Identification of Atomic Species

Applications of ultraviolet spectroscopy to the identification of atomic species and simple polyatomic molecules are well defined (Refs 1,... 

The application area for thermochromic pigments is vast indeed. In the context of indicators they may be used for visual density identification of atomic species caused... 

In conclusion the experimental support given by the use of molecular probes to the molecular approach to chemisorption considered as a localized interaction of chemisorbed molecules with metal atoms on the surface of metals or metal oxides [2, 5] was at the origin of the development of a more precise experimental identification of surface species involved in some aspects of heterogeneous catalysis. 

Several spectroscopic techniques, namely, Ultraviolet-Visible Spectroscopy (UV-Vis), Infrared (IR), Nuclear Magnetic Resonance (NMR), etc., have been used for understanding the mechanism of solvent-extraction processes and identification of extracted species. Berthon et al. reviewed the use of NMR techniques in solvent-extraction studies for monoamides, malonamides, picolinamides, and TBP (116, 117). NMR spectroscopy was used as a tool to identify the structural parameters that control selectivity and efficiency of extraction of metal ions. 13C NMR relaxation-time data were used to determine the distances between the carbon atoms of the monoamide ligands and the actinides centers. The II, 2H, and 13C NMR spectra analysis of the solvent organic phases indicated malonamide dimer formation at low concentrations. However, at higher ligand concentrations, micelle formation was observed. NMR studies were also used to understand nitric acid extraction mechanisms. Before obtaining conformational information from 13C relaxation times, the stoichiometries of the... 

The identifications of atomic and molecular species is undertaken with a variety of mass spectroscopies. Time-of-flight (TOF) mass spectroscopy is of value for very short lived or highly peaked emissions. More sustained emissions are more readily studied with a quadrupole mass spectrometer (QMS), which can be tuned to a single mass peak. The time evolution (on a microsecond time scale) of a particular mass emission can be determined from the observed signals. Under the appropriate conditions, both these tools can be applied to studies of neutral emission (with ionizer) and positive or negative ion emission (without ionizer). 

The digital code for identification of these species may be interpreted as follows the units digit is the number of fluorine atoms in the molecule, the tens digit is the number of hydrogen atoms plus one, the hundreds digit is the number of carbon atoms minus one (and is dropped if equal to zero) the residue of atoms required to saturate the carbons is assumed to be chlorine. 

A number of recent investigations have shown that mass spectrometry (MS) is a rapid and effective method for the identification of triacylglycerol species of milk fat that are compositionally different (Myher et al., 1988, 1993 Laakso and Kallio, 1993 Spanos et al., 1995 Laakso and Manninen, 1997 Mottram and Evershed, 2001 Kalo et al., 2004). In fact, a range of mass spectral techniques, such as electron ionization, fast atom bombardment, chemical ionization, atmospheric pressure chemical ionization and electrospray MS, have been used to study triacylglycerols. The later three are soft ionizing techniques, which retain substantial amounts of the molecular ion, rather than fragmenting the molecule into a number of parts. These methods have allowed the determination of... 

Another class of techniques monitors surface vibration frequencies. High-resolution electron energy loss spectroscopy (HREELS) measures the inelastic scattering of low energy ( 5eV) electrons from surfaces. It is sensitive to the vibrational excitation of adsorbed atoms and molecules as well as surface phonons. This is particularly useful for chemisorption systems, allowing the identification of surface species. Application of normal mode analysis and selection rules can determine the point symmetry of the adsorption sites./24/ Infrarred reflectance-adsorption spectroscopy (IRRAS) is also used to study surface systems, although it is not intrinsically surface sensitive. IRRAS is less sensitive than HREELS but has much higher resolution. 

The simultaneous measurement of the impedance and mass/potential transfer function leads to new information on the kinetics of the processes involved. It may lead to chemical identification of the species involved in the intermediate reaction steps by allowing the atomic masses of the adsorbed intermediates of the multistep reaction mechanisms to be estimated. 

The detection systems used with HPLC can be broadly divided into three approaches photometry, plasma techniques (ICPAES, ICPMS), and cold vapour atomic absorption and fluorescence spectroscopy (CV-AAS, CV-AFS). The method with the lowest limits of detection (LOD) with sample introduction via a direct injection nebulizer used ICP-MS. An HPLC system coupled to atmospheric pressirre chemical ionization MS was used to identify methyl mercury spiked into a fish tissue CRM (DORM-1, NRCC). This type of system has a significant advantage over elemental detection methods because identification of the species present is based on their structure, rather than matching the analyte s retention time to that of a standard. 

The scope and limitations, illustrated by some applications, of atomic and X-ray fluorescence spectroscopy, ion selective electrodes, and other less common methods for impurity analysis will be discussed. The techniques of infrared, Raman, X-ray photoelectron, and sputter induced photon spectroscopy, used for identification of silicate species will be briefly reviewed. 

One of the most powerful techniques used in Upid analysis today is HPLC coupled with mass spectrometry (HPLC/MS). Several mass spectrometric ionization techniques, such as fast atom bombardment (FAB) [23], electrospray ionization (ESI) [29,30], ionspray ionization (ISI) [31], and atmospheric pressure chemical ionization (APCI) [22,30,32] have been used. By using HPLC/MS, one can get information on the molecular structure of the intact lipids, which helps differentiate molecular species within different lipid classes. By using tandem mass spectrometry (MS/MS), identification of molecular species of different sphingolipids can be achieved in an easier and more sensitive way. There are many other advantages of using MS, such as small sample size, minimal sample preparation, and lack of need for derivatization, speeds, and sensitivity. In the literature, sphingolipids of both animal and plant origin were analyzed by MS. 

APS Appearance Potential Spectroscopy Surface (==20 atomic layers) Electrons (energy scan) 50-2000 eV X-rays to pinpoint electron energy threshold Identification of surface species 21, se< also I... 

Many minerals of known structure have been studied by solid state Si NMR [13] and have thus provided a partial basis for identification of silicate species in solution. After pioneering Si NMR work on silicate solutions at low fields [14] had shown that the Si atoms with different connectivities could be easily identified, rapid progress followed and the introduction of sophisticated NMR techniques revealed more detailed information on the nature of silicate solutions. Figure 2 illustrates the power of high-resolution Si NMR very sharp lines allow in principle the distinction of many species. The achievements of this technique or the combination of NMR spectroscopy with chemical trapping have been impressive and include the following ... 

Improvements have been made recently for the preconcentration of gaseous methylmercury in air by preconcentration in mist chambers and subsequent determination by aqueous-phase ethylation, precollection on carbotrap columns, separation by GC, and detection by cold vapor atomic fluorescence spectrometry (CV-AFS). In order to understand the behavior and fate of mercury compounds in the atmosphere and their role in environmental mercury cycling, there is an urgent need for further development of analytical methods to afford identification of mercury species in the atmosphere by compound-specific analytical methods (as opposed to operationally defined protocols). 

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