Electrolyte buffer

Figure 50-2. Technique of cellulose acetate zone electrophoresis. A A small amount of serum or other fluid is applied to a cellulose acetate strip. B Electrophoresis of sample in electrolyte buffer is performed.

It is very often necessary to characterize the redox properties of a given system with unknown activity coefficients in a state far from standard conditions. For this purpose, formal (solution with unit concentrations of all the species appearing in the Nernst equation its value depends on the overall composition of the solution. If the solution also contains additional species that do not appear in the Nernst equation (indifferent electrolyte, buffer components, etc.), their concentrations must be precisely specified in the formal potential data. The formal potential, denoted as E0, is best characterized by an expression in parentheses, giving both the half-cell reaction and the composition of the medium, for example E0,(Zn2+ + 2e = Zn, 10-3M H2S04). 

In principle, each solution can be independent, composed of different solvents, reactants, electrolytes, buffers, and additives. However, aqueous solutions have been used for the most part, as their electrochemical behavior is better understood, and ultra pure water can be obtained by a number of methods. 

Figure 3.7 contains an illustration of the basic components of a typical electrophoresis apparatus. The troughs at either end contain an electrolyte buffer solution. The sample to be separated is placed in the approximate center of the electrophoresis strip. 

FIGURE 1.16 Electropherogram of a Passiflorae herba methanol extract. Capillary temperature 35°C voltage 30 kV electrolyte buffer 25 mM sodium tetraborate containing 20% MeOH (pH 9.5) UV detection at 275 nm IS internal standard quercetin 3-0-arabinoside. (From Marchart, E., Krenn, L., and Kopp, B., Planta Med., 69, 452, 2003. With permission.)... 

FIGURE 13.19 CE/ESI-MS electropherogram for the analysis of three selenium species (SeM, SeC, and SeCM) using 5% acetic acid as electrolyte buffer. The insets give information about the isotopic patterns of the species. (Reprinted from Michalke et al. 1999 Fresenius J. Anal. Chem. 363 456-459.)... 

C. Electromigration Dispersion Electromigration dispersion manifests itself in the form of either fronting or tailing peaks, as shown in Figure 4.8. The peak shapes occur as a result of conductivity differences between the analyte zones and the carrier electrolyte (buffer). Conductivity differences... 

Each end of the capillary tubing was dipped into a 4-mL glass vial containing approximately 3 mL of electrolyte-buffer solution. 

Raw materials in Solution The types of raw materials used to be part of solutions are presented in Table l.They have different purposes and can be cosolvents, electrolytes, buffers, antioxidants, preservatives, coloring, flavoring and sweetener agents, among others. 

To carry out a comparison of HPLC and CE, the effects of varying the parameters common to the two techniques with the greatest impact on the separation processes were evaluated. These were pH of the mobile phase and electrolytes, buffer concentration, and temperamre, with the gathered data compared in each case. 

Different types of EKC have been developed. Cy-clodextrins (CDEKC) have been used to form inclusion complexes with solutes to effect their separation. Other examples of EKC include microemulsion electrokinetic chromatography (MEEKC). The MEKC technique (for a detailed treatise, the reader is referred to Ref. 4) utilizes the presence of micelles in the electrolyte buffer solution to influence the migration time of solutes. In this case, the separation carrier is the micelle [5]. 

Isoelectric focusing was carried out in a temperature gradient from -40°C (lower cathode) to +30°C (higher anode) during 20 hours with a potential of 1500 V and an initial current of 4.5 mA. The electric field was 75 V cm-1. The conductance of the electrolyte buffer in mixed solvent, measured at room temperature both before and after the experiment, was 450 /xft-1. 

The ionic strength p, of an electrolyte (buffer) composed of monovalent ions is equal to its molarity (mol/L). The ionic strength of a 1 mol/L electrolyte solution with one monovalent and one divalent ion is 3 mol/L, and for a doubly divalent electrolyte, it is 4 mol/L. 

Another analytical sensor that is based on the electrolytic reduction of O2 has been commercialized during the past decade. This is a device for the rapid, accurate assay of glucose in human blood and makes use of an immobilized enzyme (glucose oxidase) on a disposable sample probe that includes an O2-electrolysis sensor with electrolyte, buffer, and various inhibitors. When a drop of blood is placed on the sample probe, the glucose oxidase (GO) transformation of the glucose begins via the reduction of the ambient O2 to HOOH. 

Table 2.1 presents an overview of factors that can potentially be considered for optimization and robustness testing of CE methods. Lists of commonly used electrolytes/buffers (20-23) or additives (20) and characteristic properties of frequently applied solvents and surfactants (20) can be found in the literature. Sample concentration (see Table 2.1) is a factor occasionally included. However, the aim of the analytical method is to estimate this concentration through the measured signal, from a calibration procedure. In method optimization, responses related to the quality of the separation, for example, resolutions, are considered, and in this situation one can verify whether the sample... 

CZE, also referred to as free solution capillary electrophoresis (FSCE), or open tubular capillary electrophoresis (OT CE), is the format originally described, in which the capillary is filled with an electrolyte buffer solution. In CZE, molecules are separated directly according to their charge, and inversely according to their solution drag force. Neutral molecules are moved through the capillary by the EOF. There are many additives which can be used to either dynamically deactivate the fused capillary waU, and prevent undesirable solute sticking, or to enhance solute selectivity, or both. 

In the classic semi-manual electrophoretic technique used mainly in bioanalysis, a small slab or strip of plastic material covered by a porous substance (a gel) is impregnated with an electrolyte buffer. The two extremities of the covered gel system are dipped into two independent reservoirs containing the same electrolyte and linked to the electrodes of a continuous voltage supply (Eigure 8.1). The sample is deposited in the form of a transverse band, which is cooled and then bedded between two isolating plates. Under the effect of several parameters that... 

This mode of electrophoresis, in which the electrolyte migrates through the capillary, is the most widely used. In this mode, samples are applied as a narrow band that is surrounded by the electrolyte buffer. This electrolyte can be, depending upon the application, acidic (phosphate or citrate) or basic (borate) or an amphoteric substance (a molecule possessing both an acidic and an alkaline function). The electro-osmotic flow increases with the pH of the liquid phase or can be rendered inexistent. This procedure is also called, in contrast to CGE (cf. Section % A3), free solution electrophoresis. 

For capillary zone electrophoresis the electrical and thermal detection modes have insufficient sensitivity. This is because in capillary zone electrophoresis there is a relatively large background of supporting electrolyte (buffer) upon which a low concentration of sample ion is superimposed. Detecting the exceedingly small changes in electrical properties or temperature associated with sample zones is difficult. Thus UV absorption and fluorescence detection have been of greatest use in capillary zone electrophoresis. 

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