Chromatography Techniques (5C) - MCAT Chemical and Physical Foundations of Biological Systems

Time from injection to the analyte peak maximum at the detector. It measures how long an analyte is retained in the column before reaching the detector, reflecting its interaction with the stationary phase.

Higher affinity for the mobile phase elutes first. Greater interaction with the mobile phase allows the component to move faster through the column, resulting in earlier detection.

Less polar compound travels farther (higher $R_f$). In normal-phase setup, less polar solutes have weaker interactions with the polar stationary phase, allowing farther migration with the mobile phase.

A polar solid surface (cellulose paper or silica/alumina on a plate). These materials provide a hydrophilic surface that interacts with polar compounds via adsorption or partitioning.

Two peaks are fully separated with minimal overlap at baseline. It signifies complete distinction between analytes, ensuring accurate quantification without interference.

$\alpha = \frac{k'_2}{k'_1}$ with $k'_2 > k'_1$. It measures the relative retention of two analytes, where a value greater than 1 indicates potential for separation.

$k' = \frac{t_R - t_M}{t_M}$. This ratio quantifies the time an analyte spends retained relative to the unretained time, indicating partition strength.

Analyte with $t_R = 6,\text{min}$ has larger $k'$. Longer retention time yields a higher capacity factor, as $k'$ increases with greater $(t_R - t_M)$.

Relative affinity for stationary phase versus mobile phase. Components with greater affinity for the stationary phase are retained longer, while those preferring the mobile phase elute sooner.

Higher salt (increased ionic strength) elutes bound proteins. Elevated ionic strength competes with bound proteins for resin sites, disrupting electrostatic interactions to release them.

Positively charged analytes (cations) bind most strongly. Cation-exchange resins have negatively charged groups that attract and retain positively charged species more effectively.

Separation by net charge via reversible binding to charged resin. Charged analytes bind electrostatically to oppositely charged sites on the resin, with elution controlled by ionic conditions.

More polar compound elutes first. Polar compounds interact more with the polar mobile phase, leading to weaker retention on the nonpolar stationary phase.

Nonpolar stationary phase with relatively polar mobile phase. This setup reverses the polarity gradient, enabling separation based on hydrophobicity rather than polarity.

More polar mobile phase increases $R_f$ values. Increased polarity enhances solute solubility in the mobile phase, reducing retention on the polar stationary phase.

$R_f = 0.50$. The value is the simple ratio of distances, independent of plate size, for consistent comparison across experiments.

$R_f = \frac{\text{distance traveled by spot}}{\text{distance traveled by solvent front}}$. This ratio quantifies the relative migration of a compound compared to the solvent, reflecting its partitioning behavior.

MS (mass spectrometry). MS provides fragmentation patterns and mass-to-charge ratios, enabling structural identification beyond FID's combustion-based detection.

High volatility and thermal stability are required for GC. Analytes must vaporize without decomposition at column temperatures for effective gas-phase separation.

Separation by size using porous beads that exclude larger molecules. Smaller molecules enter pores and take longer paths, while larger ones are excluded and elute faster.

Larger molecules elute first. They are sterically excluded from pores, traveling a shorter path through the column compared to smaller molecules.

Specific ligand–target binding; elution by competitor or condition change. It exploits highly specific interactions for purification, with elution disrupting the complex without denaturing the target.

GC uses an inert carrier gas; LC uses a liquid solvent. The gaseous mobile phase in GC suits volatile compounds, while liquid in LC allows broader analyte solubility.