Functional liquid chromatography

Unfortunately, there are many expressions in the literature that give molecular weight as a function of diffusivity, and the most appropriate expression must be identified in order to permit a reasonably accurate value for the molecular weight to be calculated. Thus, the diffusivities of a large number of solutes of known molecular weight need to be measured in a solvent that is commonly used in the liquid chromatography, so that a practical relationship between diffusivity and molecular weight can be identified. 

The principle was demonstrated using triazine herbicides as templates and by varying the type of functional monomer and the monomer composition. With a final batch size of ca. 40 mg of monomer, the consumption of monomers and template is significantly reduced and the synthesis and evaluation can take place in standard high-performance liquid chromatography (UPLC) autosample vials. After synthesis. 

Detectors. The function of the detector in HPLC is to monitor the mobile phase as it emerges from the column. The detection process in liquid chromatography has presented more problems than in gas chromatography there is, for example no equivalent to the universal flame ionisation detector of gas chromatography for use in liquid chromatography. Suitable detectors can be broadly divided into the following two classes ... 

In liquid chromatography, in contrast to gas chromatography [see Section 9.2(2)], derivatives are almost invariably prepared to enhance the response of a particular detector to the substance of analytical interest. For example, with compounds lacking an ultraviolet chromophore in the 254 nm region but having a reactive functional group, derivatisation provides a means of introducing into the molecule a chromophore suitable for its detection. Derivative preparation can be carried out either prior to the separation (pre-column derivatisation) or afterwards (post-column derivatisation). The most commonly used techniques are pre-column off-line and post-column on-line derivatisation. 

The consideration made above allows us to predict good chromatographic properties of the bonded phases composed of the adsorbed macromolecules. On the one hand, steric repulsion of the macromolecular solute by the loops and tails of the modifying polymer ensures the suppressed nonspecific adsorptivity of a carrier. On the other hand, the extended structure of the bonded phase may improve the adaptivity of the grafted functions and facilitate thereby the complex formation between the adsorbent and solute. The examples listed below illustrate the applicability of the composite sorbents to the different modes of liquid chromatography of biopolymers. 

More recently, the reaction advancement of resole syntheses (pH = 8 and 60°C) was monitored using high-performance liquid chromatography (HPLC), 13C NMR, and chemical assays.55,56 The disappearance of phenol and the appearances of various hydroxymethyl-substituted phenolic monomers and dimers have been measured. By assessing the residual monomer as a function of reaction time, this work also demonstrated the unusually high reactivity of 2,6-dihydroxymethyl-phenol. The rate constants for phenolic monomers toward formaldehyde substitution have been measured (Table 7.6). 

In the ED setting, the diagnosis of ketamine intoxication is a clinical one. Ketamine is not routinely detected by urine toxicology tests, although it can be detected with high-performance liquid chromatography (Koesters et al. 2002). As with MDMA, the initial assessment for ketamine intoxication includes the use of routine laboratory tests to detect electrolyte abnormalities and to evaluate renal and hepatic functioning (Koesters et al. 2002). 

The characteristics of an ideal liquid chromatography-mass spectrometry interface have been discussed, with emphasis having been placed upon the major incompatibilities of the two component techniques that need to be overcome to allow the combination to function effectively. 

The structures of many oligosaccharide chains can be elucidated by gas-liquid chromatography, mass spectrometry, and high-resolution NMR spectrometry. Glycosidases hydrolyze specific linkages in oligosaccharides and are used to explore both the structures and functions of glycoproteins. 

This technique is based on the same separation mechanisms as found in liquid chromatography (LC). In LC, the solubility and the functional group interaction of sample, sorbent, and solvent are optimized to effect separation. In SPE, these interactions are optimized to effect retention or elution. Polar stationary phases, such as silica gel, Florisil and alumina, retain compounds with polar functional group (e.g., phenols, humic acids, and amines). A nonpolar organic solvent (e.g. hexane, dichloromethane) is used to remove nonpolar inferences where the target analyte is a polar compound. Conversely, the same nonpolar solvent may be used to elute a nonpolar analyte, leaving polar inferences adsorbed on the column. 

Retention in SFC is a complex function of the experimental parameters and is not as easily rationalized as in the case of gas and liquid chromatography. Retention in SFC is dependent upon temperature, pressure, density, sample concentration, composition of the mobile phase and the composition of the stationary phase. Many of these variables are interactive nd do not change in a... 

The rapid and reversible formation of complexes between some metal ions and organic compounds that can function as electron donors can be used to adjust retention and selectivity in gas and liquid chromatography. Such coordinative interactions are very sensitive to subtle differences in the composition or stereochemistry of the donor ligand, owing to the sensitivity of the chemical bond towards electronic, steric and strain effects. A number of difficult to separate mixtures of stereoisomers and isotopomers have been separated by complexation chromatography. 

Bennett, H.P.J. Browne, C.A. Goltzman, D. and Solomon, S. Isolation of peptide hormones by reverse-phase high pressure liquid chromatography. In Gross, E., and Meinenhofer, J., ed, Pepti des. Structure and Bioloai cal Function. Rockford,... 

Kanda, T., Shirota, O., Ohtsu, Y., and Yamaguchi, M., Synthesis and characterization of polymer-coated mixed-functional stationary phases with several different hydrophobic groups for direct analysis of biological samples by liquid chromatography, /. Chromatogr. A, 722, 115, 1996. 

When the predominant functional group of the stationary phase is more polar than the commonly used mobile phases, the separation technique is termed normal-phase HPLC (NPLC), formerly also called adsorption liquid chromatography. In NPLC, many types... 

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