Name: capillary electrophoresis: separation modes
Uploaded: 2024-12-05T18:32:01.000Z
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Capillary electrophoresis separates charged molecules using an electric field within a capillary. It has several modes for diverse applications.
Capillary gel electrophoresis uses a porous gel polymer matrix to separate analytes based on size, making it useful for analyzing biomolecules like DNA and proteins.
In capillary zone electrophoresis, separation occurs based on differences in electrophoretic mobility.
It efficiently separates charged species like inorganic ions, organic acids, amines, and large biomolecules like proteins.
Micellar electrokinetic capillary chromatography separates neutral species based on their partitioning ability into a charged micelle, an aggregation of molecules with ionic heads and hydrophobic tails.
Capillary electrochromatography uses nonpolar stationary phase-packed capillary tubing, allowing neutral species separation through partitioning between the stationary phase and buffer solution.
Capillary isotachophoresis separates cations or anions with analyte bands migrating at the same velocity.
Capillary isoelectric focusing separates amphiprotic species that donate and accept protons using pH gradient buffer mixtures.

capillary electrophoresis: applications

Capillary Electrophoresis: Applications

Capillary electrophoretic separations offer various modes, each with unique applications. These modes include capillary zone electrophoresis, capillary gel electrophoresis, capillary array electrophoresis, capillary isoelectric focusing, capillary isotachophoresis, micellar electrokinetic chromatography, and capillary electrochromatography.
Capillary zone electrophoresis (CZE) separates ionic components based on their electrophoretic mobility. It has been used to separate proteins, amino acids, and carbohydrates in minimum time, making it a major technique in the rapidly expanding field of proteomics. For example, it is used for protein analysis in urine samples to diagnose chronic kidney and coronary artery disease.
Capillary gel electrophoresis (CGE) is performed in a porous gel polymer matrix. It provides a molecular sieving action to separate macromolecules like proteins, DNA fragments, and oligonucleotides that have similar charges but differ in size. CGE plays a significant role in DNA sequencing, particularly in the Human Genome Project.
Capillary array electrophoresis (CAE) operates multiple capillaries in parallel for DNA sequencing. DNA is fragmented and labeled with fluorescent dyes, with the sequence determined by the dye color sequence of the eluting fragments.
Capillary isoelectric focusing (CIF) mode separates amphiprotic species, such as amino acids and proteins that contain weak carboxylic acid and weak-base amine groups. Amphiprotic compounds can donate or accept protons; in amino acids, this amphiprotic behavior results in a zwitterion with both positive and negative charges. The zwitterion does not migrate in an electric field when the solution&#39;s pH equals its isoelectric point (pI), making the pI a key characteristic in separating such molecules. Separations are based on differences in equilibrium properties of the analytes rather than migration rates.
Capillary isotachophoresis (CITP) separation mode focuses on the equal velocity migration of all analyte bands, separating either cations or anions but not both. Analyte ions migrate with unique velocities, forming adjacent bands that ultimately move at the same velocity.
The micellar electrokinetic chromatography (MEKC)&#160; technique overcomes CZE&#39;s limitation of not being able to separate neutral species by adding a surfactant like sodium dodecyl sulfate (SDS) to the buffer solution. The separation mechanism is similar to liquid chromatography (LC), depending on differences in distribution constants between the mobile aqueous phase and the hydrocarbon pseudo-stationary phase. MEKC has been used to separate a wide variety of samples, including mixtures of pharmaceutical compounds, vitamins, and explosives.
An alternative method for separating neutral compounds is capillary electrochromatography (CEC). In CEC, capillary tubes filled with silica particles ranging from 1.5 to 3 mm in size and coated with a nonpolar stationary phase are utilized. The separation of neutral species occurs as they distribute themselves between the stationary phase and the buffer solution, the latter acting as the mobile phase due to electroosmotic flow. The separation process is similar to high-performance liquid chromatography (HPLC), yet it does not require high-pressure pumps. Additionally, CEC offers superior efficiency and reduced analysis times compared to HPLC.
These various modes of capillary electrophoresis offer a versatile range of applications, from separating charged species in CZE to separating neutral species in MEKC and CEC, as well as size-based separations in CGE.

Capillary electrophoretic separations offer various modes, each with unique applications. These modes include capillary zone electrophoresis, capillary ...

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Analytical Chemistry

Unit 1

Principles of Chromatography

KEY TERMS AND CONCEPTS

capillary electrophoresis: separation modes

Capillary electrophoresis uses several separation modes to analyze charged molecules, size-based samples, and even neutral compounds. Each mode works a little differently and is used for different kinds of lab problems. Together, they show why capillary electrophoresis is a flexible tool in analytical chemistry.

Capillary zone electrophoresis (CZE) separates ionic components by their electrophoretic mobility. It can separate proteins, amino acids, and carbohydrates in a short time, so it is an important method in proteomics. It is also used to analyze proteins in urine samples to help diagnose chronic kidney and coronary artery disease.

Capillary gel electrophoresis (CGE) uses a porous gel polymer matrix. The gel acts like a molecular sieve, which helps separate large molecules that have similar charges but different sizes. This mode is used for proteins, DNA fragments, and oligonucleotides, and it has an important role in DNA sequencing, including work from the Human Genome Project.

Capillary array electrophoresis (CAE) uses multiple capillaries running in parallel. It is also used for DNA sequencing. In this method, DNA is fragmented and labeled with fluorescent dyes. The sequence is read from the color pattern of the fragments as they elute.

Capillary isoelectric focusing (CIF) separates amphiprotic species, such as amino acids and proteins. Amphiprotic molecules can donate or accept protons. In amino acids, this behavior forms a zwitterion, which has both positive and negative charges. The zwitterion does not move in an electric field when the pH equals its isoelectric point, or pI. That pI value is key to the separation, because the method depends on equilibrium properties rather than migration rate.

Capillary isotachophoresis (CITP) separates either cations or anions, but not both at once. In this mode, analyte ions migrate with different speeds at first, then form adjacent bands that move at the same velocity. Micellar electrokinetic chromatography (MEKC) solves a different problem. It can separate neutral species, which CZE cannot do, by adding a surfactant such as sodium dodecyl sulfate, or SDS, to the buffer. The separation is similar to liquid chromatography and depends on how the analytes distribute between the mobile aqueous phase and the hydrocarbon pseudo-stationary phase.

MEKC has been used for mixtures of pharmaceutical compounds, vitamins, and explosives. Another method for neutral compounds is capillary electrochromatography (CEC). In CEC, capillary tubes are filled with silica particles and coated with a nonpolar stationary phase. The neutral species separate as they distribute between the stationary phase and the buffer solution, which acts as the mobile phase through electroosmotic flow. CEC works like high-performance liquid chromatography, or HPLC, but it does not need high-pressure pumps. It also offers higher efficiency and shorter analysis times than HPLC.

Capillary Electrophoresis: Separation Modes

capillary-electrophoresis-separation-modes

chromatographic methods: terminology

Chromatography Terms and Peak Analysis

Chromatography is an analytical technique used to separate the parts of a mixture and identify substances in it. It is used in chemistry, biology, environmental science, and pharmaceuticals. The method depends on two phases: the stationary phase, which stays fixed, and the mobile phase, which moves across it and carries the solutes. As the mobile phase travels, each mixture component interacts with the phases in a different way. That difference causes the components to separate. Chromatography...

chromatographic methods: classification

Chromatography Types and Separation Modes

Chromatographic techniques are grouped by the phases they use, how those phases interact, and the way they separate sample components. The mobile phase is usually a liquid or a gas. The stationary phase is usually a solid or a liquid layer on a solid surface. Many chromatography names start with the type of chromatography, then the mobile phase, and then the stationary phase. For example, gas-solid chromatography uses a gas mobile phase and a solid stationary phase. In liquid-liquid...

analyte adsorption and distribution

Chromatography: Polarity and Adsorption

Chromatography separates solutes by how they move between the mobile phase and the stationary phase. In many systems, this transfer happens through sorption, which usually means adsorption. The separation depends strongly on polarity, or the overall dipole moment of a molecule. During chromatography, the solute and the solvent compete for adsorption on the stationary phase. Highly polar compounds and polar solvents tend to adsorb strongly on polar surfaces. This affects how the mixture...

diffusion on chromatography columns

Band Broadening from Column Diffusion

Column diffusion causes band broadening in chromatography columns. When an analyte is added as a narrow band at the top of the column, the solutes begin to separate and spread out. As this happens, the band develops a Gaussian profile, which means the concentration is highest near the center and lower at the edges. Longitudinal diffusion is one reason this spreading occurs. In this process, solute molecules in the mobile phase move from the more concentrated center of the band into the more...

chromatographic resolution

Peak Separation in Chromatography

Peak separation in chromatography depends on how far apart two neighboring peaks appear in a chromatogram. As a solute moves through a chromatographic column, it spreads into a band with a Gaussian shape. The longer the solute stays in the column, the broader that band becomes. This broadening can cause peaks to overlap and reduce separation efficiency. Chromatographic resolution is the measure used to judge that separation. It is the ratio of the difference in retention time or retention...

column efficiency: plate theory

Theoretical Plates in Chromatography Columns

Theoretical plates help explain how chromatography columns achieve good separation. Column efficiency is measured by band broadening, and that efficiency depends on the number of theoretical plates, or N. In plate theory, a column is treated as a continuous series of imaginary plates where solute equilibration happens between the stationary and mobile phases. A higher number of theoretical plates means better column efficiency and stronger separation ability. Plate height affects both band...

column efficiency: rate theory

Chromatography Band Broadening in Columns

Chromatography band broadening in columns explains why separated solute zones spread out as they move through a column. The rate theory of chromatography gives a quantitative way to describe the shape and width of elution bands. These bands follow a Gaussian profile, which means they form a smooth bell-shaped curve as the molecules travel. As a solute moves through the column, it makes many random transitions between the stationary phase and the mobile phase. Its residence time in each phase...

optimizing chromatographic separations

Improving Chromatography Resolution

Chromatography resolution improves when bands stay narrow and the two solutes separate clearly in the column. Good separation often depends on band broadening, plate height, capacity factor, and separation factor. These ideas help explain why some mixtures come apart quickly while others take more time. Band broadening is the spreading of solute bands as they move through the column. When bands spread out, resolution drops. Plate height, or H, is the length needed for one theoretical plate. A...

silica gel column chromatography: overview

silica-gel-column-chromatography-overview

Silica Gel Column Chromatography and Polarity

Silica gel column chromatography separates compounds by polarity using a column packed with silica gel. The silica gel acts as the stationary phase, and the solvent is the mobile phase. As the mixture moves through the column, the compounds separate into distinct bands. Polar compounds tend to bind more strongly to the silica gel. Because of this stronger interaction, they move more slowly through the column. Nonpolar compounds bind more weakly to the silica gel. They usually travel faster...

thin-layer chromatography (tlc): overview

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds by polarity. It uses a polar silica gel plate as the stationary phase. Silica gel is a form of silicon dioxide, and its surface has hydroxyl (OH) groups that can form hydrogen bonds with polar compounds. This affects how strongly a compound sticks to the plate. To start a TLC analysis, a mixture is placed on the starting line with a thin capillary. The bottom of the plate is then set in the mobile phase, which is usually an organic solvent...

gas chromatography: introduction

Gas Chromatography: Separating Volatile Mixtures

Gas chromatography separates and analyzes volatile compounds in a sample. It is used to identify and measure the parts of complex mixtures. This makes GC useful in environmental analysis, pharmaceuticals, and petrochemicals. GC is also called vapor-phase chromatography (VPC) or gas-liquid partition chromatography (GLPC). In the process, the sample is vaporized first. It is then mixed with an inert carrier gas, which acts as the mobile phase and carries the sample through a column. The column...

gas chromatography: types of columns and stationary phases

gas-chromatography-types-of-columns-and-stationary-phases

Gas Chromatography Columns and Polarity

Gas chromatography uses stationary phases to separate and analyze parts of a sample. In GC, the stationary phase can be liquid or solid. Liquid stationary phases are non-volatile, thermally stable, and chemically inert liquids coated on the column. Solid stationary phases are adsorbent particles, such as silica gel or molecular sieves. A sample component must interact well enough with the stationary phase to stay in the column long enough to separate. This idea follows “like dissolves like,”...

gas chromatography: sample injection systems

gas-chromatography-sample-injection-systems

Gas Chromatography: Split vs Splitless Injection

Gas chromatography uses sample injection methods to control how much material enters the column. The sample is first introduced as a vapor plug into the carrier gas stream. This helps produce high efficiency and good resolution. A microsyringe places the sample solution into a heated sample port. The heat vaporizes the sample, and it then mixes with the carrier gas. This step prepares the sample for analysis. Some thermally sensitive samples can be injected directly into the column. In that...

gas chromatography: overview of detectors

Gas Chromatography Detector Types and Uses

Gas chromatography detectors turn chemical properties into signals that appear on a chromatogram. These signals help identify and measure the parts of a mixture. In GC, detectors are often grouped as destructive or non-destructive. A non-destructive detector analyzes a sample without changing or using it up. That means the sample can still be collected after detection for more testing. Thermal conductivity detectors and electron capture detectors are examples of this type. A destructive...

gas chromatography: types of detectors-i

Gas Chromatography Detectors: Choosing the Right One

Gas chromatography uses detectors that respond to different kinds of analytes. The main detectors covered here are the thermal conductivity detector (TCD), flame ionization detector (FID), and electron capture detector (ECD). Each one has a different way of turning a separated compound into a signal. The thermal conductivity detector, or TCD, is the earliest and one of the most widely used GC detectors. It works by measuring changes in the thermal conductivity of the carrier gas. When a sample...

gas chromatography: types of detectors-ii

Specialized Detectors in Gas Chromatography

Gas chromatography uses specialized detectors to identify compounds that general-purpose detectors may miss. These detectors are chosen for specific analytical needs. They can target certain elements, functional groups, or trace analytes with greater precision. Thermionic detectors are selective for organic compounds that contain phosphorus and nitrogen. They are especially sensitive to phosphorus compounds compared with the flame ionization detector, or FID. That makes them useful for...

high-performance liquid chromatography: introduction

high-performance-liquid-chromatography-introduction

HPLC Separation, Columns, and Detection

High-performance liquid chromatography (HPLC) separates, identifies, and quantifies the parts of a complex mixture. It uses high pressure to push a liquid mobile phase through a tightly packed column. The result is a precise separation process that is useful for analyzing many samples. In HPLC, the mobile phase is the liquid solvent that carries the sample through the system. The solvent is chosen for its polarity, or how it interacts with other substances. The polarity index helps guide the...

high-performance liquid chromatography: elution process

high-performance-liquid-chromatography-elution-process

HPLC Solvent Flow and Elution Types

High-performance liquid chromatography (HPLC) uses solvent flow and elution to separate analytes in a column. Elution is the way compounds move through the column and separate because of how they interact with the mobile phase and the stationary phase. These interactions affect retention times, peak shape, and resolution in the chromatogram. Knowing how elution works helps students read chromatographic data and understand how mixtures are separated. HPLC relies on highly pure HPLC-grade...

high-performance liquid chromatography: instrumentation

high-performance-liquid-chromatography-instrumentation

HPLC Parts and How They Work

High-performance liquid chromatography, or HPLC, uses a set of connected parts to separate liquid samples under high pressure. The system begins with mobile phase reservoirs, which are glass bottles that hold the solvents. HPLC-grade solvents are used to keep the mobile phase as pure as possible. A degasser removes dissolved gases from the solvents before they move through the instrument. The solvent then reaches the pump, which sends it into the analytical column. Some systems use a...

high-performance liquid chromatography: types of detectors

high-performance-liquid-chromatography-types-of-detectors

HPLC Detector Choices for Analyzing Solutes

High-performance liquid chromatography (HPLC) uses detectors to analyze solutes as they leave the chromatographic column. The detector recognizes a property of the solute and turns it into an electrical signal. A computer then converts that signal into a graph called a chromatogram, which shows detector response over elution time. HPLC includes several detector types, and each one has strengths and limits based on the analyte and the sensitivity needed. No single HPLC detection method can...

ion-exchange chromatography

Separating Ions with Ion-Exchange Columns

Ion-exchange chromatography separates ions by how strongly they bind to a charged stationary phase. The stationary phase is a cross-linked polymer resin with covalently attached ionic groups. These groups may be positively charged or negatively charged, which creates cation exchangers and anion exchangers. The choice of resin depends on the analyte and the separation needed. A cation exchanger contains a polymeric anion with active cations, while an anion exchanger contains a polymeric cation...

size-exclusion chromatography

Size-Exclusion Chromatography in Protein Analysis

Size-exclusion chromatography separates molecules by size, and it is often used for large molecules such as polymers and biomolecules. It is also called molecular-exclusion chromatography or gel-permeation chromatography. In this method, the stationary phase is made of micron-sized particles or resin beads that contain pores. The two main stationary phases are silica particles and cross-linked polymer resin beads. Both are porous, but their pore sizes can differ a lot. Silica particles are...

supercritical fluid chromatography

SFC for Fast Chemical Separations

Supercritical fluid chromatography (SFC) is a separation method used for compounds that can be hard to analyze with gas chromatography (GC) or liquid chromatography (LC). It is useful for nonvolatile or thermally unstable samples that do not work well in GC and for compounds that do not have the right functional groups for HPLC analysis. SFC combines useful features of both GC and LC while keeping the analysis efficient. SFC uses a supercritical fluid as the mobile phase, most often carbon...

affinity chromatography

Affinity Chromatography for Biomolecule Separation

Affinity chromatography separates and purifies specific biomolecules from a complex mixture. It depends on a highly selective match between an analyte and a binding partner, such as an antibody and an antigen. The binding partner is fixed on the stationary phase, which forms the affinity column. The stationary phase is usually a solid support such as agarose or porous glass beads. The mobile phase helps the analyte bind to the ligand and later helps release it. When a sample passes through the...

electrophoresis: overview

Electrophoresis in Gel and Capillary Formats

Electrophoresis separates charged molecules by making them move in an electric field. It is widely used in biochemistry, molecular biology, and analytical chemistry. The technique can separate complex mixtures of amino acids, nucleotides, carbohydrates, and proteins with strong resolution. Two main formats are used for electrophoretic separations: slab electrophoresis and capillary electrophoresis. Slab electrophoresis uses a gel matrix, such as agarose or polyacrylamide, as a sieve. The pores...

capillary electrophoresis: instrumentation

capillary-electrophoresis-instrumentation

Capillary Electrophoresis: Sample Separation Setup

Capillary electrophoresis uses a high-voltage setup, a capillary tube, a sample vial, and a detector to separate charged molecules. The electric field comes from a power supply connected to an anode and a cathode in buffer reservoirs at each end of the capillary. The capillary is made of fused silica and coated with polyimide for added strength. To start the separation, the sample must be placed inside the capillary. One end of the capillary and its electrode are removed from the buffer...

Capillary electrophoresis uses several separation modes to analyze charged molecules, size-based samples, and even neutral compounds. Each mode works a little differently and is used for different kinds of lab problems. Together, they show why capillary electrophoresis is a flexible tool in analytical chemistry. Capillary zone electrophoresis (CZE) separates ionic components by their electrophoretic mobility. It can separate proteins, amino acids, and carbohydrates in a short time, so it is an...

key terms and concepts

Learn how capillary electrophoresis separates proteins, DNA, amino acids, and neutral compounds using CZE, CGE, CAE, CIF, CITP, MEKC, and CEC.

Capillary Electrophoresis: Separation Modes | JoVE K12

analytical chemistry

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Capillary Electrophoresis: Separation Modes

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