Glossary of Solid Phase Extraction

Analyte
Compound to be isolated and measured in a sample preparation scheme

Column Volume
The sum of the interstitial volume plus the pore volume of the sorbent within the column

Bonded Phase
An organic functionality covalently bonded to a chromatoghraphic support.

Breakthrough
Lack of analyte retention which occurs when the total mass of the solutes (analytes + interferences) exceeds the capacity of the sorbent or the solute is weakly retained

Buffer
A solution of a weak acid and its salt or a weak base and its salt which can resist pH change upon addition of small amounts of strong acid or base

Capacity
Total quantity of solutes (analytes & interferences) which can be retained from a specific sample matrix solution by a given mass of sorbent

Conditioning
The preparation of the extraction column to receive the sample. For reversed phase columns, this involves the application of a solvent such as methanol, followed by a similar volume of water. Normal phase columns are conditioned with a solvent similar to the sample solvent. Ion exchange columns are conditioned with a buffer of appropriate pH and ionic strength.

Counter Ion
The ionic species which pairs or associates with the ionic functional group of opposite charge on an ion-exchange sorbent. To be retained, a charged analyte must displace the counter ion associated with the ion exchanger group.

Eluent
Solvent or solvent mixture used for the removal of the solutes from the sorbent bed.

Elution Volume
The volume of solvent required to elute an analyte quantitatively.

Endcapping
A technique used to remove unwanted silanol groups on the surface of the silica which might otherwise undergo secondary interactions with the solutes.

Extraction
Transfer of the analytes from one phase to another

Frit
The porous element which contains the media within an SPE column. The frits are typically manufactured from porous polyethylene or polypropylene

Hydrophilic
"Water loving": Refers both to stationary phases that are compatible with water and to water soluble molecules in general

Hydrophobic
"Water hating": Refers both to stationary phases that are not compatible with water and to molecules in general that have little affinity for water. Hydrophobic molecules have few polar functional groups: most are hydrocarbons or have high hydrocarbon content.

Interference
Substance in the sample or separation system which may influence retention of the analyte on the sorbent or may co-elute with the analyte and influence analytical determination

Ion Exchange Chromatography
A chromatographic mode in which ions are retained by oppositely charged groups covalently bonded to a solid support. The analyte ions are retained by displacing counterions associated with the bonded functional group.

Liquid / Liquid Extraction (LLE)
A purification technique whereby the sample is first dissolved in a solvent and then agitated with a second immiscible solvent . Solutes that partition preferentially with the second solvent are extracted and effectively purified.

Matrix
All components of the sample including the solvent, but excluding the analytes

Mobile Phase
The solvent that moves the solute through the column

Non-Polar Molecule
Molecule with a symmetric distribution of charge

Normal Phase
A mode of chromatography whereby retention on a sorbent bed increases with the polarity of the sorbent. Sorbents used in this mode include silica, florisil and aminopropyl.

pKa
The pH value at which fifty percent of the ionisable groups of an ionic analyte are ionized and fifty percent are in the molecular form

Polar Molecule
Molecule with an unsymmetric distribution of charge

Pore Size
The average diameter of the porous openings on the surface of a sorbent particle

Reversed Phase
A chromatographic mode in which non-polar to moderately polar analytes are extracted from a polar solution using a non-polar sorbent

SAX
Strong anion exchanger

SCX
Strong cation exchanger

Solid Phase Extraction
Solid Phase Extraction (SPE) is a broad term used to describe the separation technique where liquids contact modified solid surfaces and a component of the liquid adheres to the solid. In a separate step, the solid releases the component. The solid usually consists of an inert core covered with unique "hooks" that remove the targeted material from the starting liquid.These active solids are packed into containment devices such as plastic columns through which the matrix and subsequent wash & elution solvents are passed to produce a purified material.

Sorbent
Bonded phase silica or adsorbent used as the stationary phase in SPE


Surface Area
The surface area on the surface and wthin the pores of a chromatographic sorbent. This is normally expressed as m2/g