Q: Which equation correctly defines the partition coefficient $$P$$ for a solute $$A$$ between two immiscible solvents $$S_1$$ and $$S_2$$?

$$P = \frac{\text{Concentration of A in } S_2}{\text{Concentration of A in } S_1}$$

Question 1

Which of the following best describes the main advantage of using supercritical fluid extraction (SFE) over traditional liquid-liquid extraction methods?

Accepted Answer

SFE allows for faster mass transfer rates and tunable solvent power by adjusting pressure.

Question 2

A pharmaceutical chemist needs to extract a weak organic base from a cream formulation. Which sequence of steps would maximize the extraction efficiency?

Accepted Answer

Dissolve the sample in water, acidify with HCl, extract with a non-polar organic solvent, then make alkaline and extract with a polar organic solvent.

Question 3

Which equation correctly defines the partition coefficient $$P$$ for a solute $$A$$ between two immiscible solvents $$S_1$$ and $$S_2$$?

Accepted Answer

$$P = \frac{	ext{Concentration of A in } S_2}{	ext{Concentration of A in } S_1}$$

Question 4

Which of the following is a key advantage of solid phase extraction (SPE) compared to liquid-liquid extraction?

Accepted Answer

SPE can be automated and allows for sample concentration before analysis.

Question 5

A sample contains both a weak organic acid and a weak organic base. Which extraction strategy would best separate these two analytes?

Accepted Answer

Adjust pH to selectively ionize one analyte, extract the unionized form into an organic solvent, then adjust pH and repeat for the other analyte.

Question 6

Which of the following stationary phases would be most suitable for extracting polar compounds not well retained by lipophilic adsorbents in SPE?

Accepted Answer

Polar surface-modified silica gels

Question 7

Why is the use of internal standards advisable in solid phase extraction (SPE) procedures?

Accepted Answer

To correct for variations in extraction efficiency and sample loss.

Question 8

Which of the following best explains why supercritical CO$$_2 is $$commonly used as a solvent in SFE?

Accepted Answer

It has a low critical temperature and is non-toxic and non-flammable.

Question 9

Which of the following is a limitation of traditional liquid-liquid extraction techniques?

Accepted Answer

Limited selectivity and possible emulsion formation.

Question 10

A pharmaceutical company needs to extract corticosteroids from an oily cream. Which solvent system would be most appropriate based on the study materials?

Accepted Answer

Disperse the sample in warm hexane, then extract with an equal volume of ethanol.

Question 11

Which type of SPE adsorbent would be most suitable for selectively extracting catechols and glycosides?

Accepted Answer

Borate gels

Question 12

What is the main function of the washing step in solid phase extraction (SPE)?

Accepted Answer

To remove contaminants and interferents while retaining the analyte on the adsorbent.

Question 13

Which of the following best describes the principle behind molecularly imprinted polymers (MIPs) used in SPE?

Accepted Answer

They are organic polymers with cavities shaped for specific target molecules.

Question 14

Which of the following is NOT a typical step in the solid phase extraction (SPE) process?

Accepted Answer

Formation of emulsions

Question 15

Why are silica gel-based SPE adsorbents not suitable for use with strong alkali or acid?

Accepted Answer

They are unstable and degrade under strong alkali or acid conditions.

Question 16

Which of the following best describes the role of a Soxhlet extractor in solid-liquid extraction?

Accepted Answer

It allows for continuous extraction of analytes from a solid sample using a boiling solvent.

Question 17

Which of the following is a real-world application of immunoaffinity gels in SPE?

Accepted Answer

Selective extraction of analytes using antibodies attached to the adsorbent surface.

Question 18

A sample contains a mixture of neutral, acidic, and basic excipients. Which extraction method would best separate these components for analysis?

Accepted Answer

Sequential pH adjustment and extraction with solvents of varying polarity.

Question 19

Which of the following is a limitation of using molecularly imprinted polymers (MIPs) in SPE?

Accepted Answer

They are only selective for a narrow range of analytes.

Extraction Techniques in Analytical Chemistry: Solid-Liquid, Liquid-Liquid, and Solid Phase Extraction

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