Transport interference

Defects of mitochondrial transport interfere with the movement of molecules across the inner mitochondrial membrane, which is tightly regulated by specific translocation systems. The carnitine cycle is shown in Figure 42-2 and is responsible for the translocation of acyl-CoA thioesters from the cytosol into the mitochondrial matrix. The carnitine cycle involves four elements the plasma membrane carnitine transporter system, CPT I, the carnitine-acyl carnitine translocase system in the inner mitochondrial membrane and CPT II. Genetic defects have been described for each of these four steps, as discussed previously [4,8,9]. 

Physical (transport) interferences. This source of interference is particularly important in all nebulisation-based methods because the liquid sample must be aspirated and transported reproducibly. Changes in the solvent, viscosity, density and surface tension of the aspirated solutions will affect the final efficiency of the nebulisation and transport processes and will modify the final density of analyte atoms in the atomiser. 

There may well, on occasions, be people reading this book who wish to make sure that their data is reliable, but who cannot afford either the time delay or the cash outlay needed to acquire a selection of appropriate certified reference materials. Fortunately, there are other useful approaches worthy of consideration which allow detection of spectral, chemical, or transport interferences in analytical flame spectrometry. 

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). 

Nonspectral interferences affect the analyte signal, i.e., the number of analyte atoms in the absorption volume (absolute or per unit time) directly. They are best classified according to the place or stage at which the particular interference occurs, i.e., transport, volatilization, vapor phase, or spatial distribution interferences. Because the mechanisms of nonspectral interferences depend very much on the particular atomizer used, they will be discussed in detail in the following Sects. 2.2, 3.2, and 4.2. Nonspecific interferences, such as transport interferences caused in the... 

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. 

Another group of elements which is frequently determined by FAAS is copper, iron, and zinc in tissues and body fluids, and total iron-binding capacity. Concentrations of these elements are significantly lower compared to the electrolytes, so that samples cannot be diluted very much. This means that the viscosity of the measurement solutions must be carefully controlled in order to avoid transport interferences. A recent review article by Taylor [7] gives a concise overview over clinical applications of FAAS. 

One of the advantages of ETAAS is that it is fiee from transport interferences because usually no nebulizers are used for sample introduction. A measured volume of sample is deposited on the platform in the atomizer by an autosampler, so that sample viscosity and other physical parameters do not play a significant role. The major sources of errors in ETAAS are loss of the analyte element by volatilization in the pyrolysis stage prior to atomization and the formation of stable compounds with concomitants in the gas phase. 

The most important compound is 2-mercapto-pyridine-A -oxide = Pyrithione. According to Albert (1968) its mechanism of antimicrobial activity is based on chelation complex formation. But there are findings (Cooney Felix, 1972 Chandler Segel, 1978) which demonstrate that other modes of action are involved, too, for example, influence on ATP levels, nutrient transport, interference with protein synthesis. 

The acid concentration in the final solution being presented to the instrument should ideally be 2-3% maximum because of the sample transport interferences associated with high concentrations of mineral acids. 

During method development, special attention must be given to correct for matrix and spectral interferences. Matrix suppression and sample transport interferences are compensated very well by the selection of suitable internal standards, which are matched to the ionization properties of the analyte elements. This is a routine and... 

During method development, special attention must be given to correct for matrix and spectral interferences. Matrix suppression and sample transport interferences are... 

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