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Tag Archives: separation
Incorporating a Separation Into a Flow Injection Analysis
Dialysis and gaseous diffusion are accomplished by placing a semipermeable membrane between the carrier stream containing the sample and an acceptor stream. Shown here is a flow injection manifold incorporating a semipermeable membrane. The smaller green solutes can pass through the … Continue reading
Posted in Illustration
Tagged dialysis, extraction, FIA, flow injection, liquid-liquid extraction, LLE, separation
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Capillary Electrochromatography
Another approach to separating neutral species is capillary electrochromatography, CEC. In CEC the capillary tubing is packed with 1.5–3 μm particles coated with a bonded stationary phase. Neutral species separate based on their ability to partition between the stationary phase … Continue reading
Posted in Illustration
Tagged capillary electrochromatography, CEC, electrophoresis, separation
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Micellar Electrokinetic Capillary Chromatography
One limitation to capillary electrophoresis is its inability to separate neutral species. Micellar electrokinetic capillary chromatography, or MEKC, overcomes this limitation by adding a surfactant, such as sodium dodecylsulfate (a) to the buffer solution. Sodium dodecylsulfate, or SDS, has a … Continue reading
Reversed Migration in Capillary Electrophoresis
We can reverse the direction of electroosmotic flow in capillary electrophoresis by adding an alkylammonium salt to the buffer solution. As shown in (b), the positively charged end of the alkyl ammonium ions bind to the negatively charged silanate ions … Continue reading
Posted in Illustration
Tagged capillary electrophoresis, electroosmotic flow, electrophoresis, separation
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Stacking of Cations and Anions in Capillary Electrophoresis
When a analyte’s concentration is too small to detect reliably, it may be possible to introduce it in a manner that increases its concentration in the capillary tube. This method of injection is called stacking. Stacking is accomplished by placing … Continue reading
Posted in Illustration
Tagged capillary electrophoresis, electrophoresis, separation, stacking
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UV/Vis Detectors for Capillary Electrophoresis
Most of the detectors used in HPLC also find use in capillary electrophoresis. Among the more common detectors are those based on the absorption of UV/Vis radiation, fluorescence, conductivity, amperometry, and mass spectrometry. Whenever possible, detection is done “on-column” before … Continue reading
Posted in Illustration
Tagged capillary electrophoresis, detector, electrophoresis, separation, UV/Vis
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Instrumentation for Capillary Electrophoresis
The basic instrumentation for capillary electrophoresis is shown here and includes a power supply for applying the electric field, anode and cathode compartments containing reservoirs of the buffer solution, a sample vial containing the sample, the capillary tube, and a … Continue reading
Posted in Illustration
Tagged capillary electrophoresis, capillary tube, electrophoresis, Joule heating, separation
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Total Mobility of Solutes in Capillary Electrophoresis
In capillary electrophoresis we inject the sample into a buffered solution retained within a capillary tube. When an electric field is applied across the capillary tube, the sample’s components migrate as the result of two types of action: electrophoretic mobility, … Continue reading
Electroosmotic Flow
When an electrical field is applied to a capillary filled with an aqueous buffer we expect the buffer’s ions to migrate in response to their electrophoretic mobility. Because the solvent, H2O, is neutral we might reasonably expect it to remain … Continue reading
Posted in Illustration
Tagged electroosmotic flow, electrophoresis, hydrodynamic flow, separation
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Ion-Exchange Chromatography
In ion-exchange chromatography (IEC) the stationary phase is a cross-linked polymer resin, usually divinylbenzene cross-linked polystyrene, with covalently attached ionic functional groups. As shown here for a styrene–divinylbenzene co-polymer modified for use as an ion-exchange resin, the ion-exchange sites—indicated here by … Continue reading