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What does chromatographic peaks represent?  

• It represents the volume of the mobile phase required to elute a compound from an LC column. 

• It represents the visual representation of separated compounds and the result of the separation process.

• It represents the associated time for a specific analyte to travel through the chromatography system.

• It represents the measure of how well two compounds are separated from each other during the chromatographic process.

Answer explanation

Each chromatographic peak represents the compound that was detected by the chromatography system. The measure of how well two compound are separated is called the resolution peak.

Which of the following best describes the resolution of the peak?

• The peaks indicate a good resolution due to column efficiency.

• The peaks present a low resolution due to overlapping of peaks.

• The peaks indicate a good resolution due to column selectivity

• The peaks present a low resolution due to narrow and sharp peaks.

Answer explanation

A peak that produces narrow and sharp peaks indicates a good resolution due to column efficiency. Column selectivity explains that if the peaks are not overlapping with each other, it presents a good resolution.

Size-exclusion chromatography is a technique that separates molecules based on their size using porous beads in a column. Which of the following food components would elute faster?

• Gliadin

• Casein

• Starch

• Glutenin

Answer explanation

Glutenin is a large protein, much larger in molecular weight compared to gliadin, casein, or starch. Due to its size, glutenin cannot fit into the pores of the stationary phase and bypasses them entirely, moving through the column more quickly.

Which chromatography technique is best suited for extracting essential oils?

• Supercritical Fluid Chromatography

• Gas Chromatography

• Liquid Chromatography

• Column Chromatography

Answer explanation

Essential oils are primarily composed of volatile, nonpolar compounds such as terpenes and terpenoids, making SFC an ideal technique for their extraction and analysis.

In Gas-Liquid (G-L) Chromatography, which gas is usually used as the mobile phase?

• Helium

• Oxygen

• Butane

• Ethanol

Answer explanation

In gas chromatography, the mobile phase is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen. 

In affinity chromatography, what do you call the special linker attached to the stationary phase that binds to the target molecule during the process?

• Ligand

• Silica gel

• Porous beads

• Binding agent

Answer explanation

A ligand, chosen based on its specificity/selectivity and strength of interaction with the analyte, is immobilized on a suitable support material (stationary phase).

What is the primary principle behind chromatography as a separation technique?

• Molecules are separated based on their charge properties in the stationary phase.

• Molecules interact differently with the stationary and mobile phases, leading to separation.

• Separation is achieved solely by the molecular weight of the compounds.

• The Stationary phase moves all molecules from the mobile phase.

Answer explanation

The stationary phase and the mobile phase interact differently with the molecules being separated. This differential interaction causes the molecules to move at different rates through the stationary phase, leading to their separation based on factors such as polarity, size, charge, or other chemical properties.

Which of the following best describes the stationary phase in chromatography?

• It can be a liquid or gas that continuously moves along with the mobile phase.

• A phase that flows rapidly, carrying the components of a mixture with it.

• A solid or liquid layer that interacts with the mobile phase to achieve separation.

• A gas or liquid layer that interacts with the mobile phase to achieve separation.

Answer explanation

The stationary phase is always composed of a solid phase or a layer of a liquid adsorbed on the surface of a solid support. The mobile phase, on the other hand, is always composed of liquid, gas components, or supercritical fluid, depending on the type of chromatography. 

Which of the following is NOT a limitation of technique-specific challenges of chromatography?

• Gas chromatography can only analyze volatile and thermally stable compounds.

• Matrix effects occur when other components in the sample interfere with the analyte’s signal, leading to poor detection or inaccurate results.

• HPLC can be costly and poses environmental concerns.

• TLC has lower resolution and reproducibility making it less reliable for precise quantitative work.

Answer explanation

Technique-specific challenges in chromatography primarily arise from the need to carefully manage sample preparation, select the appropriate stationary phase and mobile phase for optimal separation, potential interferences from matrix components, and ensuring accurate detection of analytes, which can vary depending on the specific chromatography method like HPLC, GC, or TLC, often requiring specialized techniques to address these issues depending on the sample type and desired analysis level.

Which of the following is a limitation of scalability issues of chromatography?

• Preparing large quantities requires bigger columns and more solvents, which increases costs exponentially.

• Overlapping peaks are a common problem, making it difficult to identify individual analytes.

• Baseline instability and noise can further complicate interpretation, especially in low-concentration samples.

• Preparing samples often requires multiple steps, including extraction, filtration, and concentration, which can be time-consuming and prone to contamination.

Answer explanation

Scaling up to larger column volumes can drastically increase the cost of the stationary phase, especially when using specialized resins or particles required for specific separations.