Chromatography Glossary


Preparative Column

A larger-diameter column used for recovering purified materials by chromatographic separation.


Inlet Pressure (pi ): The absolute pressure at the inlet of a chromatographic column.

Outlet Pressure (pO ): The absolute pressure at the exit of a chromatographic column. It is usually but not necessarily equal to the Ambient Pressure (pa), the atmospheric pressure outside the chromatographic system.

Pressure Drop (Dp): The difference between the inlet and outlet pressures:
Dp = Pi - PO

Relative Pressure (P): The ratio of the inlet and outlet pressures:
P = Pi/PO

Pressure Drop

The pressure measured at the inlet minus the pressure measured at the outlet of a component in the chromatograph.

Pressure drop is related to:
1. Column dimensions
2. Particle Size
3. Flow rate
4. Mobile phase viscosity (temperature-dependent)


The act of filling the fluid channels within the pump with eluent.

Process Validation

Establishing documented evidence that provides a high degree of assurance that a specific process will consistently produce a product meeting its predetermined specification and quality characteristics.

Profile Scan

In mass spectrometry, a mass spectral scan that retains all the data points collected near the m/x specified. The data is presented as a smooth curve. In a normal mass spectrum, the data presentation is simplified by placing a single line at the peak maximum.

Proton Affinity

In mass spectrometry, a mass spectral scan that retains all the data points collected near the m/x specified. The data is presented as a smooth curve. In a normal mass spectrum, the data presentation is simplified by placing a single line at the peak maximum.


PSI is an abbreviation of Pounds per square inch, one of the more common units for measuring and reporting pressure drop across the HPLC system.


Teflon is sometimes abbreviated PTFE, TFE, poly(tetrafluoroethylene). Material Compatibility and Uses: Inert to all HPLC solvents, acids and bases. Used in low pressure applications. Inherently hydrophobic. Registered trademark of E.I. Dupont de Nemours & Co., Inc.

Pulsating Flow

Is the flow that originates from a reciprocating pump. Usually these pulses are dampened out by a pulse damper or electronic pressure feedback circuit. Some electrochemical detectors are affected by these pulses.


A periodic or recurring cycle of alternating increase and decrease of a measured parameter. eg baseline, pressure, volume, voltage etc.


The mechanical device used to draw solvent into the liquid chromatograph and pump it through the system under high pressure. There are several types of pumps commonly used:

  • Single piston reciprocating pump
  • Dual piston reciprocating pump
  • Hybrid dual piston reciprocating pump
  • Diaphram pump
  • Syringe pump
  • Pneumatic Pump

Single and dual piston pumps are most commonly used in analytical and prep HPLC. The syringe pump has been used for Micro LC work due to pulse-free flow and good control over micro-volume delivery.

Pump Exhaust

The part of a rotary-vane pump opposite the inlet. The flow rate at the exhaust outlet is used to measure the rate of carrier or mobile phase and the reagent gas as it moves through the mass spectrometer.

Pump Head

The liquid end, or wetted parts of the pump. Normally comprised of a stainless steel (or inert) barrel, housing a synthetic sapphire piston, a plastic seal, and a metal spring arrangement; plus up to two check valves.

Pump Preload

A device used just after some pumps to maintain enough back pressure for reliable check valve operation.

Pumpdown Mode

An automatic or manual procedure that occurs after a mass spectrometer is turned on and the internal pressure goes from atmospheric to operating pressure.

Pumping Speed

The amount of gas at a specified pressure pumped away by the pumping system, expressed as a volume per unit time (ml/min.).

Pumpout Valve

In mass spectrometry, a valve used with isolation valves to bring the source and analyzer manifold to the rough vacuum before opening the isolation (butterfly) valves.

Purge and Trap Thermal Desorption

Routinely used for volatiles in environmental (EPA 8260, 502.2,524.2, 624,) and food samples.

Purge valve

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

Purge valve

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


The act of flushing the pump and flow path with eluent. Usually done at high flow rate.

Purification Procedure

A process, such as crystallization distillation or chromatography, intended to improve the purity of an intermediate or of an API (active pharmaceutical ingredient).


Polymerized and cross-linked polymer gel (based on ethanol homopolymer) used as a separation medium in biochromatography. It is used in bead form in gel permeation chromatography which have aqueous mobile phases (GFC).


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.

Qualifier Ion

An ion used to confirm the identity of a given compound. The qualifier ion is chosen for it's specificity for the given compound.

Qualitative Analysis

The determination of which compounds are present in a sample. In LC this is usually done by comparing retention times for bands in the unknown sample with retention times for various pure compounds suspected to be present in the sample.

Qualitative Applications

An application designed to determine the identity of a sample. In general, the mass spectrum of the "unknown" is compared with that of a reference spectrum to verify the identity.

Quality Assessment

Ways in which an analysis is monitored to infer the quality of the data.

Quality Assurance

Abbreviated QA, Quality Assurance is all those planned and systematic actions necessary to provide adequate confidence in laboratory results. In chemical analysis, QA refers to the steps taken to provide assurance that an analysis meets the expected level of quality. QA includes Quality Control and Quality Assessment.

Quality Control

Abbreviated QC, Quality Control incorporates those quality assurance actions that provide a means to control and measure the characteristics of measurement equipment and processes in order to meet established requirements. In chemical analysis, QC refers to the steps taken to achieve the expected level of accuracy and precision.


The determination of the amount of a compound present in a sample. Before quantification, the compound must be identified and known amounts of authentic compounds (standards) must be analyzed to determine the response of the instrument. Also known as "quantitation".

Quantitation Ion

One of the most abundant ion from a given spectra that is used for quantitation in SIM or target analysis.

Quantitative Applications

An application designed to determine the amount of a given component in a sample.

Quantitive Analysis

The analysis of a sample in order to determine the concentration of different compounds in the sample. Quantitive analysis in LC is usually based on the size of the bands in the sample chromatogram (peak height or area) compared to band size in a sample known concentration (the calibrator or standard).


A mixture having no optical activity which consists of equal amounts of enantiomers.

Radial Compression

The use of radial pressure applied to a flexible-wall column or cartridge to lessen wall effects. Radial compression eliminates bubbles, voids, and channels, producing a more dense packing bed, which allows for faster flow rates and improves resolution.

Radial Diffusion

Describes the diffusion across the column in a radial direction. On injection into a column, the sample spreads radially as well as in the longitudinal direction of flow.

Radio Frequency Power Amplifier (RFPA)

The RFPA is part of the quadrupole electronics that amplifies the signal and applies it to the quadrupole rods.

Radioactive Detector

Most commonly used in the pharmaceutical industry to trace the metabolism, disposition and elimination of drugs, radioactive elements (isotopes) are incorporated into the test drug molecule, and their beta- or gamma-ray emssions monitored either on-line during an HPLC or off-line by after fraction collection.


Chromatography in which the identification of constituents of a separated mixture is aided by adding radioactive isotopes.

Raw Material

Any ingredient intended for use in the production ofactive pharmaceutical ingredients. These include starting materials, intermediates, process aids, and solvents.

Reaction Chromatography

A technique in which the identities of the sample components are intentionally changed between sample introduction and detection. The reaction can take place upstream of the column when the chemical identity of the individual components passing through the column differs from that of the original sample, or between the column and the detector when the original sample components are separated in the column but their identity is changed prior to entering the detection device.


A substance, other than the starting material or solvent, which is used in the manufacture of an active pharmaceutical ingredient or intermediate.