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What Is a Solid Phase Extraction?

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  • Written By: Lisa Mooney
  • Edited By: A. Joseph
  • Last Modified Date: 17 September 2014
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Solid phase extraction (SPE) is the name of a process that separates solid and liquid substances in a chemical solution. The extraction is most often accomplished by passing the sample through a column that is packed with a sorbent, which allows the liquid to pass through the apparatus while the solid remains are collected above. The purpose of solid phase extraction is to concentrate and purify samples for further study. These analytes might be contained in the solid or liquid matter. If the solid is the material to be analyzed, it will then be purified by a solvent rinse.

A general solid phase extraction utilizes a disposable cartridge that resembles a medical syringe. This cartridge sits atop a vacuum manifold to maximize the rate at which the solvent flows through the column. The cartridge contains C18-silica, which acts as a sorbent and is held in position with frits. A collection tube is positioned below the SPE column to receive the liquid removed from the mixture.

The chemist typically uses a four-step process when performing a SPE. The first step involves equilibrating the cartridge by wetting the surface with a solvent that is non-polar or only slightly polar. This accomplishes penetration of the covalently bonded phase so that separation can begin.

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Secondly, water or a buffer similar in nature to the sample that is being used is applied to the column. This liquid washes the entire column. It also saturates the cartridge's silica surface, which might begin to dissolve.

Only in the third step is the actual sample placed in the cartridge. The sample passes through the extraction process' stationary phase, and the analytes begin to interact and stay on the column's sorbent material. The liquids, including the salts, solvent and various impurities, proceed through the column to be collected in the receptacle below. A vacuum apparatus might be employed to help facilitate the process.

The final step has the column eluted, or washed, again to remove additional impurities from the cartridge, which contains the sample. The elution that is used is a buffer that has the proper potenz hydrogen (pH) level or a solvent that is non-polar. The analyte is then ready for further chemical analysis.

Solid phase extraction is often considered preferable to liquid-liquid extraction because it takes less time and can be less expensive. SPE is similar to chromatography in that a liquid mixture is dispensed through a packed column that removes analytes and impurities. The procedure can be accomplished on a large scale using manifolds to hold multiple columns so that several samples can be processed simultaneously.

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