Chromatography Glossary


Ejector Stage

A term used in Mass Spectrometry for the portion of a diffusion pump where molecules pass through and are directed to the inlet of the roughing pump.

Electrochemical Detector

Electrochemical Detectors can be classified into the following types: Amperometric, conductimetric and potentiometric.

1. Amperometric Detector: Based on the measurement of current resulting from oxidation or reduction of analyte molecules at the surface of an electrode in a flowthrough cell. During an oxidation reaction, electrons are transferred from the analyte to the electrode. The reverse occurs in reduction reactions.

2. Conductivity Detector: Based on the measurement of the electrical conductivity of analytes as they move in an electric field between electrodes in a flow through cell.

3. Potentiometric Detection: Based on the measurement of the potential that develops at an electrode or across a membrane, such as in an ion-specific or pH electrode.


Electrochromatography is a hybrid technique combining capillary zone electrophoresis (CZE) and HPLC. The technique is like CZE but utilizes packed fused silica capillary columns (packed with modified silica particles), so that both partitioning and electrophoretic mobility affect the separation. Using electricallydriven flow, significantly higher efficiencies can be obtained than with pumped (laminar) flow. Capillary Electrochromatography is abbreviated "CEC".

Electron Beam

In Mass Spectrometry, a beam of electrons created in the ion source by emission of electrons from the filament and the focusing effect of the magnet. The electron beam is within the ionization chamber and provides constant opportunity for collisions to occur between electrons and sample molecules.

Electron Energy

A term used in Mass Spectrometry for energy gained by an electron as it moves form the ion source filament to the ion volume. Electron energy is typically measured in electron volts, eV. For an EI source, electron energy is typically 70 eV.

Electron Focus

A term used in Mass Spectrometry for part of the ion source positioned near the filament. The electron focus has a negative voltage, which repels electrons across the ionization chamber.

Electron Ionization

In Mass Spectrometry, the collision between electrons and sample molecules resulting in the formation of an ion is referred to as ionization. This process, which breaks sample molecules into a characteristic collection of fragments, occurs in the ionization chamber. EI spectra are the most common type of spectra in commercial spectral databases.

Electron Multiplier

A common type of mass spectrometer detector. The electron multiplier converts the ion current into an electrical current.


A technique for the separation of ions by rate and direction of migration in an electric field.


Evaporative Light Scattering Detector. Also known as the Mass Detector. It works by detecting light scattered off particles remaining after the nebulized eluent is evaporated.


The elution solvent plus any analytes and interference which are eluted from the column. The eluent after it passes through the column.


Eluent refers to the mobile phase - the solvent mixture used to perform a separation.

Eluent Sensitivity

Refers to detectors which respond to small changes in eluent flow, eg. refractive index, amperometric, conductivity and infrared.

Eluotropic Series

Arrangement of common solvents in order of increasing strength for the elution of analytes from a particular sorbent. The eluotropic strength of a solvent is represented by e0.


The desorption of the target analyte from the sorbent which can be brought about by changing the solvent composition in order to disrupt the interactions between the solutes and the stationary phase.

Elution Volume

The volume of solvent used to elute the analyte or the volume of elution solvent required to elute the analyte with quantitative (~100%) recovery.


This is the name of the technique used to divide packing particles by size. It is most often used to separate ion exchange resins,eg amino acid resins, which require a very narrow size range. Water flows upwards into a tube. The unsized beads are added to the water and find their own level according to their density and particle size. The various sizes of particles can then be removed from the water at certain levels.

Emission Wavelength

In fluorescence detection, the wavelength used for the measurement of fluorescence intensity, ie., the wavelength at which the sample re-emits the incident light. Fluorescence detectors generally measure the emission at 90° to the incident radiation. This minimizes background radiation from the excitation beam, and enhances linearity and sensitivity. Chemiluminescent detectors also measure light emission, but the signal is generated from the sample itself due to some light-emitting chemical reaction, eg., peroxyoxylate chemiluminescences catalyzed by hydrogen peroxide.


A suspension of globules or micelles of one liquid in a second liquid, which will not mix.


Two stereoisomers whose molecules are non-superimposable mirror images of one another. They have identical chemical and physical properties and contain the same internal energy. Only when enantiomers are placed in a chiral environment (in a chiral column or in any living system) do they show different properties and energies and should be thought of as two completely different compounds. In the human body, enantiomers often have different physiochemical properties, with different pharmacodynamics and kinetics.


In LC chromatography the reaction of a silylating agent with unreacted accessible silanols remaining on the silica gel surface after the initial bonding reaction.


This is the fitting at the end of a column that connects it to the injector or detector.

Entrance Lens

In Mass Spectrometry, one of the lenses of an ion source that is positioned at the front of the quadrupole. The entrance lens has a voltage applied to it to help focus and accelerate ions into the quadrupole.


Pumping mobile phase through the column until the detector signal baseline stabilizes is referred to as equilibration. A flat, stable baseline is desired before sample is injected. Column equilibration is required when mobile phase conditions are changed. The equilibration process is usually accomplished by pumping about 20 to 30 column volumes of mobile phase through the column.


Abbreviation of Ethyl Acetate. MW 88.11, Boiling Point 77 C, Polarity Index 4.4, Solubility in water 8.7% at 20C, UV cutoff 256nm. Common solvent used in normal phase chromatography.

Exchange Capacity

The concentration of fixed ionic sites on an ion exchange packing, usually expressed in milliequivalents per gram. Can also be called Ion exchange capacity.

Excitation Wavelength

In fluorescence detection, the wavelength used to illuminate (excite) the sample in order to make it fluoresce, ie., the wavelength of the incident beam.

Exclusion Limit

In SEC the exclusion limit is the upper limit of molecular weight, above which molecules will elute at the same retention volume.

Exclusion Volume

The exclusion volume on SEC packing material refers to the retention volume of a molecule. All molecules larger than the size of the largest pore will be totally excluded and elute at the interstitial volume of the column. The pore size of the polymer gel is controlled by adjusting the amount of crosslinking agent.

External Standard

A method relating detector response to sample concentration in order to perform quantitative analysis. Standard solutions (ie., dilutions) of a sample to be quantitated are prepared and equal volumes chromatographed. Peak heights or areas are plotted versus concentrations to produce a calibration curve. Detector response of an actual sample is then interpolated off the calibration curve to determine concentration.

Extra-Column Effects

Refers to the bandspreading effects of parts of the chromatography system outside the column. These effects must be kept to a minimum, in order to maintain the efficiency of the column. System components which contribute to bandspreading are the injector, endfittings, connecting tubing, frits, detector cell volume and internal detector tubing. All contributions are additive.

Extra-Column Volume

IUPAC Definition: The volume between the effective injection point and the effective detection point, excluding the part of the column containing the stationary phase. It is composed of the volumes of the injector, connecting lines and detector.


The transfer of the analyte from one phase to another. Includes solid phase extraction (SPE), liquid liquid extraction (LLE), and other sample preparation related techniques.


In Mass Spectrometry, stands for Fast atom bombardment. This is a device placed in the ion source that focuses ions and atoms through a gun onto a liquid surface containing the dissolved sample. This process ejects secondary ions from the liquid surface that are detected by the mass spectrometer.


Abbreviation for fatty acid methyl ester.

Fast LC

This term refers to the use of short columns, usually 3 to 7 cm in length, with conventional internal diameters, 2 to 6 mm. These are then packed with small particles of 3 to 5um/dp. Separation times of minutes and sometimes even seconds have been known.

Feedback Control

An electronic control mechanism that reads pressure or motor torque and returns a signal to control the speed of the pump motor. Used for reducing pump pulsations, compensating for compressability factors, and for improving flow accuracy and stability.


The part of a chromatographic system union that deforms around the tubing to create a leakproof seal.


In Mass Spectrometry, a heated wire in the ion source which produces electrons. A filament is required for ionization to occur in EI and CI ion sources.

Filter Parameter

User-selectable integrator or data system parameter which controls the amount of noise filtering applied to the signal before the peak detection algorithms are applied.


Sorbent particles that are left over from the manufacturing process that are considerably smaller than the average finished-product particle.


A fitting that can be tightened to working pressures without the use of a wrench, or spanner.


The tubing and fittings which make the connections from one component of the HPLC to the others must be minimized with respect to dead volume, mixing and band broadening. Column hardware endfittings today are almost all the female inverted (internal) type and utilize 10-32 type fittings to attach 1/16" tubing of any kind (PEEK, stainless steel or titanium). 1/4"-28 type fittings are also commonly used in HPLC for other system components. A nut and ferrule (sometimes it is one piece, as with fingertight fittings) is used to swage or tighten the tubing onto the fitting. You can use ferrules interchangeably, but once the ferrule is swaged in a particular type of fitting, it should be used with that type of fitting only.