HPLC UTILIZATION

Before considering these in detail, it is necessary to revisit the inherent incompatibilities between mass spectrometry and liqnid chromatography. These are, as discussed previously, that HPLC utilizes a liquid mobile phase, often containing significant amounts of water, flowing typically at 1 mlmin while the mass spectrometer must be maintained under conditions of high vacuum, i.e. around 10- torr (1.333 22 x IQ- Pa). 

The main one is the incompatibility of HPLC, utilizing flow rates of ml min of a liquid, and the mass spectrometer, which operates under conditions of high vacuum. Even if this can be overcome, attention must then be focussed on the ionization of the analyte, bearing in mind the limitations of El and Cl discussed earlier in Chapter 3, and the generation of analytically useful mass spectra. 

Phase separation (precipitation) of a polymer strongly depends on all its molecular characteristics. On the one hand, this allows very efficient separations in polymer HPLC utilizing phase separation and re-dissolution processes [20]. On the other hand, due to complexity of phase separation phenomena, the resulting retention volumes of complex polymers may simultaneously depend on several molecular characteristics of separated macromolecules. This may complicate interpretation of the separation results. Both precipitation and redissolution of most polymers is a slow process. It may be affected by the presence of otherwise inactive surface of the column packing. Therefore, the applicability and quantitative control of the phase separation phenomena may be limited to some specific systems of polymer HPLC. 

Because the retention times of the different TGs within a PN differ, it is important to collect the whole peak at fractionation. One total fractionation, with an elution time of ca. 1.5 h, will provide enough material for the subsequent separation procedure based on argentation-HPLC (utilizing silver ions in the mobile phase), in order to separate geometrical isomers. 

Chemical modification of the inner wall of fused-silica capillaries and the surfaces of porous silica supports for HPLC utilize the same reactions. The most common method is based on organosilanization. Within this general reaction scheme, there are two possible... 

Whereas the other separation methods have been demonstrated to also provide the requisite performance for release and stability testing for select drug substances and drug products, more typically the techniques are applied as supportive methods for HPLC during early-phase development and in niche areas during late-phase development. Because each separation method provides a different mechanism of separation to HPLC, utilization in early-phase development can be used to confirm specificity of HPLC methods. In later phases, both SFC and CE have shown applicability to chiral separations, and GC remains as the unique technique for the determination of residual solvents. 

The specific fluidic system involved, while not the main topic of this entry, is closely linked to the detection system and warrants a brief explanation. Separation techniques such as CE and HPLC utilize channels or columns that pass a fluidic medium carrying the analytes of interest. Bulk flow is actuated using either gravity or pressure, in the case of LC, or electroosmotic forces, in the case of CE. Separation of analytes occurs due to physical or chemical interactions with what is incorporated into the column (a packing material that completely fills the column or is... 

Introduction. Ag-HPLC, utilizing columns packed with 5-10 pm Nucleosil SA (TM) (Macherey-Nagel, Diiren, Germany) (phenylsulfonic acid groups bonded to a silica substrate), or a similar substrate in which the sulfonic acid protons have been... 

Anastos N, Lewis SW, Barnett NW, Sims DN (2006) The determination of psilocin and psilocybin in hallucinogenic mushrooms by HPLC utilizing a dual reagent acidic potassium permanganate and tris (2,2-bipyridyl) ruthenium (11) chemiluminescence detection system. J Forensic Sci 51 45-51... 

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