Chromatography Glossary



In mass spectrometry, part of the rotary-vane pump that traps and moves molecules.


A step in the validation of an analytical technique which checks that the performance specifications of the procedure can be attained. Performed between method development and routine use, and often regularly thereafter. In chromatography, verification will involve the use of a set of calibration standards.

Vicinal Silanol

Created when two free silanol groups in close proximity interact through hydrogen bonding.

Virtual Leak

In mass spectrometry, a leak that is not detectable from the outside of a mass spectrometer. If gas or liquid is trapped inside the vacuum envelope, it may leak out into the system. For example, air trapped under a gasket seal within the mass spectrometer will give a "leak spectrum" but is not detectable from the outside. These are virtual leaks; they will eventually pump away, but this may take days or even weeks.


A measure of resistance to solvent flow (cP).


Is the appearance of a space, usually at the head of the column, caused by settling or dissolution of packing material. A void in a column causes decreased efficiency and a loss of resolution. It can sometimes be removed by filling with glass beads or porous packing.

Void Time

Is the time for elution of an unretained peak.

Void Volume

Also known as Interstitial volume, Vo or Vm. Refers to the total volume of mobile phase in the column, the remaining space in the column being occupied by packing material. In porous material it includes the interstitial and intra-particle volumes. This volume can be determined by injecting an unretained substance into the column which measures the void volume plus the extracolumn volume.


To change a solid or liquid sample to a vapor. Typically, a sample must be in the vapor state before ionization can occur.

Wall Effect

Is the result of loose packing density near the walls of a column. Mobile phase has a tendency to flow slightly faster nearer to the wall because of decreased permeability. The solute molecules that are near the wall can move faster than the average of the solute band, causing bandspreading. This is not to be confused with the bandspreading effect of laminar flow in a straight tube, which shows a characteristic parabolic profile and also results in dispersion of the solutes.

Wall-Coated Open-Tubular (WCOT) Column

In these columns the liquid stationary phase is coated on the essentially unmodified smooth inner wall of the tube.


The distance measured along the line of propagation of a wave, between two nearest points which are in the same phase as the wave. Units are in angstrom (Å) or nanometers (nm). In LC, the electromagnetic region most often used for detection purposes is from 190 to 600nm, and is referred to as the UV-Visible range.

Weak Anion Exhanger

Abbreviation of weak anion exchanger. Also known as Polyethlyeneimine, PEI, Diethylaminoethyl, DEAE, or Weak Base. These are most useful for analyzing basic proteins and peptides.

Weak Cation Exhanger

Abbreviation of a weak cation exchanger. Also known as carboxymethyl, CM, Weak Acid Used in ion exchange chromatography, they are most useful for analyzing basic proteins and peptides.

Weak Solvent

A solvent which causes long retention times of sample components.

Width Change Parameter

User-selectable integrator or data system parameter which helps detect broad peaks which occur later in the chromatogram. Usually applied to isocratic separations.


The amount of solute (compound) recovered at the end of the process as a percentage of the amount present in the injected sample.

Zero Dead-Volume

In theory, a fitting which adds no extra-column volume to the system when making a connection.


A region in the chromatographic bed where one or more components of the sample are located. The term Band may also be used for it.


A zwitterion is a compound that carries both positive and negative charges in solution. Same as a dipolar ion. Some neutral amino acids are examples of zwitterions.