Vacancy peak method

Several variants of separation methods based on dialysis, ultrafiltration, and size exclusion chromatography have been developed that work under equilibrium conditions. Size exclusion chromatography especially has become the method of choice for binding measurements. The Hummel-Dreyer method, the vacancy peak method, and frontal analysis are variants that also apply to capillary electrophoresis. In comparison to chromatographic methods, capillary electrophoresis is faster, needs only minimal amounts of substances, and contains no stationary phase that may absorb parts of the equilibrium mixture or must be pre-equilibrated. 

Fig. 1 Schematic representation of the experimental setups of the mobility-shift method and the Hummel-Dreyer method (A) the vacancy peak method and the vacancy affinity capillary electrophoresis method (B) the equilibrium-mixture method and the frontal analysis method (C) for drug-protein binding analysis. drug protein gg drug-protein complex Q buffer. (Reprinted with permission from Ref. 38. Copyright 1992 Elsevier Science.)...

Kraak et al. (38) reported the first ACE application to study drug binding to a plasma protein. They used the model system warfarin-human serum albumin (HSA) to compare the suitability of the Hummel-Dreyer, frontal analysis, and vacancy peak methods. A more methodologically intended paper from Erim and Kraak (39) used VACE to study the displacement of warfarin from bovine serum albumin (BSA) by furosemide and phenylbutazone. They concluded that VACE is especially suited to examining competitive properties of simultaneously administered compounds toward a given protein-drug system. 

It is well known that drugs bind to plasma proteins, particularly to serum albumin and a-acid glycoprotein, and that only the unbound, or free, fraction is responsible for any pharmacological effect. For protein-drug binding studies size-exclusion chromatography in one of three variants—namely, the Hum-mel-Dreyer method (1962), the vacancy peak method (Sebille, et al., 1979), and frontal analysis (Cooper and Wood, 1968)—is the traditional method of... 

Although affinity capillary electrophoresis (ACE) in its classical mode (one of the reagent is dissolved in a BGE, another is injected) is the most widely used technique in the literature, other capillary electrophoretic methods exist which are even more favorable concerning the information about binding parameters obtainable the Hummel-Dreyer (HD) method, frontal analysis (FA), the vacancy peak (VP) method, and vacancy affinity capillary electrophoresis (VACE) (see, e.g., Refs. 49-57). All the methods need as a precondition that the equilibrium between the reactants (say, protein P, drug D, and complex formed PD) is established rapidly compared to the dislocation of the electropho-retically migrating zones. The experimental setup of the HD and the ACE methods is identical, and so is the setup for the VP and the VACE methods. FA differs from all the other techniques. 

Figure 8.12 Schematic representation of the vacancy peak capillary zone electrophoresis method. Zone identification as in Figure 8.11. (From Kraak et al., 1992, with permission.)...

Concentration pulse chromatography (also called elution on a plateau, step and pulse method, system peak method, or perturbation chromatography) is experimentally much simpler [100,103,104]. The same experimental procedure is used as for the determination of smgle-component isotherms. First, the column is equilibrated with a solution of the multicomponent mixture of interest in the mobile phase. When the eluent has reached the composition of the feed to the column, a small pulse of the pure mobile phase (vacancy) or of a solution having a composition different from that of the plateau concentration (see end of this section) is... 

A blank control run was performed by injection of the above buffer. Then, at the same eluent composition, vacancy peaks were obtained by injection of the above sample solutions containing only HSA in the buffer. Blank and protein injections were run using the eluents containing different drug concentrations (0.4-50 pM) in an automated sequence, controlled by the workstation. The experimental data obtained by the modified Hummel-Dreyer method were analyzed using Scatchard plots. Binding affinity was calculated from a Langmuir-type equation. 

Vacancy chromatography is a special method of development that can provide both negative and positive peaks in the chromatogram. It is not commonly used, although... 

Vacancy Chromatography. One way to use a UV detector for analytes that do not absorb is to include a UV absorber as part of the mobile phase. When the non-UV absorbing analytes enter the detector cell, they cause a decrease in the baseline absorbance, appear as negative peaks, and can be used for routine analysis. In effect, they produce a vacancy hence the name for this method of detection. 

In the present work, the theoretical XANES spectrum for Ce02 is calculated with the DV-X(x method and the peaks therein are assigned to states which are analyzed with wavefunctions, emphasizing the local structural effects. As an application of the present method and the peak assignment, it is clarified how oxygen vacancy affects the spectra for cerium oxides. 

A general mathematical treatment of system peaks and of the closely related method of vacancy chromatography was given by Helfferich and Klein [8]. This work includes a detailed analysis of the phenomena that take place upon injection of a sample into a chromatographic column. It is based on the use of the solution of the ideal model of chromatography for multicomponent systems, with competitive Langmuir isotherms (see Chapters 8 and 9), and of the ft-transform. 

We have developed a novel method for synthesis of hexagonal ZnO microtubes. In this paper, the luminescence characteristics of the ZnO microtubes were investigated based on the analyses of XPS. The surface features, such as oxygen vacancies, surface bonding and surface adsorption, will have significant effects on the luminescence properties. The orange emission and red emissions of the ZnO microtubes are found, although the intensity of emission peaks is weak. 

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