Spectroscopy phase-selective

S. Vaucher, J.-M. Catala-Civera, A. Sarua, 1. Pomeroy and M. Kuball, Phase selectivity of microwave heating evidenced by Raman spectroscopy, J. Appl. Phys., 99, 113505/1-113505/5 (2006). 

Arsenin 11 has been structurally characterized by X-ray crystallography <1997OM4089>. 2,3,6-Triphenylarsenin 12 had been the only prior arsenin so characterized <1973JCD511>, although the structure of the parent arsenin 1 had been determined in the gas phase using electron diffraction <1975JST65> and microwave spectroscopy <1975JSP428>. Selected structural parameters of 11, 12, and 1 are collected in Table 1. 

Lemaire J, Boissel P, Heninger M, Mauclaire GB, G, Mestdagh H, Simon A, Le Caer S, Ortega JM, Glotin F, Maitre P. (2002) Gas phase infrared spectroscopy of selectively prepared ions. Phys Rev Lett 89 273002/1-273002/4. 

Conoscopic studies suggest that this compound in fact exhibits a biaxial nematic phase although these experiments indicated only a small opticd biaxiality. Indeed, more recently, NMR spectroscopy using selectively deute-rated materials has shown that for other materials the assignment of a biaxial nematic phase on the basis of conoscopy alone is not necessarily reliable [118], This is discussed further in Sect, 3,4,... 

See also Capillary Electrophoresis Overview. Chir-optical Analysis. Liquid Chromatography Column Technology Mobile Phase Selection Reversed Phase Instrumentation Amino Acids. Mass Spectrometry Peptides and Proteins. Nuclear Magnetic Resonance Spectroscopy Techniques Nuclear Overhauser Effect. Proteins Traditional Methods of Sequence Determination Foods. 

Impedance measiuements are useful for resistive as well as for capacitive sensors. Analytes can affect the different components of the equivalence circuit in various ways. By impedance spectroscopy, i.e. by phase selective determination of the complex quantities, maximiun sensitivity and selectivity can be achieved. Impedance in this case is not the preferred method in fundamental research its greatest usefulness is in analytical applications. It is aimed at a cahbration curve as hnear as possible. 

Since transport rates change with time due to the presence of salt in the receiving phase, selectivity may also change in time. In order to investigate the time dependency of selectivity, transport of potassium in the presence of sodium has been investigated using different calix[4]crown-5 carriers and valinomycin. The amount of Na and in the receiving phase was measured by atomic absorption spectroscopy after 2 and 24 hours of transport. The results are presented in Table 8. 

A 2D MAS experiment that provides information about orientational order based on spin-1/2 chemical shift anisotropies was introduced by Harbison and other workers [26,47]. Compared to NMR spectroscopy of selectively deuterated liquid crystals, no isotopic labeling is required for this experiment. Spinning side-band spectra of oriented samples show variations in the phases and intensities of the spinning sidebands, which depend on the degree of order present and the position of the rotor at the start of acquisition of the NMR signal. These variations can be translated into a 2D side-band pattern by making the initial rotor position a function of the evolution time ti of a rotor-synchronized 2D NMR experiment. From the side-band intensities of the 2D spectrum, the moments of the orientational distribution function can be extracted. 

Solid state NMR is a relatively recent spectroscopic technique that can be used to uniquely identify and quantitate crystalline phases in bulk materials and at surfaces and interfaces. While NMR resembles X-ray diffraction in this capacity, it has the additional advantage of being element-selective and inherently quantitative. Since the signal observed is a direct reflection of the local environment of the element under smdy, NMR can also provide structural insights on a molecularlevel. Thus, information about coordination numbers, local symmetry, and internuclear bond distances is readily available. This feature is particularly usefrd in the structural analysis of highly disordered, amorphous, and compositionally complex systems, where diffraction techniques and other spectroscopies (IR, Raman, EXAFS) often fail. 

The geometric parameters of the three-membered ring sulfones and sulfoxides have been determined via X-ray diffraction techniques and gas-phase microwave spectroscopy. The accumulated data for some selected thiirane and thiirene oxides and dioxides (16-19) as well as for the corresponding thiirane (20) and the acyclic dimethyl sulfone (for the sake of comparison) are given in Table 3, together with the calculated values. 

The most significant differences (i.e. independence) in the analytical methods are provided in the final chromatographic separation and detection step using GC/ MS and LC-FL. GC and reversed-phase LG provide significantly different separation mechanisms for PAHs and thus provide the independence required in the separation. The use of mass spectrometry (MS) for the GC detection and fluorescence spectroscopy for the LG detection provide further independence in the methods, e.g. MS can not differentiate among PAH isomers whereas fluorescence spectroscopy often can. For the GC/MS analyses the 5% phenyl methylpolysiloxane phase has been a commonly used phase for the separation of PAHs however, several important PAH isomers are not completely resolved on this phase, i.e. chrysene and triphenylene, benzo[b]fluoranthene and benzofjjfluoranthene, and diben-z[o,h]anthracene and dibenz[a,c]anthracene. To achieve separation of these isomers, GC/MS analyses were also performed using two other phases with different selectivity, a 50% phenyl methylpolysiloxane phase and a smectic liquid crystalline phase. 

---