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Solid Phase Extraction

Solid phase extraction (SPE) is a method of sample preparation that concentrates and purifies analytes from solution by sorption, followed by elution of the analyte with a solvent appropriate for instrumental analysis, such as LC-MS. Porvair Sciences offers a complete range of products to implement SPE. MicroLute™ is the original 96-well plate format for SPE. This device consists of a polypropylene 96-well plate loaded with a choice of sorbent and sorbent volumes. The frits have a mean pore size of 20 microns and are made from microporous high-density polyethylene.

What is Solid Phase Extraction (SPE)?

SPE is an method of sample preparation which chemically separates the individual sample components in a liquid mixture based on their chemical and physical properties. n most cases, samples are in a liquid state, and go through the process of SPE so that the individual compounds can be chromatographically separated.

This sample preparation technique is commonly used in analytical labs to extract and concentrate analytes from a complex matrix. SPE helps scientists avoid most issues associated with liquid-liquid extraction, enables the clean-up and concentration of analytes, and increases quantitative recovery yields.

How does SPE work?

SPE separates samples into target analytes and undesired components by taking advantage of the affinity solutes which have been dissolved in a liquid matrix have for a solid phase (also known as stationary phase). By passing the sample through a solid phase, researchers can retain either the undesired contaminants or the analytes of interest on the stationary phase.

If the stationary phase contains the components scientists want to examine, it’s rinsed in a suitable eluent so that the analytes can be collected for assay. Alternatively, if the stationary phase has retained the impurities of the sample, it gets discarded.

How to perform SPE?

In most cases, the process of SPE can be broken down into four steps:

  1. Conditioning (or equilibrating) the cartridge with a solvent so the sorbent is wet.
  2. Percolating the solution which contains the analyte of interest through the solid phase.
  3. Depending on the type of sample, either the analyte or the undesired impurities are collected on the sorbent.
  4. The sorbent is subjected to elution so researchers can gather the analyte, or discarded along with the collected impurities.

SPE can be performed in microplates for high-throughput processing. This enables researchers to quickly and efficiently carry out multiple sample with multiple sorbents in parallel. Packed into each microplate well, a single porous plastic frit can be used as an alternative to the more popular loose-filled resins. This allows SPE to work faster and more efficiently due to the pore size and improved flow characteristics.

What is SPE used for?

SPE is commonly used to improve the quality of testing by separating different sample components so scientists can focus on individual analytes without any interferences. This sample preparation technique is great for extracting specific elements from a wide range of samples, including biological fluids (such as blood, plasma, urine or saliva), natural samples (such as soil, water or air), food products (such as meat or grains) and more.

There are a number of things SPE is used for by researchers and labs, but the three main applications are:

Switching solvents – using SPE also allows researchers to turn an aqueous base sample into a volatile organic base, which they can then inject on a GC instrument.

Sample clean-up – SPE is primarily used as a sample preparation technique which allows scientists to improve their downstream analysis and chromatography by first cleaning up their samples. An added benefit of sample clean-up is the fact that it keeps instruments free of contaminants, reducing the need for system maintenance.

Sample concentration – an alternative way to use SPE is for creating concentrated samples. This is particularly handy when working with materials which have low detection or quantitation levels, and helps extend the life of older lab equipment.

Why use SPE?

Over the course of the past 40 years since the SPE method was discovered, it has grown in popularity to become one of the most powerful sample preparation tools used by the science community.  The efficiency with which SPE separates sample elements of interest from matrix interferences means the accuracy and sensitivity of assays is dramatically increased, leading to far superior qualitative and quantitative analysis.

Nowadays there are a number of phases available for SPE, most of which are based on the hydrophobic, polar or ionic properties of the samples. Each one offers different advantages and selectivity, depending on the target analyte and impurities which need to be separated.

Currently, the most highly selective phase option in the field uses Molecularly Imprinted Polymers to minimise interferents through elution and obtain optimal recoveries during chromatography analysis at any level required.

SPE vs liquid-liquid extraction

Compared to other sample preparation techniques, the SPE method offers a number of advantages, including greater high throughput amenability, specificity and reproducibility. It also has the added benefit of keeping chromatographic systems fully functioning for longer by preventing the collection of impurities on lab tools.

Unlike liquid-liquid extraction, whose targeting capabilities only extend to classes of compounds, SPE allows scientists to prepare cleaner samplers and target specific analytes of the matrix that are of interest to them.

Another big advantage of the SPE method is the batch processing capabilities it offers. From 96-well plates to vacuum manifold cartridges, the ability of this preparation technique to process batches of samples enables workflow automation.

SPE applications

Starting with cleaner samples is essential for achieving better results in any assay. Designed with this in mind, the SPE method enables scientists to rapidly purify and prepare samples ahead of conducting a chromatographic analysis. In fact, SPE is considered a crucial step in the process of sample preparation in a number of analytical labs worldwide.

SPE vs solid phase microextraction

An innovative SPE technique, Solid Phase Microextraction (SPME) can extract both volatile and non-volatile analytes from a range of liquid or solid media using a fibre coated with an extracting phase. Although how much analyte is extracted will depend on its original concentration in the sample, using the fibre is guaranteed to help reach equilibrium.

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