Có 20+ tài liệu thuộc chủ đề "HPLC Theory"
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Rapid development of MS in recent decades has further expanded its role in the structural characterization of small molecules in the drug discovery process [1].. In combination with chromatographic separation techniques, principally in the form of high-performance liquid chromatography (HPLC. In addition, control of internal energy deposited on ions during ionization should be achievable in the ionization source to control...
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The characteristic isotopic patterns resulting from combi- nations of the isotope peaks can be used to ascertain elemental composition of the corresponding ion.. In the case of Verapamil (Scheme 1), the molecular weight of the com- pound is 420 Da, indicating an even number of nitrogen atoms in the molecule.. The change of chromatographic retention time due to the use...
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The aim of analysis of each HPLC method may vary for each developmental area in the drug development process and specific examples are given in Section 8.2.. These include properties of the analyte, detector, mobile phase, stationary phase, and gradient considerations.. The final part of the chapter provides a refresher on “pK a from an analy- tical chemist’s perspective,” the...
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Also the spectral homogeneity of the peak of interest must be taken into consideration. If the peak is not spectrally homogenous, the overlay of the spectra will show. This does not absolutely ascertain that the peak is homogeneous since isomers of the same compound will have the same [M + H] and is indistin- guishable from the parent compound. and...
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If the retention of the early eluting components are consistent (less than 1% variation in reten- tion time) in all three methods, then the lowest equilibration time could be used. Optimization of the optimal equilibration time is required for reproducible methods.. The dwell volume should be determined for all the systems in the laboratory and based on these determinations, this...
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Extreme changes in selectivity and reversal of elution order of phenolic isomeric compounds were obtained after changing either the pH of the mobile phase, the temperature of the system, or the type of organic eluent employed. Changes in the analyte ion- ization state were observed upon increasing the acetonitrile composition as well as the temperature. Method development for ionizable analytes...
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Therefore to enhance the retention of this potential degradation product the initial organic composition of the gradient was reduced from 35%. ion of the impurity that has been resolved from the main peak. The mass spectrum of the impurity (RRT 1.04) that has now been resolved from the main peak was also taken. MS conditions flow split 10 : 1....
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The extent to which an organic molecule absorbs electromagnetic radiation in the ultraviolet region (UV light) depends on the structure of the molecule.. The pH of the mobile-phase effects the ionization of ionogenic solutes and also the analyte UV response. The change in pH can change the electronic structure of the molecule and result in changes in the molar absorptivity...
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This lead to the final selection of the most potentially viable therapeutic candidates that are taken forward to drug development. Chromatographic separations are based on a forced transport of the liquid (mobile phase) carrying the analyte mixture through the porous media and the differences in the interactions at analytes with the surface of this porous media resulting in different migration...
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Dynamic transfer of the analyte molecules between mobile phase and adsorbent surface in the presence of secondary equilibria effects is also only part of the processes responsible for the analyte retention on the column. Efficiency is the measure of the degree of peak dispersion in a particular column. as such, it is essentially the characteristic of the column. If H...
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Due to the exponential nature of the rela- tionship between retention and interaction energy even the presence of 1%. Bonding density is the primary parameter in evaluation of the quality of the bonded material. All parameters of the packing material are interrelated in their influence on the chromatographic performance of the column. Macropores in the monolith are between 4000 and...
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At the same time, the pHs of aqueous–organic mixtures are different from the pH of the aqueous compo- nent itself. The basis for the analyte retention in reversed-phase chromatography is the competitive interactions of the analyte and eluent components with the adsor- bent surface. The stronger the interactions of the analyte with the surface, the longer its retention. Selectivity or...
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An empirical formula representing the variation of the δ quantity with mole fraction of acetonitrile (χ) from the values in Table 4-4 could be determined using equation (4-20). It was shown that the s s pH of the eluent increases with an increase of acetonitrile content. The change in the mobile-phase pH of a particular buffer as a function of...
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Figure 4-45 shows the similar retention dependencies of adrenaline retention for different amphiphilic ions adsorbed on the surface of the reversed-phase material, indi- cating that at the same surface concentration of any amphiphilic ion adsorbed, the retention of basic analyte is the same. Comparison of Figures 4-46 and 4-45 indicates that the retention of a charged analyte in ion-pairing mode...
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NORMAL-PHASE HPLC. Among the various modes of HPLC, reversed-phase and normal-phase chromatography (NPC) are employed most commonly in separation. Normal-phase chromatography was the first liquid chromatography mode, discovered by M. In this chapter we describe a simplified overview of the theory and practice of normal-phase chromatography.. 5.2 THEORY OF RETENTION IN NORMAL-PHASE CHROMATOGRAPHY. As the polarity of the mobile phase...
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6.1 SEPARATION OF THE ANALYTE MOLECULES BY THEIR SIZE. The separation process in simplified form is based on the ability of sample molecules to penetrate inside the pores of packing material and is dependent on the relative size of analyte molecules and the respective pore size of the absorbent. The process also relies on the absence of any interactions with...
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Specific require- ments or methodologies for validation depending on the life cycle of the potential drug candidate in each specific area in the drug development process will be addressed in the corresponding chapter.. Quantitative measurements of the content of related substances*. As development of the project progresses and as more analytical and product-specific information is acquired, the analytical methods evolve...
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This includes standard analytical procedures of peak integration, calibration and quantitation, and more complex correlation of the retention dependencies with variation of selected parameters.. Selection of the starting conditions for method development by using information of similar separations. Optimization of the existing method, to speed up the analysis, increase ruggedness of the chromatographic method, and so on. With the present...
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Focus within the pharmaceutical industry has been to increase the likeli- hood of successfully developing clinical candidates by optimizing the compo- nents of the discovery process (i.e., spanning target identification → chemical. Once considered primarily an enabling tool for medicinal chemists, HPLC and LC/MS are now key technologies incorpo- rated at just about every stage of the drug discovery process....
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Lipinski has referred to this analysis as “rule of five” because the cutoffs for each of the four parameters were all close to five or a multiple of five. The absorption of drug molecules in the gastrointestinal tract is dependent upon the pK a of the compound and the pH of the gastrointestinal region (Figure 12-2). Almost 63% of all...