Capillary electrophoresis transformation techniques

Several additional instrumental techniques have also been developed for bacterial characterization. Capillary electrophoresis of bacteria, which requires little sample preparation,42 is possible because most bacteria act as colloidal particles in suspension and can be separated by their electrical charge. Capillary electrophoresis provides information that may be useful for identification. Flow cytometry also can be used to identify and separate individual cells in a mixture.11,42 Infrared spectroscopy has been used to characterize bacteria caught on transparent filters.113 Fourier-transform infrared (FTIR) spectroscopy, with linear discriminant analysis and artificial neural networks, has been adapted for identifying foodbome bacteria25,113 and pathogenic bacteria in the blood.5... 

Capillary electrophoresis (CE) either coupled to MS or to laser-induced fluorescence (LIF) is less often used in metabolomics approaches. This method is faster than the others and needs a smaller sample size, thereby making it especially interesting for single cell analysis [215] The most sensitive mass spectrometers are the Orbitrap and Fourier transform ion cyclotron resonance (FT-ICR) MS [213]. These machines determine the mass-to-charge ratio of a metabolite so accurate that its empirical formula can be predicted, making them the techniques of choice for the identification of unknown peaks. 

Numerous analyses in the quality control of most kinds of samples occurring in the flavour industry are done by different chromatographic procedures, for example gas chromatography (GC), high-pressure liquid chromatography (fiPLC) and capillary electrophoresis (CE). Besides the different IR methods mentioned already, further spectroscopic techniques are used, for example nuclear magnetic resonance, ultraviolet spectroscopy, mass spectroscopy (MS) and atomic absorption spectroscopy. In addition, also in quality control modern coupled techniques like GC-MS, GC-Fourier transform IR spectroscopy, HPLC-MS and CE-MS are gaining more and more importance. 

Transformation techniques, including CC, HT, and FT, have been successfully combined with CE and ME techniques. Significant improvement in the S/N ratio was achieved for both capillary and microchip electrophoresis when CC and FIT were employed. Fundamental studies of FT-ME and SCOFT have shown promising results, as demonstrated by enhancement in analyte sensitivity. These fundamental studies verified that these techniques work well theoretically and experimentally. However, how these techniques can be used in practical chemical analyses remains unclear. Therefore, further investigation should be aimed at discovery of important applications of these techniques, especially of FT and SCOFT. 

As described in more detail in Section 13.3.2, the main analytical techniques that are employed for metabonomic studies are based on nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). The latter technique requires a preseparation of the metabolic components using either gas chromatography (GC) after chemical derivatization or liquid chromatography (LC), with the newer method of ultra-high-pressure LC (UPLC) being used increasingly. The use of capillary electrophoresis (CE) coupled to MS has also shown promise. Other more specialized techniques such as Fourier transform infrared spectroscopy and arrayed electrochemical detection have been used in some cases. 

One of the main, but not sole, purposes of derivatization is the transformation of non-volatile compounds into volatile derivatives. Each chromatographic method [GC, GC/ mass spectrometry (MS), high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), etc.] being supplemented by derivatization of analytes permits us to solve some specific problems. The principal among them are summarized briefly in Table 1 more detailed comments follow. Some of the derivatization methods mentioned can also be used in mass spectrometry, which includes no preliminary chromatographic separation of analytes, but there are special derivatization techniques... 

Capillary electrophoresis (CE) is electrophoresis performed in a capillary tube, in practice almost always made of fused sihca. Of the techniques available for separation of both large and small molecules in solution, CE has the highest separation efficiency. The transformation of conventional electrophoresis to modem CE was made possible by the production of inexpensive narrow-bore capillaries for gas chromatography (GC), as discussed in Section 4.4.3. The unrivalled resolution and separation... 

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