Transport interference technique

Yet, another feature that becomes available with the fast sequential mode of operation in HR-CS AAS is the use of the reference element technique, that is, the use of an internal standard. This technique has rarely been described in LS AAS [3] for a number of obvious reasons. Firstly, the technique requires a dual-or multi-channel spectrometer, and there have been only very few spectrometers of this type available commercially over the past decades. Secondly, the reference element technique is ideally suited to correct for nonspecific interferences, such as transport interferences, but it is notoriously difficult to find an appropriate reference element for element-specific interferences. Thirdly, the most successful multi-channel LS AAS equipment, the Perkin-Elmer Model SIMAA 6000, which has been available for a number of years, was designed for ET AAS only, a technique that does not typically exhibit nonspecific interferences. The number of publications using this technique is therefore very limited. 

The choice of the appropriate mineral acid and oxidant depends on the final analytical technique to be used. For instance, HC1 is not recommended for furnace analysis as it can cause Cl interferences, while H2S04 is not desirable with ICP-AES or ICP-MS because of transport interferences derived from its viscosity. With ICP-MS HNO3 and H202 are preferred since the effect of polyatomic interferences is minimal as compared with HC1, HC104 and H2S04, which introduce polyatomic ions such as C10+ and SO+ [28-32]. In any case, in order to minimize corrosion of the metal sampler and skimmer cones with ICP-MS, final sample solutions should not contain high acid concentrations (e.g., above 10 percent for HNO3). 

Among the nonspectral interferences transport interferences in the nebulizer are relatively common in the analysis of body fluids. This is certainly no problem when 10- or 20-fold diluted serum is used for the determination of the electrolytes. If, however, undiluted or only slightly diluted body fluids are aspirated directly, the viscosity of these liquids can impair aspiration rate and nebulization efficiency relative to the reference solutions used. If the sample solution cannot be diluted sufficiently to avoid this interference, a frequently used alternative is matrix-matched standards, i.e., reference solutions with a viscosity close to that of the samples. Another alternative is to use the method of additions, which can perfectly correct for this interference. This calibration technique, however, is labor-intensive and time consuming, and is restricted to the linear part of the calibration curve. Viscosity of the sample solutions is much less of a problem when FI techniques are used for sample introduction. This is because samples are not aspirated but pumped to the nebulizer, because much smaller sample volumes are used, and because the sample is always in a carrier solution which supports nebulization and removes all potential residues in the nebulizer-bumer system. 

A term that is nearly synonymous with complex numbers or functions is their phase. The rising preoccupation with the wave function phase in the last few decades is beyond doubt, to the extent that the importance of phases has of late become comparable to that of the moduli. (We use Dirac s terminology [7], which writes a wave function by a set of coefficients, the amplitudes, each expressible in terms of its absolute value, its modulus, and its phase. ) There is a related growth of literature on interference effects, associated with Aharonov-Bohm and Berry phases [8-14]. In parallel, one has witnessed in recent years a trend to construct selectively and to manipulate wave functions. The necessary techniques to achieve these are also anchored in the phases of the wave function components. This trend is manifest in such diverse areas as coherent or squeezed states [15,16], electron transport in mesoscopic systems [17], sculpting of Rydberg-atom wavepackets [18,19], repeated and nondemolition quantum measurements [20], wavepacket collapse [21], and quantum computations [22,23]. Experimentally, the determination of phases frequently utilizes measurement of Ramsey fringes [24] or similar methods [25],... 

Probably the most accessible techniques employed for Li+ analyses are AAS and FES [26]. Although both of these methods are destructive to the sample and are subject to significant interference effects, the methods have been developed and used successfully for many years. Li+ levels in solution, in body fluids, and in solubilized tissues have been determined, making a significant contribution to the understanding of Li+ distribution in the body, and of the membrane transport of Li+ in various systems. 

A typical extraction manifold is shown in Figure 13.2. The sample is introduced by aspiration or injection into an aqueous carrier that is segmented with an organic solvent and is then transported into a mixing coil where extraction takes place. Phase separation occurs in a membrane phase separator where the organic phase permeates through the Teflon membrane. A portion of one of the phases is led through a flow cell and an on-line detector is used to monitor the analyte content. The back-extraction mode in which the analyte is returned to a suitable aqueous phase is also sometimes used. The fundamentals of liquid liquid extraction for FIA [169,172] and applications of the technique [174 179] have been discussed. Preconcentration factors achieved in FIA (usually 2-5) are considerably smaller than in batch extraction, so FI extraction is used more commonly for the removal of matrix interferences. 

Interfacial rheological parameters can be determined in various ways. Preferably experiments should be carried out either in pure dilation or in pure shear but in practice it is difficult to avoid interference between these two. All techniques have in common that the area is in some fashion deformed (l.e. sheared, compressed or dilated) and the rheological response measured. Interpretation requires accounting for momentum transport which can take place in the monolayer itself or by transfer to (or from) the adjacent bulk phases. 

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