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MS detection has become the standard detector system for bioanalytical methods—the analysis of pharmaceutical compounds in biological systems (e.g., plasma or urine). MS detectors are also widely used in the R&D setting to provide structural information or confirmation of unknowns, although it does not have the mass-resolution capability of traditional stand-alone mass spectrometers. (Within a given run, more than one...
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Figure 4.37 shows an example of the popular post-column derivatization of amino acids with ninhydrin followed by UV detection at 405 nm. THE COLUMN. 5.1 INTRODUCTION, 200 5.2 COLUMN SUPPORTS, 200. 5.3.2 Other Organic-Based Stationary Phases Column Functionality (Ligand Type), 225 5.4 COLUMN SELECTIVITY, 227. 5.4.2 Column Reproducibility and ‘‘Equivalent’’ Columns Orthogonal Separation, 236. 5.4.4 Other Applications of Column Selectivity,...
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Figure 5.2 Visual appearance of several silica particles for RPC. mobile-phase velocity (mm/sec) 5- μ m totally porous. 3.5- μ m totally porous. 1.8- μ m totally porous. Figure 5.3 Column efficiency as a function of particle size and type. mobile phase is 60% acetonitrile-water mobile phase;. Halo particle-size-distribution Average = 2.77 μ m. Figure 5.4 Narrower particle-size-distribution for the...
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Figure 5.12 High-temperature separation of a pharmaceutical mixture. low- and high-pH mobile phases (1 ≤ pH ≤ 13), and they can be used at very high temperatures. Figure 5.12 shows a separation on a zirconia column at pH-13 and 140 ◦ C. Early columns packed with polymer-coated zirconia displayed rather poor efficiency, apparently because of poor stationary-phase mass transfer.. Consequently,...
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Phenyl columns Cyano column “Other”columns. Figure 5.19 RPC columns classified according to the ligand (figures omit the connecting silane group [–Si(CH 3 ) 2. simplified cartoons of Figure 5.19 (the—Si[CH 3 ] group is omitted in Fig. 5.19d), and this gives rise to the additional column types listed at the bottom of Figure 5.19. The nature of the ligand mainly...
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236 THE COLUMN. Values of H 1 and H 2 refer to values of H for columns 1 and 2, and similarly for the remaining column parameters S*, A, etc. A value of F s ≤ 3 indicates that the two columns are similar in selectivity and can be substituted for each other in any RPC separation (for less challenging...
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‘‘bad’’ column can be confirmed as the cause of the problem.. Every column used for a routine method has a finite lifetime (number of injected samples before column failure) that depends on separation conditions—especially mobile-phase pH and temperature. The performance and life of the column depend on how it is used and handled.. column, or deterioration of the column packing....
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Beginning in the early 1970s, RPC columns of the latter type were used increasingly because of their many advantages. In the mid-1970s, the use of RPC underwent an explosive growth in popularity. several hundred separations are cited in [5] for the period 1976 to 1979. samples, the classic paper by Horv ´ath [6] demonstrated that RPC could also be used...
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A 1:1 blend of the mobile phases of Figure 6.8a (46% ACN) and Figure 6.9a (61% MeOH) was prepared, and used to obtain the separation of Figure 6.9b. Figure 6.7 Variation of log k with %B for regular and irregular samples. (c) irreg- ular sample of Figure 6.6. conditions as in Figure 6.6. While the separation of Figure 6.9b is...
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We presently have a more complete understanding of the basis of column selec- tivity than for other kinds of selectivity (solvent strength, solvent type, temperature, etc. As discussed in Section 5.4.1, column selectivity can be quantitatively defined by five different characteristics:. For the case of neutral samples, only the first four column parameters (H, S*, A, B) are important. The...
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RPC (Chapter 6, or Section 7.3) IPC (Section 7.4) IEC (Section 7.5) NPC (Chapter 8). Adjust column conditions (N, Section 2.5.3) Figure 6.21 (Continued). can be varied (step 6) for the purpose of either increasing resolution or reducing run time.. Multiple-variable optimization in each case relies on an experimental design: a plan for the required experiments, as illustrated in Figure...
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mobile phase is 30% ACN-buffer for (a) and (b). 8% chloroform-ACN mobile phase. From a practical standpoint, if NARP is chosen for a separation, all water must be washed from the HPLC system and column prior to switching to the nonaqueous mobile phase.. Solutes that are very polar may not be retained with k ≥ 1, even when pure water...
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Figure 7.1 Hypothetical illustration of the RPC separation of an acidic compound HA from a basic compound B as a function of pH. (a) Ionization of HA and B as a function of mobile-phase pH and effect on k. (b) sample separation as a function of mobile-phase pH;. Figure 7.1b shows chromatograms for the separation of HA and B as...
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Phosphate buffers have been preferred for this application, as long as the mobile-phase pH can be accommodated within the ranges specified in Table 7.1 (pH pH ≤ 8.5, or pH ≥ 11.0). Phosphate, acetate, and formate are the most commonly used buffers for separations with a mobile-phase pH <. 8) as a result of the development of RPC columns that...
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Conditions that are less used today for the control of RPC selectivity include:. Buffer type is not commonly considered as a means of controlling selectivity for the separation of ionic samples. As discussed in Section 7.2.3, however, buffer type can affect the ‘‘effective’’ pK a of a solute, which is equivalent to a change in pH. 6 and/or older, type-A...
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For examples of these generalizations, see the discussion of Figure 7.12 in the following section.. It is possible to continuously vary the nature of retention, from RPC retention as in Figure 7.11a to IPC retention as in Figure 7.11b, by varying the concentration of the IPC reagent in the stationary phase. The concentration of the reagent in the stationary phase...
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346 IONIC SAMPLES: REVERSED-PHASE, ION-PAIR, AND ION-EXCHANGE CHROMATOGRAPHY. pH-2.5 phosphate buffer plus 2-mM octane sulfonate IPC reagent. if IPC separation is chosen, choose an IPC reagent and its initial concentra- tion as described in Section 7.4.2.1.. A prior knowledge of the composition of the sample, or previous exper- iments where pH is varied (step 3) should indicate the choice of...
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Figure 7.21 Separation of a mixture of carbohydrate standards by anion-exchange chro- matography with amperometric detection. Mixed mode 1-3. Figure 7.22 Separation of a nitrogen-mustard mixture by RPC (a) versus mixed-mode IPC (b). Figure 7.23 Separations of a mixture of acids, bases, and three amino acids by means of different columns. column, a commercial mixed-mode column (hydrophobic cation-exchanger), and the...
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Isomeric solutes are usually much better separated by NPC than by RPC, as seen in Figure 8.2b (C 1 or methyl-substituted anilines), Figure 8.2c (C 2 or dimethyl- plus ethyl-substituted anilines), and Figure 8.2d (C 3 or trimethyl-, methylethyl-, and n-propyl-substituted anilines). The greater isomer-selectivity of NPC versus RPC is also shown by the range in values of k for...
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The detection of sample bands in TLC as in Figure 8.8 normally requires the addition of a visualization agent to the plate. Changes in retention order as a result of a change in separation conditions can be quite pronounced when NPC is used with a silica column—often much more so than in RPC. This ability to exert a greater control...