Sample: Volatile compounds.

Detectors: Flame Ionization Detector (FID), Thermal Conductivity Detector (TCD), Mass Spectrometry (MS).

Applications: Separation of organic compounds, environmental analysis, forensic science.

Principle: Uses high pressure to force mobile phase through a column packed with small particles.
Types:
- Normal Phase (NP-HPLC): Polar stationary phase, non-polar mobile phase. Separates polar compounds.
- Reversed Phase (RP-HPLC): Non-polar stationary phase, polar mobile phase. Most common type. Separates non-polar/moderately polar compounds.
- Ion-Exchange HPLC: Separates charged species.
- Size Exclusion HPLC: Separates based on size.
Detectors: UV-Vis, Refractive Index (RI), Fluorescence, Mass Spectrometry (MS).
Applications: Pharmaceutical analysis, food analysis, environmental analysis, biochemistry.

Mobile Phase: Liquid solvent (eluent).
Stationary Phase: Thin layer of adsorbent (e.g., silica gel, alumina) coated on a plate.
Procedure: Sample spotted on plate, plate placed in solvent, solvent rises by capillary action.
Visualization: UV light, chemical stains.
Applications: Qualitative analysis, reaction monitoring, purity check, rapid screening.

Mobile Phase: Liquid solvent.
Stationary Phase: Water adsorbed on cellulose paper.
Principle: Partitioning between water and organic solvent.
Applications: Separation of inks, amino acids, sugars. (Less common in modern labs).

Mobile Phase Composition: Affects elution strength, selectivity, and retention times.
Stationary Phase Chemistry: Determines interaction type (polar/non-polar, ion-exchange).
Temperature: Affects viscosity of mobile phase, solubility, and kinetics of interaction.
Column Length/Diameter: Affects plate number and back pressure.
Flow Rate: Affects retention time and efficiency (Van Deemter curve).
Particle Size (LC): Smaller particles lead to higher efficiency but higher back pressure.

$$H = A + \frac{B}{u} + Cu$$

$H$: Plate height (HETP)
$u$: Linear velocity of the mobile phase
$A$: Eddy diffusion term (multiple paths)
$B/u$: Longitudinal diffusion term (diffusion against flow)
$Cu$: Mass transfer term (resistance to mass transfer in stationary and mobile phases)
Optimal Flow Rate: Minimum of the curve, where $H$ is smallest.

Broad Peaks: Overloading, poor column packing, detector issues, extra-column volume.
Tailing Peaks: Secondary interactions with stationary phase, active sites, column voids.
Fronting Peaks: Column overloading, solvent mismatch.
Baseline Noise: Detector instability, mobile phase impurities, temperature fluctuations.
Retention Time Drift: Mobile phase composition changes, column degradati