Chromatography Glossary



Noise is the general term for random variations in detector signal. Noise appears on chromatograms as an erratic baseline and can be classified as cyclic or random. Short-term noise (less than 1 sec) is often electrical in nature; long-term noise can be due to flow rate changes, temperature changes, or column "bleed".

Nominal Ion Mass

In mass spectrometry, the mass of an ion calculated using the integer value for masses of the most abundant isotope (C=12, H=1,....).

Non-Ionized Species

A term used in mass ppectrometry for sample molecules and fragments that are not ionized.


A molecule or solvent in which the electrical charges are more or less symmetrically distributed around the center. In LC, nonpolar is used interchangably with the term "hydrophobic" which implies the tendency of the molecule or solvent to avoid solvation by water. Nonpolar molecules such as polyaromatic hydrocarbons are often analyzed by reversed phase chromatography. Nonpolar solvents such as hexane are typically used in normal phase chromatography.

Non-polar Molecule

A molecule with a symmetric distribution of charge. Typically used as a more generic term to include even moderately polar molecules and sorbents that may, in fact, not be totally symmetrical in terms of their charge distribution.

Non-porous Particle

Is a solid particle which has no pores. Often used as a support for porous coated or bonded phase.

Non-Specific Binding

Binding refers to binding of a protein or other solute to an HPLC column by some mechanism other than that of the column design.

Normal Phase

Extraction mode relying upon intermolecular hydrogen bonding and polar dipole-dipole interactions for retention in which moderately polar to polar molecules are extracted from a non-polar solvent using a polar sorbent.

Normal Phase Chromatography

Refers to a polar stationary phase and a nonpolar mobile phase. It also refers to the use of polar bonded phases eg CN.


Normalization is a quantitative method commonly employed when the entire sample is eluted from the column. The area percent is taken as weight percent composition. Normalization is of limited usefulness since most detectors give different responses to different samples.


The most commonly used funcional group on reversed phase bonded silicas. Also known as C18.


A term used in mass spectrometry to describe the position of the scan line of a stability diagram. The lower the offset, the wider are the peak width.

Oil Charge

In mass spectrometry, the quantity of oil in a diffusion pump.

Oil Pump

In mass spectrometry, a small pump that transports oil in a rotary-vane pump.

Open-Split Interface

In mass spectrometry, a split inlet implementation utilizing a purge flow which is typically the same as a carrier gas. Only allows a small portion of the sample to enter the mass spectrometer.

Open Tubular Columns

These are columns of small internal diameter, used in HPLC, SFC and capillary electrophoresis. Stationary phases can be bonded to the internal wall of the column. The most common type used is the fused silica capillary with internal diameters ranging from 0.050 to 0.9mm.

Optical Activity

The property of a molecule involving rotation of plane-polarized light.

Optical Isomer

A molecular configuration which is not superimposable with its mirror image.They are now more commonly known as chiral or enantiomeric molecules, since most optical isomers lack optical activity at some wavelengths of light.

Optical Purity

The percent of one enantiomer in excess of the other, as determined from optical rotation measurements.


The process by which a method is developed in order to minimize separation run time and cost and maximize resolution and efficiency.


A compound that contains one or more carbon atoms.

Organic Modifier

Is an organic solvent, which is miscible in water, added to an aqueous mobile phase to produce a separation in reversed phase HPLC.


Patented grafting process which incorporates uniform stabilizing ethane cross-linking to provide resistance to high pH attack while maintaining mechanical strength of the core-shell or fully porous particle.


A term used in mass spectrometry to describe the motion of an ion in a quadrupole. Usually a complex periodic motion.

Outlet Check Valve

The check valve in an LC pump that allows mobile phase to flow to the column from the pump, but not in the reverse direction.


The capability of a computer data system to display or plot two or more chromatograms on top of one another.


When the column capacity is exceeded, the column is said to be overloaded. It is defined as the mass of sample injected onto the column at which the efficiency and resolution begin to be affected if the size of the sample is continuously increased.


The stationary phase particles used to pack a chromatographic column.

Packing Materials

The component that is placed inside the column or cartridge. Once packed, the packing material is where the separation occurs during a chromatographic run. The terms sorbent, stationary phase and packing bed are synonymous with packing material.

Parent Ion

A term used in mass spectrometry for an ion that produced product ions. Product ions are formed as a result of fragmentation of the parent ion.

Partial Pressure

A term used in mass spectrometry for the pressure contribution due to each component of a mixture of gases.

Particle Beam

In mass spectrometry, an interface used to connect a liquid chromatograph to a mass spectrometer. This interface is used with the standard EI or CI ion source. A system with this type of interface produces spectra similar to a GC/MS system; this is a distinct advantage over other LC/MS techniques.

Particle Size

This term refers to the average particle size (diameter) in a column.

Particle Size Distribution

This is a measure of the distribution of particles packed in a column. In HPLC, it is preferable to have narrow particle size distribution.


Refers to small solid particles in the sample or mobile phase; these particles can plug the column or other parts of the HPLC system.

Partition Chromatography

Is a separation process where one of the liquid phases is held stationary on a solid support, while the other can flow down the column freely. Solutes partition themselves between the two phases based on their own individual partition coefficients.

Partition Coefficient

Denoted by the symbol K, the Partition Coefficient Is the amount of stationary phase relative to the amount of solute in the mobile phase. Can also be known as distribution coefficient (Kd).

Parts Per Million

An expression for concentration; one part of the substance per million total parts. Commonly used in environmental analysis.

Pascal ( Pa.)

The standard unit of pressure corresponding to a force of 1 Newton per square meter (1N/m2). 1Pa = 7.5 x 10^-3 Torr.


Peak is the elution band; a part of a differential chromatogram recording the detector response or eluate concentration of a single component. Ideally peaks are sharp, Gaussian shaped.


Peak is the elution band; a part of a differential chromatogram recording the detector response or eluate concentration of a single component. Ideally peaks are sharp, Gaussian shaped.

Peak Area

Peak Area refers to the area lying between the peak outline and the peak base in the chromatogram. Used to quantitate the concentration of sample components.

Peak Capacity

The maximum number of components that can be separated when a maximum k and a minimum R value are specified.

Peak Height

Height refers to the distance between the peak maximum and the peak base in the chromatogram. Used to quantitate the concentration of sample components.

Peak Symmetry

Is a factor describing the shape of a chromatographic peak. In theory it is assumed that there will be a Gaussian shape and that peaks are symmetrical. The peak asymmetry factor is the ratio (at 10% peak height) of the distance between the peak apex and the back side of the chromatographic curve and the front side of the curve.

Peak Volume

The volume eluted in the time span of one baseline band width.

Peak Width

Usually refers to the time or distance at the baseline between extrapolated tangents to the peak drawn at the inflection points. Also refers to the width of a peak measured at a specified fraction of its total height. Peak width is also known as band width.


Abbreviation of Polyetherether Ketone. A relatively stiff, chemically-resistant plastic that is popular as a construction material in metal-free chromatographs. Material Compatibility and Uses: Used to make pump parts, fittings and connecting tubing. Compatible with almost all organic solvents. Useful in most high pressure situations up to 5000psi due to PEEK's high mechanical strength. Registered trademark of ICI Americas.

Pellicular Packing

Packing Material with a solid core (eg., a glass bead) enveloped with a porous material.

Percent Recovery

A measure of accuracy that is calculated as the measured value relative to the true value, expressed as a percent.

Perfusion Chromatography

Similar to HPLC and LC, Perfusion Chromatography is based on a flow-through particle which contains two classes of pores: 1. through-pores large enough to allow for convective flow through the particle, and 2. smaller, diffusive pores lining the through-pores which provide high surface area where the separation process takes place.


A measure of the quality of a column or cartridge, taking into account both the packing material and the way it was packed. High permeability values indicate a poorly packed column (excessive interstitial volume), whereas low permeability values indicate possible blockage of the column, tubing or other system component.