Tìm thấy 20+ kết quả cho từ khóa "stationary phases"
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Apart from the differences in RPC stationary phases described in Sections 5.3.1 and 5.3.2, the chemical composition of the ligand can vary. Functional Groups Found in HPLC Stationary Phases
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rigidity, 679. transient diastereomeric complexes, 675 Chiral stationary phases . macrocyclic antibiotics, 699–705 microcrystalline cellulose triacetate, 682 mobile phase effects, 680–681.
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The next classification step is based on the nature of the stationary phase.. Liquid chromatography was further diversified according to the type of the interactions of the analyte with the stationary phase surface and according to their relative polarity of the stationary and mobile phases.. The relative polarity of the mobile and stationary phases appears to be “reversed” compared to the historically original polar stationary phase and non-polar mobile phase used by M.
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Y (m) and Y (s) refer to a molecule of solute Y in the mobile and stationary phases, respectively, while M (m) and M (s) refer to a molecule of solvent M in the mobile and stationary phases, respectively. The quantity n in Equation (8.1) is thus the ratio of molecular areas for the solute with relation to the mobile phase.. Retention differs for a more-polar mobile-phase solvent such as tetrahydrofu- ran (THF) and a more polar solute such as phenol (Fig.8.3c,d). Mobile phase.
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This situation changed dramatically in the 1960s with the theoretical understanding of the chromatographic process, the development of high-performance liquid chromatography, and the synthesis of highly selec- tive stationary phases.
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In normal-phase chromatography, polar stationary phases are employed and solutes become less retained as the polarity of the mobile-phase system increases. Retention in normal-phase chromatography is predominately based upon an adsorption mechanism. In the future, with the advent of new station- ary phases being developed, one should expect to see increasingly more interesting applications in the pharmaceutical industry..
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The V m and V s are the volume of the mobile and the volume of the stationary phases in the column, respectively. Instant equilibrium of the analyte distribution between mobile and stationary phases is assumed.. The total amount of the analyte in the column cross section dx is distrib- uted between the mobile and stationary phases and could be written in the following form:. (2-42) where df(c)/dc is the derivative of the partitioning distribution function.
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Therefore, our methodology for identifying sRNAs and subsequent cataloguing of their Table 1 Conditional expression of the 24 experimentally validated sRNAs. 3 High expression of the MTS2823. 5 Expression of ncRv11806 in the exponential and stationary phases of growth. sRNA ncRv11806 expression is induced in the stationary phase compared to the exponential growth phase. ncRv11806 lies in the IGR between the genes PE20 and PPE32 (represented as arrows). sRNA ncRv11875C which is flanked by the genes
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X (stationary phase) (2.2) Molecules of X in Figure 2.4 are found equally in the mobile and stationary phase at any time, while molecules of Z predominate in the stationary phase. mobile phase X. Figure 2.4 Equilibrium distribution of solvent and sample molecules between the mobile and stationary phases, and the resulting effect on solute migration rate. Equal amounts of X and Z in the sample are assumed..
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In this technique a polar stationary phase is used with an aqueous-organic mobile phase. In contrast to RPC, the aqueous component of the mobile phase (e.g., water or buffer) serves as the strong solvent and the organic component (usually acetonitrile) is now the weak solvent. 13.25). Note also that retention increases for more polar solutes in Figure 13.25 (Arg [most polar] >. HILIC can be considered as a variant of normal-phase chromatography (NPC. 13.4.4.1 Stationary Phases for HILIC.
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Illustration of the interaction of a nonpolar sam- ple solute with the stationary phase (a) and of a polar solute with the mobile phase (b). of each of the two adjacent atoms. Solute polarizability increases with the size of the molecule (number of atoms or molecular weight) and with refractive index [9]. Because of the nonspecific and universal nature of dispersion interactions, they are significant in both the mobile and stationary phases.
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Striegel, ed., ACS, New York, 2005, ch. 14.1 INTRODUCTION, 666. 14.2 BACKGROUND AND DEFINITIONS Isomerism and Chirality, 667. 14.2.2 Chiral Recognition and Enantiomer Separation, 669 14.3 INDIRECT METHOD, 670. 14.4 DIRECT METHOD, 675. 14.4.1 Chiral Mobile-Phase-Additive Mode (CMPA Chiral Stationary-Phase Mode (CSP), 677. 14.4.3 Principles of Chiral Recognition, 679 14.5 PEAK DISPERSION AND TAILING, 681 14.6 CHIRAL STATIONARY PHASES. 14.6.4 Cyclodextrin-Based CSPs Macrocyclic Antibiotic CSPs Chiral
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In this approach, a single capillary HPLC column consists of successive segments of two orthogonal stationary phases (cation exchange followed by RPC) for the separation of complex peptide mixtures. In a typical elution cycle, a part of the sample is displaced from the cation-exchange segment by aqueous buffer, following which the displaced fraction is eluted from the RPC segment by an acetonitrile-buffer gradient in 90 to 120 minutes. 13.4.5.3 MDLC with Column Switching.
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A more detailed discussion of the stationary phase types and mechanism of interaction and separation theory in relation to chiral compounds is given in Chapter 22. A large number of chiral stationary phases are currently avail- able to meet the needs of the pharmaceutical industry for determination of the enantiomeric purity of active pharmaceutical ingredients, raw materials, and metabolites.
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One of the most important characteristics of the chromatographic column is its resolution, or the ability to separate components with very similar distribution constants between the mobile and stationary phases (KD). Among them, the nature of the stationary phase, mobile phase, temperature, the size of the column, that is, its length (L), inner diameter (ID) and the thickness of the stationary phase (df. Obviously, increasing the length of the column markedly increases the analysis time.
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The allowed cost of this purification step per pound of product was determined, based on expected product sales in the ton-per-year range.. 13.9.2.2 Stationary Phases. The column packing was selected after screening products from five manufacturers..
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It is not- able that all RNAs were expressed in all analysed growth conditions (CRT, NAR and NIT) as well as in the exponential and stationary phases (Fig. However, a small decrease in expression for the Hsnc042 sRNA in the NAR condi- tion in stationary phase and for Hsnc073 sRNA under NAR and NIT conditions in stationary phase was observed.. In addition, we notice that Hsnc073 and Hsnc082 sRNAs showed lengths in the northern blot smaller.
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It is commonly accepted that the desorption process can be slow because of the formation of analyte-selector complexes that are stabilized by simultaneous, multiple interactions. 14.6 CHIRAL STATIONARY PHASES AND THEIR CHARACTERISTICS. Success in the use of enantioselective columns depends on the selection of a suitable CSP—one that is able to separate the target enantiomers. These issues will be covered in the present section..
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Layne, Characterization and comparison of the chromatographic performance of conventional, polar-embedded, and polar-endcapped reversed-phase liquid chromatography stationary phases, J. Rokushika, Retention properties of the fluorinated bonded phase on liquid chromatography of aromatic hydrocarbons, J. Siegel, New chromatographic hydrophobicity index (ϕ 0 ) based on the slope and the intercept of the log k′ versus organic phase concentration plot, J.
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Aside from this peculiar configurational arrangement of the natural alkaloids, the exceptional enantiorecognition capability of the cinchonan carbamate-based chiral stationary phases arises also from several features: the bulky quinuclidine, the planar quinoline ring, and the semi-flexible carbamate group with a bulky t-butyl residue.. Figure 14.28 Commercially available cinchona alkaloid-derived chiral anion-exchangers.