Chromatography techniques Knowledge-Based Practice

Questions

1. 1.

   In gas chromatography (GC) using a nonpolar capillary stationary phase, which statement correctly describes the primary factor governing analyte retention and the role of the mobile phase?

   • A) Retention is primarily determined by chemical solvation gradients created by the reactive carrier gas, which selectively binds polar functional groups.
   • B) Retention is primarily governed by analyte boiling point and vapor pressure, while the inert carrier gas acts solely as a physical transport medium.
   • C) Retention depends mainly on differential size exclusion within the open tubular column, causing larger molecules to elute first.
   • D) Retention is controlled entirely by ionic exchange interactions occurring between the gaseous ions and the immobilized liquid phase.
2. 2.

   In affinity chromatography, which statement correctly describes the primary mechanism of analyte retention and the typical strategy used for elution?

   • A) Retention relies on differential penetration into porous gel beads according to hydrodynamic radius, and elution is achieved by progressively increasing the mobile phase flow rate.
   • B) Retention is driven by hydrophobic interactions with an immobilized nonpolar alkyl chain, and elution is achieved by steadily increasing the organic solvent concentration.
   • C) Retention is based on specific, reversible biological interactions between the analyte and an immobilized ligand, and elution is typically achieved by adding a competitive soluble ligand or altering buffer pH.
   • D) Retention depends entirely on non-specific electrostatic attractions to charged sulfonate groups, and elution is achieved by lowering the ionic strength of the buffer solution.
3. 3.

   In cation-exchange chromatography, which statement correctly describes the nature of the stationary phase and the typical conditions required to elute retained analytes?

   • A) Positively charged analytes bind to a positively charged stationary phase and are eluted by lowering the mobile phase ionic strength.
   • B) Negatively charged analytes bind to a sulfonated stationary phase and are eluted by decreasing the mobile phase salt concentration.
   • C) Positively charged analytes bind to a negatively charged stationary phase and are eluted by increasing the mobile phase salt concentration or increasing the pH.
   • D) Neutral analytes bind preferentially via hydrophobic forces and are eluted by introducing a nonpolar organic modifier to the mobile phase.
4. 4.

   In size-exclusion chromatography (SEC), which statement correctly describes the mechanism of separation and the resulting elution order of molecules?

   • A) Smaller molecules elute first because their higher diffusion rates allow them to travel more rapidly through the mobile phase.
   • B) Larger molecules elute first because they are excluded from the internal pores of the stationary phase and travel only through the interstitial volume.
   • C) Molecules with greater net positive charge elute first because they are repelled by the neutral porous beads of the stationary phase.
   • D) Hydrophobic molecules elute first because they are displaced more rapidly by the aqueous mobile phase from the matrix surface.
5. 5.

   In reversed-phase high-performance liquid chromatography (RP-HPLC), which statement correctly describes the relative polarities of the phases and the elution order of analytes?

   • A) A nonpolar stationary phase is paired with a polar mobile phase, causing the most polar analyte to elute first.
   • B) A polar stationary phase is paired with a nonpolar mobile phase, causing the most polar analyte to elute first.
   • C) A nonpolar stationary phase is paired with a polar mobile phase, causing the least polar analyte to elute first.
   • D) A polar stationary phase is paired with a nonpolar mobile phase, causing the least polar analyte to elute first.

Answers and step-by-step solutions appear after you finish the test.