Sample preparation for XRF-AA-ICP-CHEM.
INSTRUMENTATION
PEAK QUALITY
(a)
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Claisse Fluxes (Borates and Phosphates)
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\ J e t a new perspective on analysis and better results. The CLAISSE FLUXES have exceptional qualities due to their PURITY and COARSE texture.
Claisse Fluxes are Tip-Top. FEATURES • free-flowing crystals • low surface area • high density • fused, not mixed • popular and special compositions CONSEQUENT ADVANTAGES . • no loss from static electricity • no loss by splattering or foaming on heating • very low water absorption • no uncertainty on quantity weighed • no segregation in containers • FREE SAMPLE upon request
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2522, chemin Sainte-Foy Sainte-Foy (Québec) Canada G1V 1T5 Tel: (418)656-6453 Fax:(418)656-1169 Telex: 051-31731
The First and Finest in Fusion.
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205
210 Mass
Figure 4. Resonance ionization mass spectra of (a) Pb and (b) Bi derived from a common sample. The Ionization wavelength for (a) is 450.3 nm and for (b) is 456.6 nm. (Adapted from Reference 11.)
abundance mixtures, there is no isobar ic interference; Bi is monoisotopic (mass 209), and Pb has four isotopes (masses 204,206,207, and 208). Isobaric interferences occur with radioactive isotopes of these elements and their transmutation products. The mass spectrum of a mixture of natural Bi and P b obtained by RIMS is shown in Fig ure 4. The mass spectra of Pb and Bi are obtained at wavelengths of approx imately 450.3 and 465.6 nm, respective ly; these wavelengths correspond to a single-color laser resonance ionization involving, in this case, 2 + 1 optical processes for both elements. By using RIMS at these laser wavelengths, it is possible to ionize either element, cir cumventing the isobaric interferences in radioactive mixtures. Studies of isotopic selectivity have been carried out by several groups (6). One example of such studies uses a C W stabilized ring dye laser to address a small subset of atomic velocities and therefore reduce Doppler broadening effects. This work was pioneered at Pa cific Northwest Laboratory (12). Re cently it was found that similar subDoppler spectral resolution can be at tained in a properly designed experimental arrangement t h a t in
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cludes a diode laser for excitation of the first bound-bound atomic excitation preceding resonant processes leading to ionization (13). Either technique can lead to enhanced isotopic selectivity for amenable atomic species. Another feature that is unique to RIMS is selectivity for initial atomic states. Gaseous atoms as they are gen erated may not all be in the lowest en ergy (ground) state; rather, they can exist in a number of excited states. Within less than 1 μβ, the excited states that are coupled to lower energy states will lose energy by emission. Ultimate ly, in the absence of collision, the metastable states (i.e., those states that are not optically coupled to lower states) remain. It is often a very difficult prob lem to determine the distribution of metastable states, but it can be accom plished with RIMS. Not only the distri bution, but also the lifetime and branching ratios of the individual ini tial states can be measured by laser res onance ionization techniques. The need to obtain this information for the helium 2S metastable state is the rea son for the original development of RIS (1). Although no work seems to have been done in the area, it is also possible to determine the initial states of gas eous ions by a RIMS process that ulti mately generates a divalent ion. There is an adverse side to the pres ence of initial atomic-state distribu tions. Because gaseous atoms exist in various metastable states, the ultimate sensitivity of RIMS is reduced; a given optical excitation route will yield ions only from the atoms in one initial state. This fact needs to be addressed in fu ture studies of the atomization process. Earlier, we pointed out that one of the unique features of RIMS is its ex cellent sensitivity. Where elemental identification or determination is re quired for trace levels of elements in samples, RIMS has been widely ap plied. It has, for example, been applied to very sensitive determinations of Fe in blood serum (14). Several instru ments using pulsed-ion-beam sample ablation to generate a pulsed-atom plume have been applied to trace ele ment analysis. These specialized in struments have been used to determine various metals from aqueous samples (15) and elemental low-level impurities in semiconductor materials (16). In the latter example, these combination in struments do not compete with other types of mass analyses in sensitivity, such as secondary ion mass spectrome try, for this application; however, they do give alternate routes for determina tion. The RIMS technique has been el egantly applied to ultrasensitive deter minations of trace elements of interest
