Chromatography Glossary


Thermal Emission

A term used in Mass Spectrometry for the emission of electrons from a heated filament.

Thermocouple Gauge

A thermal coductivity gauge used in Mass Spectrometry to measure pressures in low vacuum regions. This low vacuum gauge directly measures the temperature of the wire with a thermocouple.

Thermospray Interface

In mass spectrometry, an interface connecting an LC to an MS that uses a heated capillary vaporizer tube. An ionization reagent, typically ammonium acetate, must be added to the LC mobile phase. Spectra produced by thermospray resemble those from CI.


Abbreviation of Tetrahydrofuran. MW 72.11, Boiling Point 66.0 C, Polarity Index 4.0, Solubility in water miscible in all proportions, UV cutoff 190nm. Common solvent used in reversed phase and normal phase chromatography as well as gel permeation chromatography (GPC).


A term used in mass spectrometry for a data acquisition or tune parameter that specifies the minimum size of a signal so that it is recorded. Signals that are smaller than the threshold are considered to be noise.


Refers to the number of samples analyzed or the amount of sample processed over a given span of time.


In mass spectrometry for total ion chromatogram. The chromatogram produced by a plot of the summation of all ion abundances versus time.

Time Constant

Refers to electronic noise smoothing circuitry. The larger the time constant, the greater the smoothing.

Time Of Flight (TOF)

In mass spectrometry, a type of mass filter that measures the flight time of ions with an equivalent kinetic energy over a fixed distance.


An alternative to stainless steel when a biocompatible metal part is required in HPLC. Titanium is considered to be physiologically inert. Similar strength to stainless steel but 45% lighter. The metal has high temperature stability and excellent resistance to dilute sulfuric and hydrochloric acids, most organic acids, and concentrated salt solutions - including chlorides. Titanium is more brittle than than stainless steel and care should be taken when bending the tubing. Capillary tubing should not be used with acids due to the potential of cracking.


Abbreviation of thin-layer chromatography.


TMS is an abbreviation of Trimethyl Chlorosilane, a common silylation reagent employed in the formation of derivatives, and in deactivation of packing materials.


In mass spectrometry, a unit for measurement of pressure. Defined as the pressure required to support a column of mercury 1-mm high.


Is covered by the A-term of van Deemter's equation. It is a property of a packed column that indicates the degree of unevenness of the route taken by the solute molecules as they pass through the column.

Total Ion Chromatogram

Refers to an output mode of the mass spectrometer detector, where the "chromatogram" is plotted using the sum of the intensities of all the measured ions in the spectrum as the ordinate. Sometimes referred to as Total Ion Monitoring (TIM).

Total Permeation Volume

This refers to the retention volume in which all molecules that are smaller than the smallest pore will be eluted, ie all of the molecules will totally permeate all of the pores and elute together, at Vp.

Trace Enrichment

Trace amounts of compounds from weak mobile phase or solution are retained on packing material and are then eluted by the addition of a stronger mobile phase in a concentrated form. The technique is most successful in the concentration of trace amounts of hydrophobic compounds out of water using a reversed phase column. A strong solvent such as acentonitrile is required to elute the enriched compounds.

Traditional Quadrupole

In mass spectrometry, four independent rods (which may be made of molybdenum) that function as a mass filter when the appropriate dc and RF voltages are applied. The rods may be round or hyperbolic.


Manual peak area measurement technique which approximates the area of a peak by measuring the area of the triangle constructed from the baseline and lines drawn through the inflection points.


Most HPLC systems are plumbed with 1/16" OD tubing. The choice of tubing material is based on its chemical resistivity. Stainless steel should be avoided if the mobile phase contains high levels of strong acids or halogenated salts. PEEK is useful with most solvents, but should be avoided when THF, chlorinated solvents, or high concentrations of acids are used. Titanium is virtually inert to most chemicals and biocompatible too.

Tubing Stop

A shoulder within a tube fitting against which the tube is pressed to form a gap-free connection.


A setup process that calibrates and adjusts the instrument. During tuning, the relative and absolute abundances are established and the mass assignment, resolution, and spectral peak widths are set.

Turbomolecular Pump

In mass spectrometry, a high vacuum pump using a set of rotating and stationary blades to direct molecules through the system.

Two-Dimensional Chromatography

A procedure in which parts or all of the separated sample components are subjected to additional separation steps. This can be done e.g., by conducting a particular fraction eluting from the column into another column having different separation characteristics.

Ultimate Vacuum

A term used in Mass Spectrometry for the highest vacuum that can be obtained in a system when all inlets have been capped off.


Ultraviolet is that portion of the electromagnetic spectrum just beyond violet on the short-wavelength side, generally from 100 to 4,000Å (10 to 400nm). It is broadly used in LC, however, to include the visible range of the spectrum (from 190 to 600nm).

Ultrahigh-performance liquid chromatography (UHPLC)

Ultrahigh-performance liquid chromatography is often used for any separation performed at pressures greater 400 bar.


An HPLC fitting used to connect two pieces of tubing, generally of the same outer diameter (OD).

Universal Detector

A detector which responds to every component in the column effluent except the mobile phase.

Upper Control Limit

The upper limit in a control chart indicating when the controlled parameter is out of specification. Usually defined as equal to the mean plus three standard deviations.


USP is an abbreviation of United States Pharmacopeia.

UV Absorbance

The amount of ultraviolet light absorbed by the sample.

UV Cut-Off

The wavelength at which the solvent has an absorbance of 1.0 in a 1cm cell. Below this wavelength, the solvent cannot be used with the UV detector.

UV Detector

UV Detector is by far the most common HPLC detector. Sometimes referred to as a UV-Vis(ible) detector, the UV Detector detects the amount of light energy absorbed by an analyte at a given wavelength or wavelengths. Three types of UV detectors are common: fixed wavelength, variable wavelength and diode array.

Vacancy Chromatography

Is a technique in which a mobile phase additive causes a relatively high detector signal output. When a solute is eluted form the column, the strength of the signal is lessened and thus a "negative peak" or "vacancy peak" is created.

Vacancy Peak

A negative peak, usually caused by a sample band passing through the detector which is less responsive (ie., with lower signal output) than the mobile phase.


In mass spectrometry for any pressure below atmospheric pressure.

Vacuum Degas

A modular electical HPLC accessory placed between the eluent resevoir and the pump. Between its' inlet and outlet ports there are many metres af gas permeable tubing. The gas permeable tubing is coiled inside a vacuum chamber. As the pump draws the solvent, it passes slowly through the tubing and the dissolved gasses are drawn into the vacuum chamber. The emerging solvent reaches the pump almost totally free of dissolved gas.

Vacuum Gauge

Gauges used in Mass Spectrometry to measure pressure within the vacuum region.

Vacuum Seal

In mass spectrometry to join parts,seals are impassable to gas flow and made of soft material which match the mating surface. Two types of seals commonly used are demountable and moving.

Vacuum System

In mass spectrometry, all the components associated with lowering the pressure in a mass spectrometer. This includes pumps, valves, gauges, seals and vacuum manifolds. Encloses the ion source, mass filter, and detector in vacuum. Necessary to help ions move from the ion source to the detector without colliding with other ions, sample molecules, air, or water.


A documented program that provides a high degree of assurance that a specific process, method, or system will consistently produce a result meeting pre-determined acceptance criteria.

Validation Test

A test run on an HPLC column to provide evidence that the column in good working order or is suitable for a particular application.

Van Deemter Equation

This equation is used to explain the concept of band broadening in chromatography. It represents the height equivalent of a theoretical plate and has three terms.

  • The A-term is used to describe Eddy diffusion, which allows for the different paths a solute might take when passing over particles of different sizes.
  • The B-term is for the molecular or logitudinal diffusion of the solute as it passes through the column.
  • The C-term is mass transfer and allows for the finite rate of transfer of the solute between the stationary and mobile phases.h = A + B/v + Cv.

Van Der Waals Forces

An intermolecular interaction which ocurs whenatoms of two different molecules are sufficiently close that the temporary dipoles caused by electronic vibrations in one molecule induce dipolesin neighbouring molecules. This short rangr force is relatively weak (0.5 to 1 kcal/mole) and increases in magnitude with molecular weight..