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Questions and Answers
In adsorption chromatography employing a polar stationary phase, which mobile phase adjustment would likely decrease the retention time of a polar analyte?
In adsorption chromatography employing a polar stationary phase, which mobile phase adjustment would likely decrease the retention time of a polar analyte?
- Increasing the proportion of a polar modifier in the mobile phase. (correct)
- Lowering the temperature of the chromatographic system.
- Saturating the mobile phase with a non-volatile buffer salt.
- Decreasing the proportion of a nonpolar modifier in the mobile phase.
Why are adsorption chromatography adsorbents important?
Why are adsorption chromatography adsorbents important?
- They catalyze the reaction between the sample and the mobile phase.
- They selectively bind components of a mixture, facilitating separation. (correct)
- They control the flow rate of the mobile phase, ensuring optimal separation.
- They prevent the mobile phase from mixing with the stationary phase.
How does the elutropic strength of a mobile phase influence analyte elution in adsorption chromatography?
How does the elutropic strength of a mobile phase influence analyte elution in adsorption chromatography?
- A lower elutropic strength causes the analyte to elute more rapidly.
- The elutropic strength affects only the resolution, not the elution time.
- Elutropic strength has no impact on analyte elution.
- A higher elutropic strength reduces the analyte's interaction with the stationary phase, promoting faster elution. (correct)
In adsorption chromatography, which factor has the least influence on a chemical's retention?
In adsorption chromatography, which factor has the least influence on a chemical's retention?
Why is alumina preferred over silica as an adsorbent in specific adsorption chromatography applications?
Why is alumina preferred over silica as an adsorbent in specific adsorption chromatography applications?
What principle governs retention in adsorption chromatography?
What principle governs retention in adsorption chromatography?
How do electrostatic interactions, hydrogen bonding and dipole-dipole interactions affect retention?
How do electrostatic interactions, hydrogen bonding and dipole-dipole interactions affect retention?
What is the significance of using Florisil as an alternative to alumina in adsorption chromatography?
What is the significance of using Florisil as an alternative to alumina in adsorption chromatography?
In adsorption chromatography, what characterizes a 'strong' mobile phase relative to the stationary phase?
In adsorption chromatography, what characterizes a 'strong' mobile phase relative to the stationary phase?
What is the critical distinction between liquid-solid chromatography and other forms of liquid chromatography?
What is the critical distinction between liquid-solid chromatography and other forms of liquid chromatography?
Flashcards
Chromatography adsorbents
Chromatography adsorbents
Agents used to provide a stationary phase in a chromatographic process.
Adsorption chromatography
Adsorption chromatography
A type of liquid chromatography where chemicals are separated based on adsorption and desorption on a surface.
High elutropic strength
High elutropic strength
It will bind tightly to the support and cause the analyte to elute more quickly.
Types of adsorbents
Types of adsorbents
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Silica
Silica
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Alumina
Alumina
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Other types of adsorbents
Other types of adsorbents
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Study Notes
- Chromatography adsorbents function as the stationary phase within the chromatographic process.
- These adsorbents activate the mobile phase while selectively absorbing specific chemicals that adhere to the adsorbent's surface
- Additionally, they provide support for the separation of components in plant phytochemicals
- Adsorbents are essential for separating mixture components, particularly in liquid-solid chromatography
- Adsorption chromatography relies on a chemical's retention based on the principles of adsorption and desorption on a surface
Liquid-Solid Chromatography
- Adsorption chromatography can also be referred to as liquid-solid chromatography.
- Retention depends on the analyte's competition with mobile phase molecules for binding to the support surface acting as the stationary phase/adsorbent.
- A chemical's retention in adsorption chromatography depends on its binding strength to the support
- Retention also depends on the surface area of the support
- The retention depends on the amount of mobile phase displaced by the chemical
Factors affecting Retention
- A chemical's retention in adsorption chromatography depends on the binding strength of the mobile phase to the support
- Retention is affected by electrostatic interactions, hydrogen bonding, dipole-dipole interactions, and dispersive interactions such as van der Waals forces
- The mobile phase's binding strength with the support in adsorption chromatography is described by its elutropic strength
Elutropic Strength
- A liquid with high elutropic strength for a support/adsorbent acts as a strong mobile phase because it binds tightly thus causing the analyte to elute faster by spending more time in the mobile phase
- For example, methanol, a polar solvent, has a higher elutropic strength for silica, a polar support, than carbon tetrachloride, a nonpolar solvent.
- Liquids or solutions with low elutropic strength represent a weak mobile phase for the support in adsorption chromatography
Adsorbent Types
- Three main adsorbent types are used in adsorption chromatography: polar acidic, polar basic, and nonpolar adsorbents.
- Silica is the most common polar and acidic support.
- Surface silanol groups on silica adsorb polar compounds and work well for basic substances
- Alumina is the main polar and basic adsorbent
- Like silica, alumina retains polar compounds, but works especially well for polar acidic substances
Adsorbents as Alternatives
- Florisil is an alternative polar and basic adsorbent used instead of alumina, especially when observing catalytic decomposition of an analyte.
- Nonpolar adsorbents like charcoal and polystyrene can be used in adsorption chromatography
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Description
Chromatography adsorbents act as the stationary phase, selectively absorbing chemicals and supporting component separation. In liquid-solid chromatography, retention depends on the competition between the analyte and mobile phase molecules for binding to the support surface. A chemical's retention depends on its binding strength and the surface area of the support.
