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The hydrophobicity (and therefore retention) of a polypeptide is heavily dependent on the ionization state of the amino-acid termini (approximate pK a values of 2.4 and 9.8) and of the ionizable side chains of internal residues (pK a values in Fig. Thus the pH of the mobile phase can have a profound effect on polypeptide retention, and it is necessary...
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other column lengths, diameters and par- ticle sizes can be used, in which case gradient time and flow rate should be adjusted to maintain similar values of k ∗ with acceptable pressure drop. b Higher temperatures (e.g C) can be desirable for some protein samples, especially those with M >. Figure 13.10, the initial four runs a –d can be...
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Figure 13.19 Steps in the use of IMAC. Adapted from [56].. amino-acid side chains in the protein can form coordination complexes with metals, so IMAC is a general method for protein separation. the strength of metal binding by different amino-acid groups in the protein molecule decreases in the following order:. Cysteine residues can bind metals, but they may not be...
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anion-exchange conditions, the negative charge of a single phosphate group is insufficient to counteract the electrostatic repulsion of N-terminal and side-chain amines, and monophosphorylated peptides elute in or near the void volume. When a weak anion exchange column is operated in the ERLIC mode with higher %-ACN, hydrophilic interaction drives an increased interaction of phosphates, enabling the retention and resolution...
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Figure 13.34 Isocratic HILIC separations of a homologous mixture of. 13.6.2 Ion-Moderated Partition Chromatography. Resins with a low percentage of cross-linking are preferred, in order to allow penetration of the oligosaccharides into the packing. Figure 13.35 shows the separation of oligosaccharides in a corn syrup. For monosaccharides, ligand exchange of the sugar hydroxyls with the fixed counter-ion on the resin...
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The porosity of an SEC column can be characterized by its phase ratio (V i /V 0. as in Figure 13.39a. As particle pore-diameter and pore-volume increase, the mechanical strength of the support decreases.. 13.8.2.3 Particle Diameter. Column packings with particle diameters of 10 to 12 μm are available for less demanding applications, such as preparative separations, while SEC packings...
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Figure 13.45 Preparative separation of rh-insulin. and 4.4–5.4 C-Vs plus recovered solvent from column regeneration) contained an additional 15% of the product (for re-separation)—for an overall insulin recovery of 97%. The initial purity of the sample for RPC separation was 91.5%. 13.9.2.9 Scale-Up. Scale-up experiments were carried out next, using six, successively larger, axial-compression columns, with the bed-volume increased from...
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13.10.3.5 Chemical Composition as a Function of Molecular Size. A copolymer typically exhibits both molecular-weight and chemical-composition distributions. Depending on polymerization conditions, the chemical composition may or may not vary with polymer molecular weight. To investigate the presence of such chemical heterogeneity, we can couple SEC with a spectroscopic technique that yields chemical-composition information. Although information about chemical composition as...
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14.7.2 Thermodynamics of Direct Chromatographic Enantiomer Separation, 716. 14.7.3 Site-Selective Thermodynamics, 717. 14.1 INTRODUCTION. that is, separations that can be used for many different kinds of samples. Usually method development can be started with any of various columns or conditions, and resolution is then systematically improved by varying separation conditions. Furthermore, in most cases, the selection of the column is...
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Mobile phase. Figure 14.8 Equilibria for the retention of R- and S- enantiomers (chiral–mobile-phase addi- tive, CMPA) mode. distribution of the complexed solutes X. X can complex directly with the CMPA in the stationary phase (via processes i and j in Fig. The same equilibria have to be considered for the S-enantiomer (S)-X. The consequences of Figure 14.8 can be...
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If the mobile phase is changed, sufficient equilibration time should be allowed to ensure the complete removal of the polar solvent. In order to achieve reproducible results, when switching from an additive-free to an additive-containing mobile phase (e.g., 0.1% trifluoroacetic acid or diethylamine), and vice versa, a prolonged equilibration time may be required [55].. In rare cases the use of...
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Figure 14.16 Separation of propranolol enantiomers on a protein column (cellobiohydro- lase I. extreme conditions, can easily lead to chemical or biochemical changes of the protein selectors. Another disturbing limitation is a low to moderate column efficiency, as seen in the example separation of Figure 14.16 (N = 300–700). 14.16), low plate numbers, combined with peak tailing, can make the...
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14.6.6 Chiral Crown-Ether CSPs. Stereoselective CSP-analyte complexation with chiral crown-ether CSPs and their first application as CSPs were pioneered by Cram and coworkers [127]. In this early work, two 1,1 -binaphthyl units were incorporated into a crown ether as replacement elements of two ethylene groups of the well-known 18-crown-6.. Structural analogues of such 1,1 -binaphthyl-derived chiral crown-ether based CSPs were...
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Further manipulation of Equation (14.3) provides two additional relationships:. K i,S = −R · T · ln α (14.5) That is, plots of ln K i against 1/T are predicted to be linear, with a slope that is proportional to H 0 i . 14.7.2 Thermodynamics of Direct Chromatographic Enantiomer Separation If a single type of (enantioselective) solute-selector interaction is...
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15.1 INTRODUCTION. A closely allied separation technique, supercritical fluid chromatography [1], is beyond the scope of the present chapter.. 15.1.1 Column Overload and Its Consequences. Prep-LC involves mass-overload conditions, that is, sample weights that are large enough to affect peak widths and retention times. When developing an analytical separation, care is usually taken to ensure that the weight (or volume)...
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this can lead to degradation of the product. NPC is also often favored by a potentially larger value of the separation factor α, which corresponds to larger allowable sample weights (as in the example of Figure 15.2. RPC is not ruled out for prep-LC separation, as there are several options for the recovery of solvent-free product—depending on the nature of...
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Figure 15.9 Isocratic separation of a two-component sample as a function of sample size.. If there is any doubt as to the identity of the product peak in these initial separations, this can be confirmed by a separate injection of pure product.. Step 2 of Figure 15.8. Following the adjustment of %B in step 1, separation conditions are varied for...
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SAMPLE PREPARATION. 16.1 INTRODUCTION, 758 16.2 TYPES OF SAMPLES, 759. 16.3 PRELIMINARY PROCESSING OF SOLID AND SEMI-SOLID SAMPLES, 760. 16.3.1 Sample Particle-Size Reduction Sample Drying, 762. 16.3.3 Filtration, 763. 16.4 SAMPLE PREPARATION FOR LIQUID SAMPLES, 764 16.5 LIQUID–LIQUID EXTRACTION, 764. 16.5.1 Theory Practice Problems, 768. 16.5.4 Special Approaches to Liquid– Liquid Extraction, 770 16.6 SOLID-PHASE EXTRACTION, 771. 16.6.1 SPE and...
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16.5.1 Theory. The Nernst distribution law states that any species will distribute between two immiscible solvents so that the ratio of the concentrations remains constant.. (16.1) where K D is the distribution constant, C o is the concentration of the analyte in the organic phase, and C aq is the concentration of the analyte in the aqueous phase.. For one-step...
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16.2c) permits the handling of submicroliter amounts of sample, such as biological fluids. Solid-phase extraction (SPE) has been performed with various packings that are placed in the pipette tip, or embedded in, or coated on the internal walls of the tip. With coatings on or embedded in the internal surface of the tip, liquid samples can be drawn up and...