Chromatography Glossary


Spectral Tilt

In mass spectrometry, the relative amount of high mass ions to low mass ions for a given compound. The spectral tilt is determined during tuning.

Spherical Packing

Refers to spherical solid packing material. These are preferred over packings containing irregular particles. Spherical particles pack more efficiently resulting in higher plate counts.

Split Inlet

A term used in mass spectrometry for an inlet that allows only a portion of the sample flow to enter the ion source. A restrictor is placed between a GC column and the vacuum system to restrict or split the column flow.

Split Peak

Split Peak is a chromatographic peak which does not exhibit a single maximum, but two instead. A split peak appears similar to a narrow capital M. Cause of split peaks include: a voided HPLC column, contamination on the column inlet, or sample solvent incompatibility with the mobile phase.

Stability Diagram

In mass spectrometry, a graph showing regions of stability and instability in terms of RF and DC values.


In mass spectrometry, the part of the difusion pump in which vapors travel upward to be forced through jets. The stack, located in the center of a diffusion pump, is made up of a series of concentric cylinders.

Stainless Steel Tubing

Stainless steel (SS 316) tubing employed for analytical HPLC is designed thick enough to withstand 12000 psi (816 atm) during packing of columns, is temperature stable and can withstand a broad range of pH in aqueous solutions. However the presence of halides, particularly in acid solution causes corrosion and pitting.


A sample with a known concentration of some compound X that is to be determined by an LC procedure. The concentration of X in a sample is determined by comparing it's peak size with the peak size of the standard.

Standard Addition

Standard Addition is a method of quantitative analysis where standard amounts of sample are added to the unknown; from the increase in peak height the concentration in the unknown can be estimated.

Standard Curve

A curve that plots concentrations of known analyte standards versus the instrument (detector) response to the analyte. Calibration standards are prepared by diluting the stock analyte solution in graduated amounts that cover the expected range of the samples being analyzed. The calibration standards must be prepared by using the same type of eg., acid or solvent at the same concentration as for the samples following sample preparation..

Standard Deviation

Standard Deviation is a statistical calculation describing the dispersion of a sample around its mean value, being a square root of the sampling variation.

Static Mixer

A device for mixing the eluents, delivered by a gradient former, that has no moving parts.

Stationary Phase

A stationary phase consists of a solid support which may have chemical functional groups or compounds physically or chemically bonded to its surface. The mobile phase is forced past the stationary phase under pressure and the solutes partition between the two phases according to the their distribution coefficients and rates of mass transfer.

Stationary-Phase Volume

The volume of the liquid stationary phase or the active solid in the column.


Part of the rotary-vane pump where the rotor is mounted that lubricates and provides a sealing surface.

Stator Blades

In mass spectrometry, stationary blades in the turbomolecular pump which are mounted to the walls to help direct molecules into the rotor blades.


The portion of an integral chromatogram recording the amount of a component, or the corresponding change in the signal from the detector as the component emerges from the column.

Step Gradient

Changing the mobile phase composition in step-wise increment, using a pump or selector valve.

Steric Hindrance

A condition in which a reaction or interaction is slowed, stopped or prevented because of the size of the chemical groups near the reaction site causes a blocking of approach to the site. Steric hinderence can be one point of interaction contributing to the resolution of enantiomers in chiral chromatography.

Strong Solvent

A solvent which causes early elution of sample components.

Supercritical Fluid Chromatography

Abbreviated SFC. This technique involves the use of an HPLC column (usually a small-bore ID column) with supercritical fluid as the mobile phase. It is used to separate substances that cannot be dealt with effectively by LC, because of detector difficulties, or in gas chromatography, because of the lack of volatility.


Support refers to solid particles. It can be uncovered or coated, or can have a chemically bonded phase.

Support Material

The material to which the bonded phase is applied.

Support-Coated Open-Tubular (SCOT) Column

A version of a PLOT column in which the porous layer consists of support particles and was deposited from a suspension.

Suppressor Column

A column or device which reduces eluent conductivity in ion chromatography by converting the eluent salt to a non-ionized or partly ionized form.

Surface Area

In an adsorbent, the surface area refers to the total area of the solid surface.

Surface Coverage

A measure of the extent of bonding of the available silanols on a sorbent surface. Expressed in μg/m2.


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 detergents.


An organic compound similar to the analyte of interest in chemical composition, extraction and chromatography, but not normally found in environmental samples. The surrogate standard is spiked into quality control blanks, calibration and check standards, samples and spiked samples before analysis. A percent recovery is calculated for each surrogate.


Is a process in which resins and gels increase their volume because of the solvent they are in. Solvents enter ion exchange resins to dilute ions. In gels they penetrate the pores. If swelling occurs in the packed column, a blockage or increased back pressure will also occur. This would also affect column efficiency.

Switching Valve

Switching Valve is a valve used in HPLC to re-route the mobile phase flow during the chromatographic run to perform backflushing, fraction cutting, to toggle between two columns or sequential analysis of a sample.

Syringe Pump

Syringe Pump is a popular and useful pump design for Micro-LC and SFC, consisting of a single, large volume cylinder and piston assembly (typically 50 mL in volume), such that uninterrupted mobile phase flow is available without pulsation.

System Peak

A chromatographic peak that is not a component of the sample but derives from a change in eluent composition caused by the sample.

System Suitability Testing

The name given to the process of checking that a particular analytical system meets the required analytical performance and gives the expected result for a known standard.


Asymmetry factor of >1, creates skew on the down side of a normal Gaussian peak. Caused by the sites on the packing material having a stronger than average retention for the solute.

Tailored Gradient

Gradient profile in which the strong solvent is increased in a way specifically designed for a particular sample or method.


A term used in Mass Spectrometry for part of the ion source positioned across from the filament in the ionization chamber. The target has a positive potential, which attracts electrons across the ionization chamber.

Target Compound

A specific compound of interest that is to be quantified in a sample.

Target Compound Analysis

In mass spectrometry, an acquisition (either SIM or scan) to look for and quantify certain predefined components.


Abbreviation of Triethylamine, a common mobile phase modifier added to improve the peak shape of basic compounds in reversed phase chromatography. TEA is also used sometimes as an additive in gel permeation chromatography.


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


Tefzel is Abbreviated ETFE. Material Compatibility and Uses: Similar to Teflon but not recommended for use with chlorinated solvents. Registered trademark of E.I. Dupont de Nemours & Co., Inc.

Temperature Programming

During a separation, the temperature is changed as a function of time.

Temperature Sensitivity

Refers to detectors which respond to small changes in temperature, eg., refractive index, amperometric and conductivity detectors.

Ternary Eluent

Eluent mixture containing three solvents. Ternary eluents usually contain one weak solvent and two strong solvents.

Ternary-Solvent Mobile Phase

A mobile phase composed of three solvents (e,g,, methanol, water and acetonitrile.) Also called ternary mobile phase.

Test Chromatogram

The first chromatogram run, usng a standard, on a new HPLC column. Sometimes referred to as a "Reference Chromatogram".


Abbreviation of Trifluoroacetic acid, a mobile phase modifier added to enhance selectivity and improve peak shape in reversed phase and size exclusion chromatography.

Theoretical Plates

The number of theoretical plates, N, is a measure of column efficiency. 'N' is calculated by squaring the ratio of the retention time to the baseline peak width and multiplying by 16.

Thermal Conductivity Gauge

In mass spectrometry, a class of pressure gauges used to measure pressure in low vacuum regions. Commonly used thermal coductivity gauges are the Pirani and the themrocouple gauge.