Plate Theory and Chromatography

These flashcards cover key concepts from plate theory, rate theory, and various methods and detectors used in chromatographic techniques.

Theoretical Plate

A hypothetical discrete section of a column where the analyte reaches equilibrium between stationary and mobile phases.

Plate Number (N)

A measure of column efficiency calculated as $N = 16$ (retention time / peak width) $^2$ or $N = 5.54$ (retention time / peak width) $^{1/2}$.

Rate Theory

A theory that describes how different contributions affect zone broadening in chromatography, represented as $H = A + \frac{B}{u} + Cu$.

Eddy Diffusion (A)

The contribution to zone broadening due to different paths molecules can take through a packed column.

Longitudinal Diffusion (B)

The contribution to zone broadening that results from molecules diffusing from areas of high concentration to low concentration within the column.

Mass Transfer Resistance (C)

The time it takes for an analyte to enter and exit the stationary phase, affected by particle size and stationary phase thickness.

Resolution (R)

A measure of how well two compounds are separated into distinct peaks, calculated as $R_s = \sqrt{N} (\alpha - 1)$.

Split Injection

A method of sample injection where most of the sample is vented, preventing column overload, resulting in sharp peaks but poor sensitivity for trace analysis.

Splitless Injection

A method of sample injection that transfers the entire sample to the column, increasing sensitivity for trace analysis but risking column overload.

Thermal Conductivity Detector (TCD)

A detector that alters the temperature of a heated filament due to changes in thermal conductivity of gas mixtures, yielding a signal proportional to analyte concentration.

Flame Ionization Detector (FID)

A detector that ionizes compounds in a flame and collects ions through a polarized electrode pair, giving a highly sensitive signal that represents analyte concentration.

High Performance Liquid Chromatography (HPLC)

A technique utilizing a reciprocating pump to move solvent and samples through a column for separation.

Suction Stroke (Pump)

The phase where the piston pulls back, increasing the volume of the chamber and drawing fluid into it.

Discharge Stroke (Pump)

The phase where the piston moves forward, decreasing the volume of the chamber and increasing pressure to push fluid out.

Split injection advantages

Sharp peaks, no column overload, accurate

Split injection disadvantages

Poor sensitivity for trace analysis

Splitless injection advantages

Sensitive, all sample goes to column

Splitless injection disadvantages

Risk of column overload, wider peaks, solvent tailing, analyte degration