Chromatography Glossary



Dalton is the unit used to express molecular weight.

Data Collection Rate

The frequency at which an integrator or data system measures the signal from the detector.

Daughter Ion

In Mass Spectrometry, an ion formed as a result of fragmentation of another ion. Also known as "product ion".


An abbreviation used in Mass Spectrometry for Desorption Chemical Ionization, which is ionization by a reagent gas of material introduced to the ion source on a specially designed probe. The probe is capable of high heating rates and this causes rapid desorption of the material with relatively little decomposition.


Abbreviation of Dichloromethane, more commonly referred to as Methylene Chloride. MW 84.93, Boiling Point 39.75 C, Polarity Index 3.1, Solubility in water 0.24% at 20 C, UV cutoff 235nm. Common solvent used in normal and reversed phase chromatography and in gel permeation chromatography (GPC).


Hydrogen bonding of water to surface hydroxyl groups on underivatized oxides (i.e., silica or alumina). When water is present in the mobile phase, it bonds to these groups and makes them inaccessible to solute adsorption. The process decreases the overall retention. Removal of the adsorbed water reactivates the support.

Dead Volume

Also known as Extra-Column Dead Volume (ECDV). The internal volume of the chromatographic components between the injector and the detector exclusive of the column. The sum of : Inter-particle volume (space between particles) + Intra-particle volume (space due to porosity of particles) + Extra-column volume (injector, detector, tubing and fittings). This volume can be determined by injecting a non-retained compound. The volume is calculated from its retention time multiplied by the flow rate.


Diethylaminoethyl. A common ion-exchange functional group for weak anion exchange (under conditions where the DEAE group is protonated).


In Mass Spectrometry, part of an electron multiplier detector which has a negative voltage applied to adjust the trajectory of ions as they enter the horn. Also known as X-ray lens.


The process of removing dissolved gases from an eluent. Usually accomplished by sparging with helium, although use of electrically driven vacuum degassers is now more effective. Boiling and utrasonics are less effective alternatives.

Degassing (Mass Spec.)

In MS systems, the removal of gases from a vacuum system by external conditions. For example, an ion gauge is degassed by an internal heater.


Loss or reduction of quality, integrity, or character; a chemical reaction that breaks down a molecule into smaller parts.


A process pertaining to a change in the structure of a protein from a regular (normal) to an irregular (often rigid, rod-like) arrangement of the polypeptide chain under certain chemcial conditions. Denaturation destroys the tertiary and quaternary structure of a protein. Mobile phases containing high concentrations of organic modifiers will produce such effects, which can often improve chromatography of these types of molecules.


A chemical reaction which appends a functional group or compound to the components of interest. Derivatization is usually carried out to provide selectivity or reduce interferents and/or improve detection sensitivity. Derivatization can take place pre- or post column.


Is a technique for removing low molecular weight salts and other compounds from non-ionic and high molecular weight compounds. Use of an SEC column to exclude large molecules and retain lower molecular weight salts is an example.


The transfer of the solute from the adsorbent into the mobile phase.


An instrument which responds to analyte component concentrations, and can be calibrated to give a quantitative determination of analyte concentration.

Detector (Mass Spec.)

The part of the mass spectrometer where the mass-selected ions are collected and counted. An electron multiplier detector is commonly used in a mass spectrometer.


A synthetic or natural chemical that reacts with the surface of a molecule to make it more soluble in a given liquid. Sometimes referred to as surfactants. Detergents are sometimes used in biochromatography to disperse protein aggregates and/or denature proteins, or in micellar chromatography for the direct injection of eg., urine and serum. Detergents have polar "head" groups that can be anionic, cationic, zwitterionic or non-ionic (neutral), and they have nonpolar, hydrocarbon "tails".


Stereoisomers with two or more centers of dissymmetry and whose molecules are not mirror images of one another. Diastereomers have different chemical and physical properties. Also known as "diastereoisomers".

Diatomaceous Earth

Also know as Kieselguhr, diatomaceous earth is used in both column chromatography and also as a sample cleanup medium for the extraction of polar compounds. It is used as a support in liquid chromatography and is a weak adsorptive.


The process of solutes or particles spontaneously intermingling or dispersing in a liquid medium. In LC diffusion of the solutes in the column (bandspreading) has been defined by the van Deemter Equation. Outside the column, diffusion is determined by the sum of the contribution collectively referred to as Extra-Column Effects.

Diffusion Coefficient

Expressed in cm²/s, this is a parameter of a molecule in solution (Dm) or in the stationary phase (Ds). In partition chromatography with a liquid stationary phase, the symbol DL may be used to express this term. In gas chromatography where the mobile phase is a gas, the symbol DG may be used to express this term.

Diode Array Detector

UV-visible detector which uses a set of photodiodes to simultaneously measure absorbance over a wide range of wavelengths.

Diol Phase

A stationary phase used in both normal and reversed phase chromatography. The diol phase consists of a diol structure; two -OH groups on adjacent carbon atoms in an aliphatic chain. This can be used for reversed phase separation of proteins and peptides.


Also known as direct inlet probe or direct insertion probe. Used in Mass Spectrometry for a rod or tube having sample holder at one end, which is inserted into the vacuum system of the mass spectrometer through a vacuum lock. The sample cup is nested near to, at the entrance of, or within the ion source. A heater/sensor assembly heats the probe causing the sample to be vaporized into the source.

Displacement Chromatography

Refers to a method used in preparative HPLC, where a sample is placed on the head of the column and then displaced by a compound that is more strongly sorbed than the compounds in the original mixture. The sample molecules are displaced by each other and by the stronger sorbed compound, resulting in the eluting sample solute zones being sharpened.

Dissolved Gases

The presence of disolved gases (air) in HPLC solvents has several detrimental and time consuming consequences. Bubbles can form in the mixer, pump, column or detector cell, leading to flow instability, increased noise levels and reduced baseline stability. At low wavelengths oxygen can also cause increased background absorbance, decreasing detection sensitivity.

Distribution Coefficient

Commonly referred to by the term "Kd", the distribution coefficient is defined as the ratio of the equilibrium concentration of solute in the stationary phase to the concentration in the mobile phase. The latest IUPAC nomenclature for the distribution coefficient is "Kc".

Distribution Constants

The distribution constant is the concentration of a component in or on the stationary phase divided by the concentration of the component (e.g., associated and dissociated forms) in the mobile phase.


Abbreviation of dimethylformamide. MW 73.1, Boiling Point 153.0 C, Polarity Index 6.4, Solubility in water miscible in all proportions, UV cutoff 268nm. Common solvent used in gel permeation chromatography.


Abbreviation of dimethylsulfoxide. MW 78.13, Boiling Point 189.0 C, Polarity Index 7.2, Solubility in water miscible in all proportions, UV cutoff 268nm. Common solvent used in reversed phase chromatography and gel permeation chromatography. Exellent for removing strongly retained components (adsorbed chemical garbage) from reversed phase columns.

DP Number

The "degree" of polymerization; more specifically, the average number of monomer units per polymer unit.

Drain Valves

A valve used to direct the pump stream to waste for flushing or solvent changeover.

Drawout Plate

In Mass Spectrometry, part of the ion source which is positioned near the exit of the ionization chamber. A negative voltage is sometimes applied to the drawout plate to help pull ions out of the chamber.


In HPLC, drift refers to the slow non-random change in the level of the signal baseline over time. Under Isocratic conditions, a drifting baseline implies the column is not equilibrated or the composition of the mobile phase is changing over time due to, eg., solvent evaporation. Some baseline drift is normal with gradient elution due to changes in refractive index or absorbance.

Dry Packing

A method used to pack columns or cartridges where efficiency is not an issue. The dry sorbent is poured into the empty column or cartridge and tamped to settle the bed.

Dynamic Mixer

A Motor-driven mixer which mixes the mobile phase components after they emerge from a gradient former.

Eddy Diffusion Term

Refers to the A-term in the van Deemter equation. It is the contribution to plate height due to molecules travelling along different paths through the column, which depends on the particle size and the packing material in the column. It is also known as the multipath term. A = 2(lambda)dp.


Abbreviation of Ethylenediamine tetraacetic acid. EDTA is used as a metal chelator to bind/remove eg., lead and iron.

Effective Theoretical Plates

The true number of plates in a column (Neff). This corrects the theoretical plates for dead volume. Neff = 16(tr - tm)², where tm is the void time.


general term used to express the peak width produced by a column. Efficiency is measured in terms of the number of plates, N, the symbol for the number of theoretical plates. N is most commonly calculated as follows: N=16(tr/wb)², where tr is the retention time and wb is the width of the peak base.


The mobile phase leaving the column.

Effluent Splitter

In Mass Spectrometry, a device that splits the flow of a chromatographic column into two parts. The flow that is directed to the mass spectrometer is chosen to be compatible with the vacuum capacity of the mass spectrometer.

EI (Mass Spec.)

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.