- 6 September 2006 -

Anachem's new web solution targets SPE method development

Chromatography specialist Anachem Limited's Patrick Boyce describes the company's web-based SPE method tool for faster solid phase extraction method development - www.SPEnet.co.uk.

Traditional liquid-liquid extraction procedures employ a serial extraction of an aqueous sample with an organic solvent, resulting in a relatively large volume of solvent that must be dried and concentrated prior to analysis. However, these methods are being increasingly replaced by Solid Phase Extraction (SPE) techniques for the determination of organic analytes in aqueous samples. SPE is used most often to prepare liquid samples and extract semi-volatile or non-volatile analytes, but is also applicable to solids that are pre-extracted into solvents.

SPE - how does it work?
Solid-phase extraction uses a solid phase and a liquid phase to isolate one, or one type, of analyte from a solution. It is usually used to clean up a sample before using a chromatographic or other analytical method to quantitate the amount of analyte(s) in the sample. The general procedure is to load a solution onto the SPE phase, wash away undesired components, and then wash off the desired analytes with another solvent into a collection tube.

A solid sorbent material, typically an alkyl bonded silica, is packed into a cartridge or embedded in a disk and performs the same function as the organic solvent in liquid-liquid extraction. For example, reverse-phase SPE employed to extract non-polar compounds from polar samples such as water (pesticides for example) generally uses a solid sorbent containing non-polar functional groups such as octadecyl (C18) or octyl (C8) bonded silicas. Aqueous samples are pumped or pulled through a cartridge or disk and the organic compounds in the samples interact with non-polar functional groups on the sorbent and are effectively extracted from the sample. Organic compounds in the original aqueous sample are eluted from the cartridge or disk with a small volume of organic solvent.

SPE - advantages of use
Compared to the classic liquid-liquid extraction using a separatory funnel, SPE offers several advantages. Practically it is much more convenient with easier manipulations; samples can be processed quickly, reducing laboratory time; there is less of a requirement for the use of expensive, breakable specialty glassware; solvent usage is greatly reduced, decreasing exposure of analysts to these hazardous chemicals and eliminating the problematic disposal of large quantities of organic solvents; SPE is also much easier to automate; and reaction mixtures from parallel synthesis can easily be purified in a parallel fashion with commercially available disposable cartridges/tubes/disks and a vacuum manifold.

SPE also has analytical advantages. It is more efficient than liquid/liquid extraction and yields quantitative extractions; organic analytes can be isolated from large volumes of water with minimal or no evaporation losses; higher concentration factors can be achieved and there are no problems with the miscibility of solvents; SPE avoids problems such as incomplete phase separations, less-than-quantitative recoveries and emulsion formation, as encountered in liquid-liquid extractions; and the process is also easily adaptable for very selective extractions, and can provide more reproducible results.

Developing the best method
A wide range of SPE products are accessible that are excellent for sample extraction, concentration, and cleanup. They are available in a wide variety of chemistries, adsorbents, and sizes, but, selecting the most suitable product for each application and sample is important.

Scientists can spend much of their research time trying to develop efficient SPE methods for extracting their particular analyte of interest and removing specific contaminants from a variety of samples.

Whilst the actual SPE procedure is easy to perform, developing the best method is more difficult. A basic knowledge in selecting the right sorbent (from a variety of reversed, normal or ion exchange phases), conditioning, selective washing and eluting the compounds of interest, is necessary to obtain the most efficient extractions. Selecting the appropriate SPE chemistry and conditions takes considerable knowledge and experience, and researchers can get frustrated spending time and wasting reagents to develop the perfect solid phase extraction protocol.

Anachem, however, has come up with a short cut to help laboratories prepare, purify and concentrate their target compounds in the shortest amount of time, with considerable versatility. A specific software programme has been built that provides individual protocols to guide users to the most suitable method for their particular sample preparation requirements.

Using the online product
To develop any SPE method, three critical groups of information are required. These include the sample matrix (blood, urine, water etc), the structures of all compounds to be extracted and finally, all the structures of the interferences to be eliminated. The tool allows users to input all these details, including an unlimited number of compounds to extract, and interferences to eliminate.

SPEnet suggested methods are best starting points for the extraction to be performed, and are based on Anachem's SPEnet range of solid phase extraction cartridges.