the system) and ionization potentials. Elements that are not efficiently ionized, such as arsenic, suffer from poorer detection limits. 

Arsenic and Bi (like P) each have only 1 stable isotope and this occurs with 100% abundance in... 

Wilson and Dickenson observed no exchange, over a period of three hours at 100 °C, between arsenate and arsenite ions in media ranging from aqueous acid to aqueous alkali. Martin et al have found similar results for the exchange between arsenate and thioarsenite ions in aqueous media. However, in liquid ammonia exchange occurred between ammonium arsenate and arsenic trisulphide. The isotopic method was used -... 

Tin hold the record with 10 stable isotopes. There are 19 so-called "pure elements" of which there is only one isotope. These anisotopic elements are beryllium, fluorine, sodium, aluminum, phosphorus, scandium, manganese, cobalt, arsenic, yttrium, niobium, rhodium, iodine, cesium, praseodymium, terbium, holmium, thulium, gold, and bismuth. 

Some elements do exist in only one naturally occurring stable isotope, and therefore, they are termed monoisotopic elements. Among these, fluorine ( ), sodium ( Na), phosphorus ( P) and iodine belong to the more prominent examples in organic mass spectrometry, but there are several more such as beryllium ( Be), aluminum ( Al), scandium (" Sc), manganese ( Mn), cobalt ( Co), arsenic... 

ISOTOPES There are a total of 35 isotopes of arsenic, ranging from As-60 to As-92, with half-lives spanning from a few nanoseconds to 80 days. Although some references claim there are no stable isotopes of arsenic, arsenic-75 is classed as a stable isotope that makes up 100% of arsenic found in the Earth s crust. 

Arsenic is classed as a semimetal, meaning that it is neither a metal like aluminum or lead, nor quite a nonmetal such as oxygen, sulfur, or chlorine. Arsenic s main allotrope is a silvery-gray, brittle, metal-like substance. Its other two isotopes are unstable crystalline substances. 

Gaseous sample introduction into an ICP-MS presents different problems. Owing to its extremely sensitive nature, Dean et al. [13] introduced the sample as the gaseous hydride by a flow-injection approach. This was reasonably effective because lower volumes of samples and reagents were in use. They utibzed nitric acid as a carrier stream to prevent the formation of argon chloride species in the plasma. Argon chloride has the same mass as arsenic which is mono-isotopic, and this severely bmits arsenic determination. An additional problem was that the sensitivity was extremely dependent on the purity of reagents. 

Rau, M. Rieck, D. Evans, J.W. (1987) Investigation of iron oxide reduction by TEM. Metallurgical Transactions 188 257-278 Raven, K.P. Jain, A. Loeppert, R.H. (1998) Ar-senite and arsenate adsorption on ferrihy-drite Kinetics, equilibrium, and adsorption envelopes. Environ. Sci. Techn. 32 344-349 Rea, B.A. Davis, J.A. Waychunas, G.A. (1994) Studies of the reactivity of the ferrihydrite surface by iron isotopic exchange and Moss-bauer spectroscopy. Clays Clay Min. 42 23-34... 

Silver is a white, ductile metal occurring naturally in its pure form and in ores (USEPA 1980). Silver has the highest electrical and thermal conductivity of all metals. Some silver compounds are extremely photosensitive and are stable in air and water, except for tarnishing readily when exposed to sulfur compounds (Heyl et al. 1973). Metallic silver is insoluble in water, but many silver salts, such as silver nitrate, are soluble in water to more than 1220 g/L (Table 7.3). In natural environments, silver occurs primarily in the form of the sulfide or is intimately associated with other metal sulfides, especially fhose of lead, copper, iron, and gold, which are all essentially insoluble (USEPA 1980 USPHS 1990). Silver readily forms compounds with antimony, arsenic, selenium, and tellurium (Smith and Carson 1977). Silver has two stable isotopes ( ° Ag and ° Ag) and 20 radioisotopes none of the radioisotopes of silver occurs naturally, and the radioisotope with the longest physical half-life (253 days) is "° Ag. Several compounds of silver are potential explosion hazards silver oxalate decomposes explosively when heated silver acetylide (Ag2C2) is sensitive to detonation on contact and silver azide (AgN3) detonates spontaneously under certain conditions (Smith and Carson 1977). 

One of the most famous applications in forensic science is the analysis of Napoleon s hair by ICP-MS after mineralization in concentrated nitric acid whereby an arsenic concentration about 40 times higher than normal (about 40p,gg 1) was measured (see Section 9.5). Ingested arsenic is known to be stored in sulfydryl rich tissue, like hair, nails or skin. ETV-ICP-MS combined with isotope dilution has been employed to measure thallium in human scalp hair from a person poisoned by thallium compared to control subjects, whereby several longitudinal concentration gradients for the analyzed segments (length 10 mm) were obtained.28... 

The quite different isotope effects in the dihydrogen salts of the phosphates and arsenates, shown in Fig. i, suggest that there hydrogen bonds are different in some way. It has been shown that the potential energy curve for the Ox—H 0IX bond in KH2P04 possesses two... 

---