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【多选题】
Write down basic principles and applications of gas chromatography, high-performance liquid chromatography and capillary electrophoresis.
A.
CE: separations of large organic species on the basis of their rate of migration through a medium under the effect of an electrical gradient, which is determined by the mass and charge of the species, the permeability of the supporting medium, and of course the magnitude of the electrical gradient. Hence species can often be separated on the basis of differences with regard to these characteristics. Better resolution than for similar HPLC separations can thus be obtained. Detection of the eluted components is typically achieved using detectors based on molecular spectrometry.
B.
Gas chromatography: To provide the higher resolutions required by modern analyses, the use of long, small diameter capillary columns is the norm. Contemporary GC analysis of trace organic materials uses open tubular capillary columns where a liquid phase has been bound to the internal wall.
C.
HPLC is almost exclusively performed in the reverse phase mode (RP-HPLC), using stationary phases of silica gel derivatised with silylated aliphatic hydrocarbons such as octasilyl (C-8) and octadecylsilyl (ODS) moieties. These are used in conjunction with mobile phases that are predominantly aqueous. HPLC is of most utility where the organic analytes have a large molecular mass, and hence have low volatility, and where the molecule is polar or contains many polar substituents.
D.
Atomic absorption spectrometry (flame or electrothermal) (AAS, ET-AAS), atomic fluorescence spectrometry (AFS), inductively coupled plasma optical (or atomic) emission spectrometry (ICP-OES or ICP-AES), neutron activation analysis (NAA), X-ray fluorescence (XRF), proton-induced X-ray emission (PIXE), spark source or isotope dilution mass spectrometry (SSMS, IDMS), electrochemical (anodic stripping voltammetry and polarography) or inductively coupled plasma-mass spectrometry (ICP-MS).
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