Determination alkali metals

The addition of an easily ionized substance such as cesium, which is usually not an analyte of interest in air pollution work, can reduce problems in alkali metal determination. A releasing agent, such as lanthanum, is useful for overcoming problems in analyzing for alkaline earth elements, and rare earth elements. Information on the use of these additives is given for specific cases in Table 1. 

Although the desorption of thallium occurs at relatively low emitter heating currents (20-25 mA) no interference from organic ions can be observed in the investigation of the brain tissue homogenizate. For a FD mass spectrometric investigation, however, the concentration of about 90 mg/1 thallium is high as compared to sample amounts usually required for an alkali metal determination. In order to as-... 

In 1939 Griggs " and Ells and MarshalE introduced Lundegardh s method into the United States. In 1945 Barnes et al reported on a simple filter photometer for alkali metal determinations. The Perkin-Elmer Corporation apparently was the first American corporation to market such an instrument, which was similar to that developed by Barnes. In 1948 Beckman Instruments, Inc. made a flame excitation attachment available for their spectrophotometer. 

The Birch reductions of C C double bonds with alkali metals in liquid ammonia or amines obey other rules than do the catalytic hydrogenations (D. Caine, 1976). In these reactions regio- and stereoselectivities are mainly determined by the stabilities of the intermediate carbanions. If one reduces, for example, the a, -unsaturated decalone below with lithium, a dianion is formed, whereof three different conformations (A), (B), and (C) are conceivable. Conformation (A) is the most stable, because repulsion disfavors the cis-decalin system (B) and in (C) the conjugation of the dianion is interrupted. Thus, protonation yields the trans-decalone system (G. Stork, 1964B). 

Alkali Metal Perchlorates. The anhydrous salts of the Group 1 (lA) or alkah metal perchlorates are isomorphous with one another as well as with ammonium perchlorate. Crystal stmctures have been determined by optical and x-ray methods (38). With the exception of lithium perchlorate, the compounds all exhibit dimorphism when undergoing transitions from rhombic to cubic forms at characteristic temperatures (33,34). Potassium perchlorate [7778-74-7] KCIO, the first such compound discovered, is used in pyrotechnics (qv) and has the highest percentage of oxygen (60.1%). 

Rubidium metal is commeicially available in essentially two grades, 99 + % and 99.9 + %. The main impurities ate other alkali metals. Rubidium compounds are available in a variety of grades from 99% to 99.99 + %. Manufacturers and suppliers of mbidium metal and mbidium compounds usually supply a complete certificate of analysis upon request. Analyses of metal impurities in mbidium compounds are determined by atomic absorption or inductive coupled plasma spectroscopy (icp). Other metallic impurities, such as sodium and potassium, are determined by atomic absorption or emission spectrograph. For analysis, mbidium metal is converted to a compound such as mbidium chloride. 

Fig. 11. Composition dependence of the resistivity p x) for thick films of Cbo doped with Na, K, Rb, and Cs. Points indicate where exposure to the alkali-metal source was stopped and x-ray and ultraviolet photoemission spectra were acquired to determine the concentration x. The labels indicate the known fulleride phases at 300 K. The minima in p x) occur for stoichiometries corresponding to NaQCeo, K.iCeo and Cs,.,.Cfio[ll3].

In coating fullerenes with alkali metals, the stability of the cluster seemed to be determined primarily by the electronic configuration. The units C qM and C7oMg, where M is any alkali metal, proved to be exceptionally stable cluster building blocks. Coating a fullerene with more than 7 alkali metal atoms led to an even-odd alternation in the mass spectra, inter-... 

In more recent work, Lockhart and Thompson have formed derivatives of 3 by substituting the secondary nitrogen. Substituents include CO—CH2—CH2—CH2—COOH and CH2CH2CH2 0Et. The latter compound should exhibit quite interesting binding properties for alkali metals, but binding constants for these compounds do not appear to have been determined. 

Adds.—A free acid may be at once identified by its solubility in a holution of sodium carbonate and by being reprecipitated by concentrated hydrochloric acid. If a metal has been dis-coveied in the piehminary examination, a careful examination must be made for an organic acid. As the substance is insoluble ill water the metal will probably not be an alkali metal. Boil the substance with sodium carbonate solution. The sodium salt of the acid passes into solution and the metallic carbonate IS precipitated. Filter boil the filtrate with a slight excess of nitric acid, add excess of ammonia and boil until neutral, tests may then be applied in order to identify one of the common acids and the ni.p. determined but beyond this it is impossible to carry the investigation in a limited time. 

All the alkali metals have characteristic flame colorations due to the ready excitation of the outermost electron, and this is the basis of their analytical determination by flame photometry or atomic absorption spectroscopy. The colours and principal emission (or absorption) wavelengths, X, are given below but it should be noted that these lines do not all refer to the same transition for example, the Na D-line doublet at 589.0, 589.6 nm arises from the 3s — 3p transition in Na atoms formed by reduction of Na+ in the flame, whereas the red line for lithium is associated with the short-lived species LiOH. 

The extent to whieh eharge is transferred baek from the anion towards the eation in the alkali metal halides themselves is diffieult to determine preeisely. Caleulations indieate that it is probably only a few pereent for some salts sueh as NaCl, whereas for others (e.g. Lil) it may amount to more than 0.33 e" per atom. Direet experimental evidenee on these matters is available for some other elements from teehniques sueh as Moss-bauer speetroseopy, eleetron spin resonanee speetroseopy, and neutron seattering form faetors. ... 

Phosphate, arsenate, and vanadate interfere. Borate, fluoride, and large amounts of aluminium, calcium, magnesium, and the alkali metals have no effect in the determination, but large amounts of iron (> 5 per cent) appear to produce slightly low results. 

In all cases some sensitivity to hydrogen ions remains in any potentiometric determination with these modified glass electrodes the hydrogen ion concentration of the solution must be reduced so as to be not more than 1 per cent of the concentration of the ion being determined, and in a solution containing more than one kind of alkali metal cation, some interference will be encountered. 

An example of a modem instrument of this type is the Coming Model 410 flame photometer. This model can incorporate a lineariser module which provides a direct concentration read-out for a range of clinical specimens. Flame photometers are still widely used especially for the determination of alkali metals in body fluids, but are now being replaced in clinical laboratories by ion-selective electrode procedures (see Section 15.7). 

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