This blog is part of our separation science primer series which provides an easy-to-understand overview of key topics in solid-phase extraction and chromatography.
This blog focuses on solid phase extraction (SPE) formats and terminologies used by us while describing our products, and processes. Similar formats and terminologies may be used by other scientists and vendors.
Formats and Terminologies
Solid Phase Extraction (SPE), is a sample preparation technology that utilizes chromatographic stationary phase material (media). SPE devices, packed with the media are available in various formats. Different names are used to describe the SPE devices for each format. Figure 1 below shows some common formats including:
SPE Columns. These devices are the widely used format. It is a simple cylindrical device made of plastic or glass packed with the media bed. Depending on the cylinder size, a sample of a certain volume is poured from the top which flows through the bed and passes at the bottom outlet.
SPE Cartridges. These devices are also cylinder-packed with the media. However, here there is typically very little or no space for additional sample. The sample is introduced by attaching a syringe from the top. A male female luer lock connects the SPE cartridge to the syringe.
SPE Pipette Tips. These devices employ micropipette tips packed with media. Depending on the micropipette tip volume, a sample of a certain volume is pulled from the bottom using a pipettor which flows into the bed and again pushed out from the bottom.
SPE Columns SPE Cartridges SPE pipette tips
Fig 1. Schematic diagram of SPE column, SPE cartridge and SPE pipette tip
Within each format, depending on how the media is packaged, additional terminologies could be used to further describe the SPE devices. These include:
Standard SPE. The media is powder-packed between two polymeric frits within a device. The analyte interacts with the media as the sample solution flows through the packed bed. This is the most common format.
Dispersive SPE. The media is loosely contained (dispersed) within a device. The loose media mixes with the analyte present in the sample solution. The resulting interactions between the media and analyte facilitate analyte recoveries. QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) dispersive SPE is a well-known sample preparation approach in pesticide residue analysis.
Monolith or fritless SPE. In this format, the spherical microbeads are chained together into a continuous three-dimensional network. This compactly packed uniform monolith bed improves mass transfer kinetics and analyte adsorption.
Additional terminologies could be used depending on the objectives for using SPE-based sample preparation:
Guard SPE. The devices employed to remove unwanted or interfering compounds or reduce ion suppression from a sample matrix are called guard SPE devices.
Trap SPE. The devices that concentrate analytes or fractionate the sample by class of compounds prior to analysis are referred to as trap SPE devices.
Fig 2. Schematic diagram of Inline Trap or Guard SPE
Finally, the terms used to describe an SPE device depending on how they are used in the workflow are:
Offline SPE. The samples prepared after SPE-based procedures are removed (manually or by automation) and injected into the analyzer.
Inline or online SPE. The SPE system is integrated with the analyzer to allow a direct seamless introduction of samples prepared after SPE-based procedures into the analyzer.
Fig 3. Images of NanoPak-C SPE columns, SPE pipette tips and SPE cartridge
We offer a suite of SPE products employing our award-winning NanoPak-C carbon microbeads for sample cleanup and preparation for LC analysis. These include:
Novel truly fritless monolith SPE columns
Custom products across these formats are also available.
Visit our store at www.millennialscientific.com/shop to learn more.