Chloride lanthanum

In general, the absorption bands of the actinide ions are some ten times more intense than those of the lanthanide ions. Fluorescence, for example, is observed in the trichlorides of uranium, neptunium, americium, and curium, diluted with lanthanum chloride (15). 

Hardness can also be calculated by summation of the individually deterrnined alkaline earths by means of atomic absorption analysis. Basic samples must be acidified, and lanthanum chloride must be added to minimise interferences from phosphate, sulfate, and aluminum. An ion-selective electrode that utilizes ahquid ion exchanger is also available for hardness measurement however, this electrode is susceptible to interferences from other dissolved metal ions. 

The determination of magnesium in potable water is very straightforward very few interferences are encountered when using an acetylene-air flame. The determination of calcium is however more complicated many chemical interferences are encountered in the acetylene-air flame and the use of releasing agents such as strontium chloride, lanthanum chloride, or EDTA is necessary. Using the hotter acetylene-nitrous oxide flame the only significant interference arises from the ionisation of calcium, and under these conditions an ionisation buffer such as potassium chloride is added to the test solutions. 

Preparation of the standard solutions. For procedure (i) it is necessary to incorporate a releasing agent in the standard solutions. Three different releasing agents may be used for calcium, (a) lanthanum chloride, (b) strontium chloride and (c) EDTA of these (a) is the preferred reagent, but (b) or (c) make satisfactory alternatives. 

In contrast, less is known about La-(CNx) compounds. The composition La2(CN2)3 was reported many years ago [43], without any structural information. Solid-state metathesis reactions of lanthanum chloride with Li2(CN2) or Zn(CN2) have recently brought up three series of the lanthanide compounds Ln2(CN2)3 [44], LnCl(CN2) [45], and Ln2Cl(CN2)N [46], Syntheses routes for Ln-(CNx) compounds containing new anions such as [C2N4] are to be developed, as well as for compounds in the La-B-C-N system (Fig. 8.15). 

Bermejo-Barrera et al. [64] studied the use of lanthanum chloride and magnesium nitrate as modifiers for the electrothermal atomic spectrometric determination of p,g/l levels of arsenic in seawater. 

ScF3 and LaF3. Both separate and multilayer scandium and lanthanum fluoride films have been grown from nitrates and lanthanum chloride and sodium and ammonium fluorides. XPS analysis revealed that the films were stoichiometric and that the films contained both hydroxide groups and water.129... 

There are a number of interferences that can occur in atomic absorption and other flame spectroscopic methods. Anything that decreases the number of neutral atoms in the flame will decrease the absorption signal. Chemical interference is the most commonly encountered example of depression of the absorption signal. Here, the element of interest reacts with an anion in solution or with a gas in the flame to produce a stable compound in the flame. For example, calcium, in the presence of phosphate, will form the stable pyrophosphate molecule. Refractory elements will combine with 0 or OH radicals in the flame to produce stable monoxides and hydroxides. Fortunately, most of these chemical interferences can be avoided by adding an appropriate reagent or by using a hotter flame. The phosphate interferences, for example, can be eliminated by adding 1 % strontium chloride or lanthanum chloride to the solution. The strontium or lanthanum preferentially combines with the phosphate to prevent its reaction with the calcium. Or, EDTA can be added to complex the calcium and prevent its combination with the phosphate. 

Several recent determinations of the alkali and alkaline earth metals in serum or urine have been reported. Barrett 29) determined potassium, sodium, and calcium in semm by diluting the samples with lanthanum chloride solution. Suttle and Field 3°) used atomic absorption spectroscopy to determine potassium and magnesium in sheep plasma. 

More recent determinations of serum iron have been reported by Schmidt 57), who simply diluted with lanthanum chloride solution, and by Tavenier and Hellen-doorn58), who deproteinized samples in the latter study, iron in the protein precipitate is analyzed to correct the serum iron level. Uny etal. 59) determined serum iron, using ultrasonic nebulization of the sample to increase the sensitivity. Olson and Hamlin 6°) have determined serum iron and total iron-binding capacity. Proteins are precipitated and iron (III) is released by heating with trichloroacetic acid. 

Figure 6.1 An energy-level diagram for trivalent lanthanide rare earth ions in lanthanum chloride (after Dieke, 1968).

EXAMPLE 6.2 Determine the nonradiative rates from the following energy levels of different ions in lanthanum chloride 5/2 (Er )fPo (Pr +) and 2 5/2 (Yif+). 

Releasing agent - dissolve 2.68 g lanthanum chloride heptahydrate (LaClj.ZH O) in water and make up to 100 ml. 

Also high purity lanthanum may be produced by electrolysis of a molten mixture of anhydrous lanthanum chloride and sodium chloride or potassium chloride at elevated temperatures. 

Lanthanum chloride is used to prepare other lanthanum salts. The anhydrous chloride is employed to produce lanthanum metal. 

Lanthanum chloride reacts with hydrogen sulfide when heated at 1100°C, forming lanthanum sulfide ... 

The addition of hydrofluoric acid to an aqueous solution of lanthanum chloride precipitates out lanthanum fluoride, LaFs ... 

Lanthanum chloride is reduced to lanthanum metal when heated with an alkali or alkaline earth metal at temperatures above 1000°C ... 

Elemental composition La 56.63%, Cl 43.36%. The salt and its hydrate may be characterized by x-ray methods. Water of crystallization may be determined by gravimetry. Lanthanum may be analyzed by flame or furnace AA or by ICP-AES methods (See Lanthanum). Chloride ion in an aqueous solution of the salt may be measured by titration with a standard solution of silver nitrate or mercuric nitrate or by ion chromatography following appropriate dilution. 

The hydroxide is strongly basic. It reacts with acids undergoing neutralization reactions i.e., reaction with HCl or HNO3 yields hydrated salt of lanthanum chloride or nitrate on evaporation and crystalhzation of the solution. It reacts with ammonium salts displacing ammonia ... 

Heating the oxide with an excess of ammonium chloride yields lanthanum chloride ... 

Anions such as sulphate and phosphate form involatile salts with metal ions and reduce the reading of the sample solution. These anions may be removed by the addition of lanthanum chloride which precipitates them out and replaces them with the chloride anion. 

The element M will be more readily liberated if compound R-X is more stable. Thus, when calcium is to be measured in a matrix rich in phosphate ions or in refractory combinations containing aluminium, then sodium or lanthanum chloride is added. The desired effect is to liberate calcium and to increase the volatility of the matrix in order to ensure more efficient elimination during the decomposition step. 

---