Gas Chromatography Fundamentals and Instrumentation

Vocabulary practice flashcards covering essential concepts, instrumental components, injection modes, column mechanics, and mathematical terms in gas chromatography.

Gas Chromatography

A separation process where compounds in a mixture are separated by their affinity for a stationary phase and relative volatility while being moved by a mobile gas phase through a column.

Carrier Gas

The mobile phase in gas chromatography (such as hydrogen or helium) that moves analytes through the column.

Makeup Gas

An auxiliary gas (commonly nitrogen) that sweeps the detector to prevent separated compounds from rejoining or broadening.

Inlet Septum

A rubber barrier pierced by the injection syringe that reflexes to close the inlet to the atmosphere, preventing carrier gas and pressure loss.

Liner

A chamber made of deactivated glass, sometimes packed with glass wool, that assists in vaporizing the sample and protects it from the metal inlet.

Split Injection

An injection mode for higher concentration samples where a high flow rate enters the inlet, splitting the sample and carrier gas between the column and the vent.

Splitless Injection

An injection mode for low limits of detection where most of the sample enters the column while the split vent remains closed for a set period before purging.

On-Column Injection

An injection technique for thermally labile compounds where the sample is injected directly onto the column, bypassing the heated injection port.

Direct Injection

An injection method used for trace compound levels where the column is directly sealed to the liner, avoiding contact with inlet seals or glass wool to prevent adsorption or degradation.

Purge and Trap Injection

A headspace technique where volatile organic compounds (VOCs) are purged from a matrix by an inert gas, captured in an adsorbent trap, concentrated, and injected onto the column.

Programmable Temperature Vaporization (PTV)

An injection technique where the sample is introduced into a cold inlet and then heated via a temperature program to vaporize solvents separately from compounds of interest.

Temperature Programming

An oven mode utilizing a temperature ramp over time to enhance separation based on compound structure and chemistry.

Isothermal Mode

An oven operating mode where the oven maintains a constant temperature throughout the entire analysis cycle.

Ionic Bonding

Electrostatic forces between ions resulting in a complete transfer of electrons between two atoms.

Covalent Bonding

A chemical bond formed when two atoms share electrons to become more stable.

Ion-Dipole Interaction

An intermolecular force resulting from the electrostatic interaction between an ion and a polar molecule.

Dipole-Dipole Interaction

An intermolecular interaction occurring between polar molecules containing permanent charge separations.

Hydrogen Bonding

A specific type of dipole-dipole interaction occurring when a hydrogen ($H$) atom is covalently bonded to highly electronegative atoms such as nitrogen ($N$), fluorine ($F$), or oxygen ($O$).

Dipole-Induced-Dipole Interaction

An interaction occurring when a nonpolar molecule is exposed to the force field of a permanent dipole, momentarily repelling electrons and creating an uneven charge distribution.

London Dispersion Forces

Temporary intermolecular forces caused by instantaneous, temporary polarization of nonpolar molecules creating a chain reaction of induced dipoles.

Van der Waals Forces

A collective term for weak intermolecular forces, including hydrogen bonding and London dispersion forces.

Column Bleed

The degradation of the column's stationary phase over time or due to exposure to damaging sample components or oxygen.

Capillary Column

A hollow, narrow tube coated with a liquid phase or adsorbent on its inner surface, protected externally by a polyimide resin coating over fused silica.

Capillary Column Types (WCOT, SCOT, PLOT)

The three broad classifications of capillary columns: Wall-Coated Open Tubular (WCOT), Support-Coated Open Tubular (SCOT), and Porous-Layer Open Tubular (PLOT).

Eddy Diffusion

The $A$ term coefficient in the Van Deemter equation that accounts for mobile phase turbulence and peak broadening caused by multiple flow paths (eddies) in a column.

Longitudinal Diffusion

The $B$ term coefficient in the Van Deemter equation accounting for peak broadening due to diffusion within the mobile phase or carrier gas.

Mass Transfer Resistance

The $C$ term coefficient in the Van Deemter equation representing interactions and movement of compounds in and out of the mobile and stationary phases.

Flow Rate

The volume of mobile phase passing through the column over a given period of time.

Linear Velocity

The rate of speed ($\mu$) at which the mobile phase moves through the chromatographic column.

Height Equivalent to a Theoretical Plate (HETP)

A measure of column efficiency defined as column length ($L$) divided by the number of theoretical plates ($N$), expressed as $HETP = \frac{L}{N}$.

Column Efficiency ($N$)

A dimensionless measure of column performance relating the retention time ($t_R$) of an analyte to peak broadening.

Partition Coefficient

A measure of an analyte's tendency to dissolve in or distribute between two immiscible phases (stationary phase and mobile phase).

Distribution Coefficient

A pH-dependent equilibrium metric demonstrating the ratio of compound concentrations across two phases.

Retention Time ($t_R$)

The time elapsed between sample injection and the arrival of an analyte peak at the detector.

Mobile Phase Hold Time ($t_M$)

The time required for the mobile phase or an unretained compound to travel through the column without interacting with the stationary phase.

Selectivity ($\alpha$)

The ratio of the adjusted retention times or capacity factors of two analytes, describing their relative interaction with the stationary phase.

Retention Factor ($k_A$)

A parameter describing the migration rate of an analyte on a column, defined as $k_A = \frac{t_R - t_M}{t_M}$.