Combination with other chromatographic methods

It is also becoming more common to combine IEC with other chromatographic methods to optimize glycoprotein characterization. Takahashi160 has developed a three-dimensional sugar mapping technique utilizing three different HPLC columns a DEAE column, a hydrophobic octadecylsilica... 

Both small and large analytes can be determined using direct detection in lAC. Additionally it is possible to use this technique either separately or in combination with other chromatographic techniques [1]. If this technique is performed as part of HPLC system the method can be referred as high performance immunoaffinity chromatography. 

DSC is increasingly being applied to the study of epoxy resin cure in combination with other analytical methods such as nuclear magnetic resonance and Fourier transform infra-red spectroscopy, chromatographic methods, and dynamic mechanical or dielectric studies. It is probably as part of such combined investigations that DSC can be used most effectively in basic research, and in quality control and assessment. 

One very important advantage of the SPME technique is that it can be combined with other chromatographic or spectroscopic processes. Thermal desorption of the SPME-concentrated compounds into the carrier gas stream of a gas chromatograph equipped with an FPD or NPD allows rapid screening for nitrogen- or sulfur-containing molecules. If SPME is combined with mass spectrometry, it is possible to identify any analyte (SPME-GC/MS). If sensory evaluation of the separated flavor compounds is necessary, the SPME method can be combined with gas chromatography-olfactometry (SPME-GC/O) (Fig. 13). Last,... 

In conclusion one can say that SEC is a very powerful method for polymer characterization, especially in combination with other composition sensitive or absolute calibration methods. A big advantage is also that the sample amount is fairly small, typically 10 mg. For more complex polymers, such as polyelectrolytes, enthalpic effects often become dominant and also for rather high molecular weight polymers chromatographic methods such as field-flow fraction (FFF) techniques might be more suitable. For fast routine measurements linear columns are often used. 

Some members of class A high-molecular-mass PBPs were found to bind to moenomycin [64,94], E. coli PBP la and lb were purified by using moenomycin-affinity column chromatography in combination with other column chromatographic methods. 

In order to improve the fuel utilization in a Direct Alcohol Fuel Cell (DAFC) it is important to investigate the reaction mechanism and to develop active electrocatalysts able to activate each reaction path. The elncidation of the reaction mechanism, thus, needs to combine pnre electrochemical methods (cyclic voltammetry, rotating disc electrodes, etc.) with other physicochemical methods, such as in situ spectroscopic methods (infrared and UV-VIS" reflectance spectroscopy, or mass spectroscopy such as EQCM, DEMS " ), or radiochemical methods to monitor the adsorbed intermediates and on line chromatographic techniques"" to analyze qnantitatively the reaction products and by-products. 

Mass spectrometers are often used in combination with other instruments. Since a mass spectrometer is an identification instrument, it is often paired with a separation instrument like a chromatograph. Sometimes two mass spectrometers are paired, so that a mild ionization method can be followed by a more vigorous ionization of the individual fragments. 

Thus, for instance, the formation of trimethylsilyl esters, alcohols and phenols or other hydroxyl-containing compounds not only improves chromatographic separations, but also is a method for the analysis of hydroxyl groups. The reagents used in this instance are, however, not very selective as they react with several classes of compounds. For instance, N,0-bis(trimethyl)acetamide also reacts with organic acids, amines, aromatic amides, urea derivatives and some enols [19, 20]. Therefore, this technique should desirably be used in combination with other methods or for converting involatile... 

The above-mentioned approaches take for granted that the spectra of all the reactants are known. This is not at all the case in kinetic analysis, although usually at least the intermediates are unknown. As is demonstrated in Chapter 5, even reactions can be evaluated under these circumstances. But usually the constants obtained from the over-determined system of differential equations are only proportional to the interesting kinetic constants or a combination of them. For this reason absorption spectroscopy is likely to be combined with other methods. An example of combination with fluorescence and with chromatographic principles is given in Chapter 5. 

Every one of these principles of separation can be applied also in thin-layer chromatography, which usually gives better separations in shorter time the method has thus rapidly become iudispensable in lipid chemistry. The efficiency and scope of TLC may be extended still further by combination with other separation techniques. Adsorption TLC and partition chromatographic procedures, i.e., reversed phase partition TLC, paper or gas chromatography, should be used consecutively. Mixtures of compounds which cannot be fractionated by adsorption chromatography can usually be separated by reversed phase partition chromatography and vice versa. 

Before the fatty acid components of lipids can be anaiysed by GC, it is necessary to convert them to iow moiecuiar weight non-poiar derivatives, such as methyi esters, in addition, it may be advisable to mask other poiar functionai groups in a similar manner, or to prepare specific derivatives as an aid to identification. Peak shape and resolution are greatiy improved at the same time, it is only possible to identify fatty acids tentativeiy by GC retention times aione, but GC used in combination with derivatization and chemicai degradative or spectroscopic procedures, especially mass spectrometry, can be an extremely powerful means of characterisation. Of course, such derivatives are aiso of vaiue in isoiating specific fatty acids by other chromatographic methods. Therefore, before any chromatographic procedure is undertaken, it is necessary to consider what derivatives should be prepared and what method should be employed for the purpose. 

Chromatographic methods such as HPLC, GC and their combinations with other methods, such as GC-MS and GC-FTIR, must be utilized for the qualitative and quantitative determination of stabiiizers and other additives. Specimens often have to undergo extensive advance preparation, such as separations and enrichments in the form of extractions and polymer separation by precipitation. 

Separation and detection methods Very refined chromatographic and electrophoretic separation techniques have been developed for metallothioneins. The detection is commonly based on the retention time and UV detection. Other researchers measured the element with e.g. ICP-MS to quantify the compotmd. Combination with electrospray MS-MS leads to the unequivocal identification of the species. 

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