Phase identification light scattering

Fig. 42 Reversed-phase HPLC profiles of natural (top) and rearranged (bottom) butterfat triacylglycerols as obtained with the light-scattering detector. HPLC conditions Hewlett-Packard Model 1050 liquid chromatograph equipped with a Supelcosil LC-18 column (25 cm X 0.46-cm ID) coupled to a Varex ELSD II light-scattering detector. Solvent linear gradient of 10-90% propanol in acetonitrile at 25°C over a period of 90 min (1 ml/min) recording stopped at 70 min. Peak identification by carbon and double-bond numbers of triacylglycerols.

Ruiz-Sala et al. (129) described a reversed-phase HPLC method with a light-scattering detector for the analysis of TGs in milk fat. The identification of TGs was carried out by a combination of HPLC and gas-liquid chromatography (GLC), and was based on the equivalent carbon numbers and retention times of different standard TGs. Finally, quantitation of peak areas from HPLC chromatograms was carried out after applying a deconvolution program to the parts of chromatograms with poor resolution. 

Dynamic light scattering (DLS) (model B1-9000AT, Brookhaven Instrnments Corp., Holtsville, NY) was nsed to estimate the particle size and particle size distribution of the resulting BT powders. The samples were dilated with deionized water and ultrasonicated for 15 min jnst before the size analysis. Room temperature XRD (Scintag PAD V using CnKa with X = 0.15406 nm) was nsed for crystalline phase identification and determination of the crystallite size of the powder. The crystallite size of BaTiOj powders was calcnlated by the Scherrer eqnation ... 

Detection and identification of related substances caimot be performed by LC-MS alone. In practice, additional experiments are required using various LC gradients and/or orthogonal phase systems, alternative detection techniques like evaporative light scattering detection or optical rotation detection, and other spectroscopic techniques, like UV-DAD and NMR. Obviously, this discussion focusses primarily on the role of LC-MS in the impurity profiling and identification. Developments in LC-MS and especially mass analysers are important in strengthening the power of LC-MS in stmcture elucidation. 

In LC, a means of detection is employed for identification and quantification. While detection is covered elsewhere in this volume, mobile phase selection can play an important role in the detectability of the compounds of interest, and vice versa. A solvents lowest usable (cutoff) wavelength is important for UV detectors, solvent refractive index (RI) effects the sensitivity of RI detection, and solvent volatility is an important consideration for evaporative light scattering and mass spectrophotometric based detectors. Table 4 lists some common LC mobile phase spectral data. 

The interest in the phase behaviour of block copolymer melts stems from microphase separation of polymers that leads to nanoscale ordered morphologies. This subject has been reviewed extensively [1 ]. The identification of the structure of bicontinuous phases has only recently been confirmed, and this together with major advances in the theoretical understanding of block copolymers, means that the most up-to-date reviews should be consulted [1,3]. The dynamics of block copolymer melts, in particular rheological behaviour and studies of chain diffusion via light scattering and NMR techniques have also been the focus of several reviews [1,5,6]. 

Rocha JM, Kalo PJ, Ollilainen V, Malcata XF. Separation and identification of neutral cereal lipids by normal phase high-performance liquid chromatography, using evaporative light-scattering and electrospray mass spectrometry for detection. J Chromatogr A 2010 1217 3013-25. 

The major uses of XRD are identification of crystalline phases, determination of strain, crystalline orientation and size, epitaxial relationship, and the accurate determination of atomic positions (better then in electron diffraction). Because of the strong Z dependence of X-ray scattering, light elements are difficult to deal with, particularly in the presence of heavy elements. 

Identification of systems containing a pyrochlore-type phase is often extremely difficult because of the similarity of this structure to that of fluorite. Thus the cation sub-lattices of these two structures are identical except for the order present in the pyrochlores, and unless there is a substantial difference in the scattering factors of the two cation types in the pyrochlore there will be little indication of this order in the diffraction pattern. Similarly, the only ways in which the pyrochlore anion array differs from that of fluorite are that one eighth of the anion sites of the latter are vacant and six sevenths of the remaining anions are shifted from their ideal fluorite sites. In most relevant systems any contribution from the anion sub-lattice would be small and not greatly different from that of a fluorite anion uray. Pyrochlore-type compounds of oxides of second transition-series metals and those of light rare earth elements, or of the oxides of third transition-series metals and those of heavier rare earth elements, are relatively difficult to distinguish from fluorite. 

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