Lanthanum chloride matrix

U(III) in an alkaline earth fluoride matrix was one of the earlier laser materials 49h). As might be expected with crystalline substances, the splitting of the various J levels can be completely resolved, especially at low temperatures. Thus the polarized absorption spectrum of in a lanthanum chloride matrix (Csh environment) has been measured from 5600 to 25,000 cm and analyzed in detail. The ground state yields 5 sublevels in this symmetry, the state yields 6 sublevels, and 20 lines result from the combination of these two levels (50, 51). 

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. 

The absorption spectrum of Bk(III) in a lanthanum chloride host matrix at 77 K was first obtained in 1964 (102). A prediction of the energy level structure of Bk(III) was made by others the same year (103). Extensive, low-temperature spectroscopic studies of BkCl3 showed the absence of transitions to excited J = 0 and J = 1 states (104, 105). This provided good evidence for a fi = 0 ground level for Bk(III), consistent with that of Tb(III)-LaCl3 (106). Experimental and theoretical studies of the crystal field parameters of Bk(III) in a LaCl3 host lattice have also been reported (107). 

In water and beverages strontium can be measured directly, but food and biological materials require a pretreatment with hydrochloric acid (3 M) and lanthanum chloride [91]. In urine strontium can be determined after dry-ashing and addition of lanthanum [91] or directly after 1 2 dilution with an acidic lanthanum chloride solution [92], The determination of strontium in bone requires special attention because the bone matrix contains high amounts of calcium and phosphate, which can easily interfere with the determination of strontium. Razmilic described a method to isolate strontium from the calcium phosphate matrix by ion exchange chromatography. The pretreated samples then can be analysed by both emission and absorption spectrophotometry measurements without chemical, ionization, or bulk interferences [93,94]. 

Add 2 ml potassium chloride solution and 5 ml lanthanum nitrate solution to reduce matrix disturbances and improve sensitivity. 

Clearly some form of sample pretreatment is required for soils and sediments. Total levels may be obtained following sodium carbonate-boric acid fusion and the dissolution in hydrochloric acid employing lanthanum as a buffer and releasing agent. If the determination of silicon is not required, it may be volatilized as silicon tetrafluoride using hydrofluoric acid, although some calcium may also be lost as calcium fluoride. For many samples, however, it may be more appropriate to determine the exchangeable cation content of the sample. Here, the sample may be shaken with an extractant solution, for example, 1 mol 1 ammonium chloride, ammonium acetate, or disodium EDTA, prior to filtration and analysis. Where final solutions contain more than - 0.5% of dissolved material, the standards should also contain the major constituents, even where no chemical interference is expected, in order to match the viscosity and surface tension and avoid matrix effects. 

A crystal or pressed pellets of an insoluble salt can act as ion sensitive elements operating in much the same way as the salt dispersed in an inert matrix. The crystal is precision ground into a disc shape and fixed onto an electrode body. The manufacturing process is closety controlled to avoid the crystal developing an internal crack or leak. The crystal should also not have high resistance. Examples can be cited of the lanthanum fluoride electrode (measure fluoride) and silver chloride electrode (measures chloride). 

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