Determination of species

The techniques used in the work have generally been spectroscopic visible-uv for quantitative determinations of species concentrations and infrared-Raman for structural aspects of the polymer. Although the former has often been used in the study of plutonium systems, there has been considerably less usage made of the latter in the actinide hydrolysis mechanisms. 

This example shows that the method discussed can deal with the difficulties frequently met in real situations. One of the products (D) was difficult to measure and another one (F) not accurately analyzed. So the balance could not close and conventional methods of determining stoichiometry via balancing could fail. The standard error in determination of species (C) was in the range of 6-14 % of the measured value in the first period of the experiment . Despite these difficulties, two simple reactions were found with stoichiometry that can adequately represent the reactions. The final representation of the chemical system is not unique but the final stoichiometric coefficients are within 10 % of the original ones. This indicates that the proposed methodology can yield reasonable approximations. 

Figure 3.40 — Sensor for the indirect chemiluminescence determination of species based on electrode generation of OH" ions. (Reproduced from [272] with permission of Elsevier Science Publishers).

The use of selective electrodes for indirect determinations of species to which the sensor responds by a reaction involving the analyte as the primary... 

Determinations by both techniques can be subject to chemical and/or physical interference effects caused by the sample matrix. However, after fractionation of the sample the species are usually in a less complex matrix, a buffer or electrolyte solution. Consequently, matrix interferences effects are minimised. On the other hand, the species may be diluted in the process and this could be detrimental for the determination of species present at very low concentrations. At the present state of the art GFAAS can be used for the determination of analytes at the 1 pgl level. However, at this level contamination in the reagents and equipment limit the number of species that can be detected with confidence. 

In contrast to its MIR counterpart, an important application of NIRS is the routine quantitative determination of species, such as water, proteins, hydrocarbons, and fats, for example, in food or feed products, but also in the petroleum and chemical industries. Figure 13 illustrates a collection of spectra from a pharmaceutical product with varying water content. It shows that a quantitative application can be... 

Direct determination of species. With a combination of techniques (e.g. GC and AAS) several distinct organic species can be isolated and determined, e.g. organo-lead, -mercury and -tin compounds (Chau and Wong, 1983). Also the distinction of several organic and inorganic species of As (Braman et al., 1977 Andreae, 1977) and Sb (Andreae, 1983) have been reported. 

The determination of species concentrations tends to be more challenging than determination of total element contents because... 

Sequential extraction procedures have been applied for the purpose of isolating species of elements from particulate materials, soils and sediments (see Chapters 10 and 11). In sequential extraction procedures, samples are treated with a series of chemicals under rigorously controlled conditions of temperature, time and ratio of reactant to sample. The work of Tessier et al. (1979) resulted in a carefully designed procedure for the determination of species of elements in sediments. It has been used and modified by other investigators. Trace elements in the extracts are usually determined by means of AAS, ICPAES and ICP-MS. An example is the study of sequential extractions for the determination of 20 trace elements in ten certified geological reference materials (Hall et al., 1996). 

Electrochemical methods have been used for determinations of species of elements in natural waters. Of the many electrochemical techniques, only a few have proved to be useful for studies of speciation in complex samples, and to possess the sensitivity required for environmental applications. The greatest concern is the measurement of the toxic fraction of a metal in an aqueous sample. The definition of a toxic fraction of a metal is that fraction of the total dissolved metal concentration that is recognised as toxic by an aquatic organism. Toxicity is measured by means of bioassays. Elowever, a universally applicable bioassay procedure cannot be adopted because the responses of different aquatic species to metal species vary. Nevertheless, bioassays should be used as means of evaluation and validation of speciation methods. A condition is that the test species (of the bioassay) should be very sensitive to the metals being studied so as to simulate a worst case situation (Florence, 1992). 

The inelastic processes - spontaneous Raman scattering (usually simply called Raman scattering), nonlinear Raman processes, and fluorescence - permit determination of species densities as well as temperature, and also allow one, in principle, to determine the temperature for particular species whether or not in thermal equilibrium. In Table II, we categorize these inelastic processes by the type of the information that they yield, and indicate the types of combustion sources that can be probed as well as an estimate of the status of the method. The work that we concentrate upon here is that indicated in these first two categories, viz., temperature and major species densities determined from vibrational Raman scattering data. The other methods - fluorescence and nonlinear processes such as coherent anti-Stokes Raman spectroscopy - are discussed in detail elsewhere (5). 

Wine is a very complex matrix and the accurate, selective determination of species constitutes a challenge for analytical chemists. Furthermore, the speciation analysis of metals bound to biological ligands is a subject of increasing interest since complexation may reduce their toxicity and bioavailability. There is a limited number of studies concerning the speciation analysis of metals or metalloids in wines. Arsenite, arsenate, MMA, and DMA were separated in less than 10 min by means of an anion-exchange column [88], Arsenic species detection was accomplished by the direct coupling of the column effluent to an HG system and AFS was used for detection. LoDs in white wine were 0.16, 0.33, 0.32, and 0.57 ng ml-1 for As(III), DMA, MMA, and As(V), respectively. In real samples... 

The - electrochemical window of polished solid silver amalgam electrode (p-AgSAE) as for an electrode which does not contain liquid mercury is exceptionally broad. This fact allows the application of p-MeSAE for determination of species at rather negative potentials. An important advantage is that the electrodes from solid amalgams of different metals can be prepared in a relatively simple way, and that in their applications specific interactions between these metals and the studied compounds can be utilized. 

Proteins such as cytochrome c are not good target antigens for the determination of species of origin because the structures of these proteins in evolutionarily distant species are very similar. Serum albumin, on the other hand, is a rapidly changing protein (Table I) that is amenable to complete immunochemical analysis with both polyclonal and monoclonal antibodies (14-16). Albumins from thousands of pairs of vertebrate species have been compared immunochemically, and the results have been used to measure evolutionary distances (22). 

Because of these reasons, the determination of the total concentration of a metal in a given matrix is often inadequate as a useful characterization, and speciation has gained considerable ground. Speciation is the process yielding evidence of the atomic or molecular form of an analyte. It can be defined either functionally (e.g., the determination of species that have certain specific functions such as their availability to plants), or operationally (e.g., the determination of the extractable forms of an element). 

The following methods are available for determination of species composition and damage thresholds ... 

Determination of species in rubbers and migrants in food simulants and food products... 

Freeze-dried serum provides no advantage over serum frozen at -30°C in the determination of species such as glucose, urea, nitrogen, sodium, potassium, total protein and... 

Determination of species Rapid identification of a cell line / /... 

The seed morphological characters of species can be used as a taxonomic trait, but should be combined with other traits for the diagnostic determination of species. 

Species extrapolation. The model was developed and validated using the male Sprague-Dawley rat. No other species were tested and data from other species were not used to validate the model. The authors, however, suggest that this model would prove useful in developing better rate constants or other important determinants of species differences (for example, demethylation rates, which differ based on differences in gut flora and tissue enzyme levels). 

---