Element chloride, volatility

If one does not have the possibility of using different sources for different elements, one may feed the source with compounds more volatile than the elements. Chlorides, fluorides, and oxides, in particular, are useful feed materials. Unfortunately, some compounds, which are otherwise suitable, tend to undergo thermal decomposition in the source and therefore have to be eliminated. Others, such as some chlorides, are extremely sensitive to water and hence converted under normal experimental conditions into their non-volatile oxides. To overcome this difficulty, the CCI4 method was developed. With it the desired element is stored as an oxide in a rather hot zone near the inlet of the ion source. By passing CCI4 over the oxide an in situ chlorination takes place and the resulting chloride is immediately swept in-... 

A number of elements form volatile chlorides that are partially or completely lost from hot hydrochloric acid solutions. Among these are the chlorides of tin(IV), germanium(IV), antimony(III), arsenic(III), and mercury(II). The oxychlorides of selenium and tellurium also volatilize to some extent from hot hydrochloric acid. The presence of chloride ion in hot concentrated sulfuric or perchloric acid solutions can cau.se volatilization losses of bismuth, manganese, molybdenum, thallium, vanadium, and chromium. 

These measurements are summarized in Table II. In general, temperature has little effect on retention. These results and earlier observations indicating complete retention of metals in compounds such as arseneous chloride and metalloporphyrins (5) are believed to be caused by competition between volatilization and oxidation to less volatile compounds. Unlike the other elements studied, the highest valence oxide of osmium, 0s04, is the most volatile. Therefore, this element is volatilized in the plasma oxidation process. 

The gas phase interferences are obviously limited to those species which can be transferred into the vapor phase under these conditions, i.e., the hydride-forming elements and mercury. And if tin(II) chloride is used for the determination of mercury, no other element is volatilized so that no such interferences can occur. The mumal interferences of hydride-forming elements, however, may be quite severe, particularly in batch systems [36]. FI systems have been shown one more time to be superior also in this case as these mutual interferences are one to two orders of magnitude less pronounced compared to batch systems [37]. They should therefore be no problem in the analysis of body fluids or tissues, even in the case of a severe intoxication. 

There are a several examples of the conversion of a solid with a gaseous reactant into a gaseous product, such as the gasification and the burning of solid fuels, the conversion of some elements into volatile oxides, chlorides or oxychlorides, and the reductive chlorination of metal oxides to volatile chlorides, etc. 

A century ago, Mendeltef used his new periodic table to predict the properties of ekasilicon , later identified as germanium. Some of the predicted properties were metallic character and high m.p. for the element formation of an oxide MOj and of a volatile chloride MCI4. 

The general characteristics of all these elements generally preclude their extraction by any method involving aqueous solution. For the lighter, less volatile metals (Li, Na, Be, Mg, Ca) electrolysis of a fused salt (usually the chloride), or of a mixture of salts, is used. The heavier, more volatile metals in each group can all be similarly obtained by electrolysis, but it is usually more convenient to take advantage of their volatility and obtain them from their oxides or chlorides by displacement, i.e. by general reactions such as... 

When an element has more than one oxidation state the lower halides tend to be ionic whilst the higher ones are covalent—the anhydrous chlorides of lead are a good example, for whilst leadfll) chloride, PbCl2, is a white non-volatile solid, soluble in water without hydrolysis, leadflV) chloride, PbC, is a liquid at room temperature (p. 200) and is immediately hydrolysed. This change of bonding with oxidation state follows from the rules given on p.49... 

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. 

The iodides of the alkaU metals and those of the heavier alkaline earths are resistant to oxygen on heating, but most others can be roasted to oxide in air and oxygen. The vapors of the most volatile iodides, such as those of aluminum and titanium(II) actually bum in air. The iodides resemble the sulfides in this respect, with the important difference that the iodine is volatilized, not as an oxide, but as the free element, which can be recovered as such. Chlorine and bromine readily displace iodine from the iodides, converting them to the corresponding chlorides and bromides. 

Depending on the extraction method and the source of Rb and Cs, the elements are obtained in industry as chlorides, nitrates and carbonates. Methods of preparing and purifying all of the alkali metals are described with examples. Methods for Rb and Cs are governed by the relative ease of reduction of their compounds, the volatility of the extracted metal and the extreme chemical reactivity of these heavier alkali metals toward air and moisture. 

The last reaction is the most favored of these three. The actual occurrence of the reactions with elemental phosphorus or phosphorous trichloride as products has been explained to be due to kinetic reasons. The thorium present in the ore volatilizes in the form of thorium tetrachloride (ThCl4) vapor other metallic impurities such as iron, chromium, aluminum, and titanium also form chlorides and vaporize. The product obtained after chlorination at 900 °C is virtually free from thorium chloride and phosphorous compounds, and also from the metals iron, aluminum, chromium, and titanium. 

A number of workers have described methods for the determination of mercury in which the mercury is first reduced to the element or collected as the sulfide on a cadmium sulfide pad. It is then volatilized into a chamber for measurement. These techniques are extremely sensitive. Thillez108) recently described a procedure for urinary mercury in which the mercury is collected on platinum and then volatilized into an air stream. Rathje109) treated 2 ml of urine with 5 ml of nitric acid for 3 min, diluted to 50 ml, and added stannuous chloride to reduce the mercury to the element. A drop of Antifoam 60 was added and nitrogen was blown through the solution to carry the mercury vapor into a quartz end cell where it is measured. Six nanograms of mercury can be detected. Willis 93) employed more conventional methods to determine 0.04 ppm of mercury in urine by extracting it with APDC into methyl-n-amyl ketone. Berman n°) extracted mercury with APDC into MIBK to determine 0.01 ppm. 

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