Orthogonal separation techniques examples

Table 2.4. Common Examples of Orthogonal Separation Techniques...

CE has been touted as a replacement for HPLC in the pharmaceutical industry. This was a shame, since the techniques are so different. For many measurements, it is an orthogonal technique to HPLC. Whereas HPLC separates based on interaction with the stationary phase, CE separates based on the ratio of charge to mass. There are numerous examples of where CE exceeds the resolving power of HPLC (e.g., ion analysis, chiral analysis, DNA quantification, separation, large molecule analysis, etc.). 

It should be noted that since the mathematical description of the packed bed reactor consists of three dimensions, one does not need to select a single technique suitable for the entire solution but can choose the best technique for reduction of the model in each of the separate dimensions. Thus, for example, orthogonal collocation could be used in the radial dimension where the... 

The rapid separations offered by capillary electrophoresis have made it amenable as a detector in hyphenated techniques. For LC-CE, the total analysis time is usually governed by the LC separation, which generally takes minutes. However, capillary electrophoresis detection adds more peak capacity because of a second and orthogonal dimension for separation, and shorter separation conditions for LC can often be tolerated. For example, a 2.5 min reversed-phase liquid chromatography gradient was used in conjunction with 2.5 s CE separations for the detection of a tryptic digest of cytochrome c. ... 

While not yet active in clinical analysis, two techniques appear to be of great interest two-dimensional (2D) maps and capillary zone electrophoresis (CZE). In 2D maps, denatured polypeptide chains are separated in two dimensions, first by surface charge (lEF) and then orthogonally by size (SDS electrophoresis). In normal human sera, for example, 600 spots are separated and detected by silver staining. 

For example, if each separation mode generates peak capacities of 1100 in the first dimension and 30 in the second, the theoretical peak capacity of the 2D experiment will be 33 000, a huge gain in separation space, which would theoretically compare to the separation power of a 12000 m column in the normal single-dimension analysis. To achieve this gain, however, the two techniques should be totally orthogonal, that is, based upon completely different separation mechanisms. 

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