Analytical Chemistry 2

Q: What is countercurrent extraction?

A:

• A technique for separating solutes,

• based on their differing solubility

• in two immiscible liquids,

• where one phase continuously moves through the other.

Q: How does countercurrent extraction differ from conventional solvent extraction?

A: Countercurrent extraction is

• a continuous process

• that allows for multiple partitioning steps,

• improving efficiency and reducing solvent use,

While conventional methods typically involve batch processes.

Q: What is the primary objective of countercurrent extraction?

A:

• To separate two or more solutes from each other

• through a series of partitions between two liquid phases

• with different distribution coefficients

Q: What are distribution coefficients?

A: Ratios that describe how a solute distributes itself between two immiscible phases, influencing separation during extraction.

Q: Why is continuous extraction advantageous?

A:

• It enhances the mass transfer efficiency of solutes,

• allowing for better separation with less solvent

• compared to batch extraction.

Q: What role does the stationary phase play in chromatography?

A:

• The stationary phase holds one phase in place

• while allowing the mobile phase to move past it,

• facilitating the separation of solutes based on their interactions.

Q: What is meant by "theoretical plates" in chromatography?

A:

Sections in the chromatographic column where:

• Equilibrium is assumed to be achieved.

• Contributes to efficiency and resolution of the separation process.

Q: What is the purpose of a solvent in solvent extraction?

A:

• Transfers solutes from one liquid phase to another:

• Isolating or purifying specific compounds.

Q: How does Gaussian distribution relate to analytical chemistry?

A:

• Describes how solutions distribute around a mean value.

• Essential for understanding the behaviour of solutes during:

• Extraction and chromatography.

Q: What is the significance of solute partitioning in extraction processes?

A: Determines how effectively a solute can be:

• Separated based on its affinity

• for each of the two liquid phases involved in the extraction.

Q: What is the partition coefficient (K)?

A: An equilibrium constant that defines:

• The ratio of a solute's concentration in the two immiscible phases at equilibrium.

• Used to assess extraction efficiency.

Q: What does a higher partition coefficient indicate?

A:

• Suggests that the solute has a greater affinity for the stationary phase compared to the mobile phase.

• Leads to better extraction efficiency from the mobile phase.

Q: What is an immiscible liquid?

A:

• Liquids that do not mix or dissolve in each other, such as oil and water.

• Essential for solvent extraction processes.

Q: What is the meaning of "serial extraction"?

A: A process that involves:

• Multiple stages of extraction.

• Where solutes are extracted successively to improve separation and yield.

Q: How can you calculate the fraction (q) remaining at equilibrium in solvent extraction?

A:

• Using the formula: ​

  

• Where V1 is the volume of the initial phase and V2 is the volume of the other phase.

Q: What are the main components of a chromatography setup?

A:

• A stationary phase.

• A mobile phase (solvent).

• A sample mixture to be separated.

Q: What is the function of the mobile phase in chromatography?

A:

• To carry the sample through the stationary phase, facilitating:

• The separation of components based on their interactions.

Q: How does the concept of equilibrium apply to solvent extraction?

A: Equilibrium is reached when:

• The rate of solute transfer between the two phases is equal.

• Allowing for a stable distribution defined by the partition coefficient.

Q: What types of compounds are commonly separated using solvent extraction?

A:

• Organic compounds, pharmaceuticals, and metal ions.

• Often based on their solubility in different solvents.

Q: What role does temperature play in solvent extraction?

A: Can affect:

• The solubility of solutes in the solvents.

• The partitioning behaviour, influencing extraction efficiency.

Q: What is retention time in chromatography?

A:

• The time it takes for a solute to pass through the chromatographic system and reach the detector.

• Used for identifying and quantifying components.

Q: What is the significance of the mobile phase's polarity in chromatography?

A: The polarity of the mobile phase affects:

• How well different solutes interact with the stationary phase.

• Thus influences their separation.

Q: Why is it important to choose the right solvent in extraction processes?

A: The solvent must:

• Effectively dissolve the target solute.

• Remain immiscible with the other phase to achieve efficient separation.

Q: What is the use of "end-capping" in chromatography?

A: A technique to improve the performance of the stationary phase by:

• Reducing unwanted interactions.

• Enhancing the separation of analytes.

Q: What are some common types of chromatography?

A:

• Gas chromatography (GC)

• Liquid chromatography (LC)

• Thin-layer chromatography (TLC)

• High-performance liquid chromatography (HPLC)

Q: What is the main principle behind gas chromatography?

A:

• Separation of volatile compounds based on:

• Vaporization of the compounds.

• Interaction with a stationary phase.

• Movement with a gas mobile phase.

Q: What is the function of a detector in chromatography?

A:

• Identifies and quantifies separated analytes as they elute from the column.

• Provides real-time data on:

• Concentration of the analytes.

• Retention time of the components.

Q: How is extraction efficiency typically improved in solvent extraction?

A: By optimizing parameters such as:

• Solvent choice.

• Temperature adjustments.

• pH levels.

• Number of extraction stages

  Using techniques like:

• Countercurrent extraction.

Q: What is the significance of baseline resolution in chromatography?

A: Ensures that peaks representing different compounds do not overlap.

Allows for:

• Accurate identification of each component.

• Quantification of each compound without interference.

Q: How does pH influence the distribution coefficient (D) in solvent extraction?

A:

• Alters the ionization state of solutes.

• Affects solubility in the aqueous phase.

• Influences the distribution of solutes between phases.

Q: What is the role of affinity chromatography?

A: Separates biomolecules based on specific interactions such as:

• Antigen-antibody binding.

• Enzyme-substrate interactions.

• Enables targeted purification of specific compounds.

Q: What are some challenges associated with solvent extraction?

A:

• Proper selection of solvents.

• Managing emulsions that may form during extraction.

• Handling toxic or hazardous materials.

• Ensuring complete phase separation.

Q: What does "selectivity" refer to in solvent extraction?

A:

• The ability of a solvent to preferentially extract one solute over others.

• Critical for achieving selective separations in complex mixtures.

Q: What impact does flow rate have on chromatographic separations?

A:

• Affects interaction time of solutes with the stationary phase:

• Too fast: May lead to poor resolution.

• Too slow: Can lead to longer analysis times.

Q: Describe the concept of "sample matrix" in chromatography.

A:

• The composition of the sample being analyzed.

• Can influence the separation process.

• May require method adaptations to mitigate matrix interference.

Q: What is the purpose of a mobile phase modifier in liquid chromatography?

A: Improves separation efficiency by altering:

• Polarity of the mobile phase.

• Viscosity of the mobile phase.

• pH of the mobile phase.

• Enhances interactions with the stationary phase.

Q: How does the choice of stationary phase affect the outcome of chromatography?

A:

• Different stationary phases provide varying polarities and functionalities.

• Can be tailored to enhance separation of specific analytes based on their properties.

Q: What is the importance of calibration in chromatography?

A:

• Establishes response factors for analytes.

• Ensures accurate quantification through comparison against known standards.

Q: How does adsorption chromatography differ from partition chromatography?

A:

Adsorption chromatography:

• Separates analytes based on their ability to adhere to the stationary phase.

Partition chromatography:

• Relies on differential solubility in liquid phases.

Q: What are some common applications of solvent extraction ?

A:

• Recovery of essential oils.

• Separation of metals.

• Extraction of pharmaceuticals.

• Purification of environmental samples.