Capillary electrophoresis buffer selection

As in HPLC, the coupling of MS detection with CE has provided an excellent opportunity for more selective analysis, but the much reduced flow rates, small injection volumes, limitations in the types of buffers used [since electrospray ionization (ESI) is used in capillary electrophoresis/mass spectrometry (CE/MS)], and need to... 

In practice isotachophoresis is usually performed in narrow tubes with electrodes at either end and is one form of capillary electrophoresis. For the separation of a particular type of ion, e.g. an anion, two buffered electrolyte solutions are selected that have different anions but a common cation with a buffering capacity. One of the anions (termed the leading electrolyte) should show a greater mobility than the other anion and occupies the anodic end of... 

Fused silica capillaries are almost universally used in capillary electrophoresis. The inner diameter of fused silica capillaries varies from 20 to 200 pm, and the outer diameter varies from 150 to 360 pm. Selection of the capillary inner diameter is a compromise between resolution, sensitivity, and capacity. Best resolution is achieved by reducing the capillary diameter to maximize heat dissipation. Best sensitivity and sample load capacity are achieved with large internal diameters. A capillary internal diameter of 50 pm is optimal for most applications, but diameters of 75 to 100 pm may be needed for high sensitivity or for micropreparative applications. However, capillary diameters above 75 pm exhibit poor heat dissipation and may require use of low-conductivity buffers and low field strengths to avoid excessive Joule heating. 

Bonato and Paias [136] developed two sensitive and simple assay procedures based on HPLC and capillary electrophoresis for the enantio-selective analysis of omeprazole in pharmaceutical formulations. Racemic omeprazole and (S)-omeprazole were extracted from commercially available tablets using methanol-sodium hydroxide 2.5 mol/1 (90 10). Chiral HPLC separation of omeprazole was obtained on a ChiralPak AD column using hexane-ethanol (40 60) as the mobile phase and detection at 302 nm. The resolution of omeprazole enantiomers by capillary electrophoresis was carried out using 3% sulfated /1-cyclodextrin in 20 mmol/1 phosphate buffer, pH 4 and detection at 202 nm. 

The key operational parameter in free-solution capillary electrophoresis is the pH of the running buffer, as the electroosmotic flow and ionization of the analyte can be regulated by this variable. The role of buffers in capillary electrophoresis has been discussed in detail, with emphasis on buffer concentration, buffer type, and pH effects [10]. The effect of organic solvents on separation and migration behavior has been studied for dipeptides [11] and somatostatin analog peptides [12]. The order of migration as well as the selectivity may be manipulated by organic modifiers in... 

The major concerns that are general to the use of all capillary electrophoresis systems for the separation of proteins and their building-block components are (a) choosing columns (b) buffer solution compatibility with the system and (c) the selection of the hardware. 

The same authors also applied capillary electrophoresis to the study of benazepril hydrochloride and several angiotensin-converting enzyme inhibitors [43]. Separation of the compounds was performed by means of two phosphate buffers (each 0.1 M) at pH 7 and 6.25, respectively [42], Due to the highest selectivity of the first mentioned running buffer, the same system has been applied for the quantification of benazepril and other compounds in their corresponding pharmaceutical formulations. It was found that the possibility of simultaneous identification and quantification of the active ingredient in the finished products was especially attractive, and that excipients do not adversely affect the results. This article deals with the validation of some parameters of the quantitative analysis, namely linearity, precision, accuracy, and robustness [43],... 

An off-line approach that is simple and useful for peptide/protein sequencing using 5-10 picomoles of material has been demonstrated. Peptide and protein samples were first separated by capillary electrophoresis. Selected peaks were fraction collected and analyzed by both nano-electrospray mass spectrometry and Edman sequencing. A standard peptide mixture, a tryptic-digested protein and intact proteins were used to illustrate this method. Successful fraction collection of each component required reproducible electropherograms, the ability to automatically switch the outlet buffer vessel and the ability to maintain electrophoretic integrity while eluting a peak of interest into a small outlet buffer... 

Buffer Type and Concentration Effect on Mobility Selectivity, and Resolution in Capillary Electrophoresis... 

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. 

Capillary electrophoresis (CE) has emerged as an efficient and rapid separation technique in recent years. Its high efficiency has been employed in many applications such as in the analysis of environmental pollutants.Different approaches have been adopted to enhance selectivity for the analysis of different types of compounds. There are two approaches most commonly used to improve CE separations the addition of modifiers into the electrophoretic medium and the modification of the column. Examples of the first approach include the addition of surfactants into the electrophoretic medium as in micellar electrokinetic chromatography (MEKC), and the use of organic solvents,cyclodextrines, " " or bile salts " as buffer modifiers. Examples of the second method include the use of gel-filled columns (capillary gel electrophoresis) " and the coating of the capillary wall surface. " " ... 

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