Caesium, determination

As iron and cobalt both interfere with the determination of caesium, using the 852.1 nm caesium line, these elements were removed in a preliminary separation and then caesium determined. 

A reference solution is used to compensate for the influence of the potassium. It consists of a precipitate of a quantity of potassium, prepared in the same way, corresponding to the content of potassium ions in the quantity of water used for the rubidium and caesium determination. This generally entails no particular difficulty since a determination of potassium precedes the determination of Rb and Cs in the course of w.ater analysis. Experience shows that the potassium content in water hardly ever exceeds 300 mg/1. Consequently, the method has been adapted to a constant potassium content of 200 mg/1, which may be achieved by adding potassium chloride if the content of the natural water sample is lower. 

All the cations of Group I produce a characteristic colour in a flame (lithium, red sodium, yellow potassium, violet rubidium, dark red caesium, blue). The test may be applied quantitatively by atomising an aqueous solution containing Group I cations into a flame and determining the intensities of emission over the visible spectrum with a spectrophotometer Jlame photometry). 

The chemical identities of the fission products determine their subsequent redistribution, those elements which are in the gaseous state at the temperature of the operation migrating to the cooler exterior of the fuel rods, and die less voltile elements undergoing incorporation in the fuel rod in solid solution. Thus caesium and iodine migrate to the gas fill which sunounds the fuel rod, and elements such as the rare earths and zirconium are accommodated in solid solution in UO2 without significant migration along the fuel rod radius. Strontium and barium oxidize to form separate islands which can be seen under the microscope. 

Ammonium may be determined by predpitation with sodium tetraphenylborate as the sparingly soluble ammonium tetraphenylborate NH4[B(C6H5)4], using a similar procedure to that described for potassium it is dried at 100°C, For further details of the reagent, including interferences, notably potassium, rubidium, and caesium, see Section 11.38,... 

Many other heterogeneous electrodes have been developed based on, e.g., calcium oxalate or stearate in paraffin, barium sulphate in paraffin or silicone-rubber, bismuth phosphate or iron(III) phosphate in silicone-rubber, caesium dodecamolybdophosphate in silicone-rubber and amminenickel nitrate in phenol-formaldehyde resin39 these permit the determination, respectively, of Ca and oxalate, Ba and sulphate, Bi or Fe(HI) and phosphate, Cs, Ni and nitrate, etc. 

Atomic absorption spectrometry has been used to determine caesium in seawater. The method uses preliminary chromatographic separation on a strong cation exchange resin, ammonium hexcyanocobalt ferrate, followed by electrothermal atomic absorption spectrometry. The procedure is convenient, versatile, and reliable, although decomposition products from the exchanger, namely iron and cobalt, can cause interference. 

Shen and Ii [149] extracted caesium (and rubidium) from brine samples with 4-tert-butyl-2-(a methyl-benzyl) phenol prior to atomic absorption spec-trometric determination of the metal. 

Vandecasteele et al. [745] studied signal suppression in ICP-MS of beryllium, aluminium, zinc, rubidium, indium, and lead in multielement solutions, and in the presence of increasing amounts of sodium chloride (up to 9 g/1). The suppression effects were the same for all of the analyte elements under consideration, and it was therefore possible to use one particular element, 115indium, as an internal standard to correct for the suppressive matrix effect, which significantly improved experimental precision. To study the causes of matrix effect, 0.154 M solutions of ammonium chloride, sodium chloride, and caesium chloride were compared. Ammonium chloride exhibited the least suppressive effect, and caesium chloride the most. The results had implications for trace element determinations in seawater (35 g sodium chloride per litre). 

A further method for the determination of caesium isotopes in saline waters [60] is based on the high selectivity of ammonium cobalt ferrocyanide for caesium. The sample (100-500 ml) is made 1 M in hydrochloric acid and 0.5 M in hydrofluoric acid, then stirred for 5-10 min with 100 mg of the ferrocyanide. When the material has settled, it is collected on a filter (pore size 0.45 im), washed with water, drained dried under an infrared lamp, covered with plastic film and / -counted for 137caesium. If 131caesium is also present, the y-spectrometric method of Yamamoto [61] must be used. Caesium can be determined at levels down to 10 pCi/1. 

Riel [67] studied in situ extraction combined with y-ray spectrometry in an underwater probe for the determination caesium and chromium in seawater. 

For XV) complexes have been obtained with molecular ratios 1 1 for potassium and sodium salts, 2 3 for rubidium and ammonium thiocyanate, and 1 2 for caesium thiocyanate. The rubidium and ammonium thiocyanate compounds are isomorphous, and the structure of the former was the first of this type to be determined 92). In the crystal there is a 1 1 complex and a molecule of crystallisation of un-complexed (XT). The metal is coordinated by six coplanar oxygen atoms... 

H. Topsoe found the refractive indices of crystals of potassium bromide to be 1 5546 for the C-line 1"5593 for the D-line 15715 for the F-Iine and 1-5814 for the H-line. Similar results were obtained by M. SprockhofE, and for rubidium bromide, 1 5483 for the C-line 1 5528 for the Z)-line and 1 5646 for the F-line. For the caesium bromide, M. SprockhofE obtained T6924 for the C-line 1 6984 for the D-line and 1 7126 for the F-line. The refractive index /u. of soln. of lithium, sodium, and potassium bromides have been determined by G. P. Baxter and for potassium bromide soln. by A. H. Borgesius,27 at 18° for the D-line. The fractional increase in the refractive index (/u.—p0)/w of soln. containing w per cfent. of the salt per litre, is... 

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