Complementary separation, principl

The success of CE is, among others, due to the fact that CE has a complementary separation principle (electromigration) compared with chromatographic techniques (chromatographic partition). As mentioned, the electrically driven mobile phase flow of CE allows for achieving high... 

Hydrophobic interaction chromatography (HIC) was selected because the separation principle is complementary to ion exchange and because a minimum amount of sample conditioning was required. Hydrophobic properties are difficult to predict and it is always recommended to screen different media. 

The principle of 2-D TLC separation is illustrated schematically in Figure 8.4. The multiplicative law for 2-D peak capacity emphasizes the tremendous increase in resolving power which can be achieved in theory, this method has a separating capacity of n, where n is the one-dimensional peak capacity (9). If this peak capacity is to be achieved, the selectivity of the mobile phases used in the two different directions must be complementary. 

GC and GC-MS (see Chapter 2), are ideal for the separation and characterization of individual molecular species. Characterization generally relies on the principle of chemotaxonomy, where the presence of a specific compound or distribution of compounds in the ancient sample is matched with its presence in a contemporary authentic substance. The use of such 6molecular markers is not without its problems, since many compounds are widely distributed in a range of materials, and the composition of ancient samples may have been altered significantly during preparation, use and subsequent burial. Other spectroscopic techniques offer valuable complementary information. For example, infrared (IR) spectroscopy and 13C nuclear magnetic resonance (NMR) spectroscopy have also been applied. 

It is clear from the applications described above that the strength of CE in the field of impurity profiling lies in the various selectivities that can be applied. Not only can one take advantage of electrophoretic phenomena but also of the principle of chromatographic separation and partitioning that is present in techniques such as MEKC and MEEKC. The resolution of substances based on size differences as in CGE is also very useful in the field of biopharmaceuticals. CE can be seen as a complementary technique to other commonly used separation techniques as LC, and in view of its capacity to separate large numbers of compounds, it should certainly always be kept in mind when an analytical problem has to be solved. 

Two general principles that the student should remember are (1) that all substances can under certain circumstances be toxic, and the chemicals in botanicals (herbs and plant extracts) are no different from chemicals in manufactured drugs except for the proportion of impurities and, (2) that all dietary supplements and all therapies promoted as health-enhancing should meet the same standards of efficacy and safety as conventional drugs and medical therapies. That is, there should be no artificial separation between scientific medicine and "alternative" or "complementary" medicine. 

It is for this reason that low amplitude and high amplitude techniques are, in a way, complementary. For the same reason, the use of a sinusoidal perturbation has the unique feature that it enables, in principle, responses of first and higher orders to be obtained separately. If, for example, AE is of the form Em sin cot (co — 2iru is the angular frequency), then the Taylor expansion will contain powers of sin cot, that can be reduced to harmonic terms... 

Figure 5-16. Principle of the polymerase chain reaction (PCR). The polymerase chain reaction relies on primer-dependent replication of a double stranded DNA template. At the beginning of the reaction, the double stranded DNA is denatured and two primers complementary to defined regions on the two strands are hybridised to the separated strands by annealing.

Fig. 13.7 The operating principle of the SERS-based molecular sentinel (MS) nanoprobes, (a) The MS nanoprobe is composed of a Raman-labeled DNA hairpin probe and a silver nanoparticle. In the absence of the complementary target DNA, a strong SERS signal is observed due to the hairpin conformation adopted by the MS nanoprobe (left closed state), (b) In the presence of the complementary target DNA, the hairpin conformation of the MS nanoprobe is disrupted and the SERS signal is quenched due to the physical separation of the Raman label from the surface of the silver...

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