Glossary of Common Chromatography Terms

A

active site
The site of a protein that binds with ligands during a reaction.

affinity binding column
Affinity binding columns separate based on the strength of the bonding between analyte molecules and specific ligands attached to the surface of the stationary phase.

allosteric site
A site on a protein which can influence the active site of a protein by binding another ligand.

analyte
A substance to be analyzed, identified, or measured. Usually part of a sample mixture.

antibody
A blood protein produced during an immune response. Antibodies are produced with a strong affinity to biomolecules the body considers foreign, called antigens.

antigen
A toxin or foreign substance that induces an immune response in the body. Antigens are strong ligands to immunogenic biomolecules called antibodies.

aromatic compounds
Aromatic compounds are compounds that contain conjugated planar ring systems of delocalized pi (π) electron clouds.

B

buffer
A solution that consists of a mixture of a weak acid and its conjugate base. Helps to maintain a pH level within a solution while reactions occur.

C

capillary action
The ability of a liquid to flow in narrow spaces without the assistance of gravity.

carrier gas
The gaseous mobile phase used in gas chromatography.

cationic exchange
A form of ion-exchange chromatography that uses resins or packings that separate cations.

chromatography
The separation of a mixture by passing it through a medium in which its components move at different rates.

column
Diba Omnifit EZ Chromatography Columns with Adjustable Endpieces The component of the chromatography system where the separation of the sample occurs. Can be an actual column or a loop of tubing.

column packing
The solid material, usually a porous solid with or without a chemically interactive surface placed inside or on the walls of a column, used to differentially retain analytes; also referred to as the stationary phase.

D

desalting
Technique where low-molecular weight salts and other compounds can be removed from nonionic and high-molecular weight compounds.

diffusion
The net movement of molecules or atoms from a region of high concentration to a region of low concentration because of random motion of the molecules or atoms.

dipole A molecule in which a concentration of positive electric charge is separated from a concentration of negative charge.

E

eluate
The combination of mobile phase and solute exiting the column; also called effluent.

eluent
The mobile phase used to carry out a separation.

enantiomer
Each of a pair of molecules that are mirror images of each other.

F

frit
A porous disc used as a barrier to prevent the onward movement of particulate matter.

G

gas chromatography (GC)
Gas chromatography is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition.

gas generation
Parker Balston's Hydrogen Generators for Fuel Gas The creation of carrier gas from atmospheric components for use in gas chromatography.

guard column
A small column placed between the injector and the analytical column to protect the analytical column against contamination by sample particulates and strongly retained species.

H

high-performance liquid chromatography (HPLC)
A chromatographic technique used to separate, identify and quantify sample components in a liquid mixture, often characterized by high pressure.

his-tagging
The addition of a multi-histidine tag to a protein, aids in selection during immobilized metal affinity chromatography (IMAC) assays.

hydrogen bond
An electrostatic attraction between a hydrogen item and other electronegative items such as oxygen and nitrogen.

hydrophilic
A chemical that mixes with or can be dissolved in water.

hydrophilic interaction chromatography (HILIC)
HILIC is a variant of HPLC where a partition of aqueous solution is created within the column to separate analytes based on their polarity and hydrophilic nature.

hydrophobic
A chemical that repels or fails to mix with water.

I

ion
An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

ion-exchange chromatography (IEC)
The process in which ionized solutes can be separated from non-unionized or partially ionized solutes using ions.

ion pair chromatography (IPC)
A form of chromatography in which ions in solution can be paired or neutralized and separated as an ion pair on a reversed phase column.

isomer
Each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties.

K

k-factor
The ratio of time an analyte is retained in the stationary phase to the time it is retained in the mobile phase.

L

ligand
An ion or molecule that binds to another (usually larger) molecule.

limit of detection
The lowest quantity of a substance that can be distinguished from the absence of that substance.

limit of quantitation
The lowest concentration of an analyte that can not only be reliably detected but at which some predefined goals for bias and imprecision are met.

liquid chromatography
A chromatographic technique in which liquid acts as the mobile phase.

low-pressure liquid chromatography (LPLC)
A chromatographic method where a solvent containing sample is passed over a prepared separation column under the force of gravity or flow rate provided by a low-pressure pump.

M

mass spectroscopy
An analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratios.

mobile phase
The part of a chromatographic system that carries the analyte through the system and stationary phase.

molecular weight
The mass of a molecule, calculated as the sum of the atomic weight of the atoms contained in it.

N

nonpolar
A molecule where electrons are distributed symmetrically and thus do not have an abundance of charge at the opposite sides.

normal phase chromatography
A chromatographic method in which the mobile phase is less polar than the stationary phase. In this environment, polar molecules are retained longer than non-polar molecules.

P

partitioning
The distribution of a solute between two immiscible solvents (such as aqueous and organic phases).

peak
The profile of an analyte compound as it is eluted from a column through a detector; usually depicted on a visual output as a spike in the baseline.

peristaltic pump
Ismatec Reglo Independent Channel Control (ICC) Peristaltic Pumps A pump which works by compressing flexible tubing between two rotors to create a vacuum and pull liquid from a source and then push that liquid out through the rest of the fluid pathway.

piston pump
The standard style of pump used in most automated liquid chromatographic systems, where small, inert pistons aspirate and dispense reagent(s) in timed sequence to create a continuous and nearly pulse-free flow of the mobile phase through the system.

polar
A molecule where electrons are distributed asymmetrically and thus have a charge at the opposite sides of the molecules.

R

retention time
The time between injection and the appearance of the analyte at the end of the column. It is usually measured from the time of the injection of the sample to the time of the maximum detector response to the presence of the analyte.

reversed phase chromatography
A chromatographic method in which the mobile phase is more polar than the stationary phase. In this environment, non-polar molecules are retained longer than polar molecules.

S

sample
A mixture containing two or more molecular species that needs to be separated for analysis.

selectivity
The fundamental ability of a stationary phase to selectively retain substances based on their chemical characteristics.

sensitivity
Degree of detector response to a specified solute amount per unit time or per unit volume often defined by lower limit of detection.

solvent
Cole-Parmer Methanol
A chemical medium able to dissolve other chemicals within itself; acts as a mobile phase during low-pressure liquid chromatography and high-performance liquid chromatography.

T

tailing
Phenomena wherein a normal Gaussian peak is followed by an asymmetrical factor greater than one. The peak will have an extended trailing edge.

thin-layer chromatography (TLC)
A chromatographic technique used to separate nonvolatile mixtures wherein a thin layer adsorbs onto a stationary phase plate. The compounds within the mixture travel varying distances across the plate, creating a visual separation.

XYZ

zwitterion
Molecule with two or more functional groups with one negative and one positive charge resulting in a neutral net charge. Also called a dipolar ion.

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