Solid Phase Extraction (SPE) - Selection of the sorbent

Solid phase extraction (SPE) is an integral part of modern laboratories. It is a method for sample preparation to prepare the analyte for possible enrichment, concentration or isolation. The analytes are thereby directed and isolated by selective interactions at a solid phase, the so-called sorbent.

This type of sample preparation comes with some advantages:

• Optimization of the analysis through increased robustness for reproducible, exact test results
• Maximization of the detection selectivity to reduce ion-suppression and protein binding and for better compatibility of the solvent with the analysis method
• Improving the performance of the analytical system for a longer column life and less contamination of the analytical system
• Hightening of the sensitivity by concentration of the analytes for more accurate quantification and lower limits of detection

These so-called matrix effects are an issue in many areas of analytical chemistry, however, modification of ionisation (ion suppression/enhancement) can be a major problem in atmospheric pressure ionisation (API), mass spectrometry and, in particular, electrospray based ion sources.

Selection of a suitable sorbent

Many different sorbents are available for the solid phase extraction. When selecting the appropriate sorbent, care must be taken that the sample solution drastically determines the type of the appropriate sorbent.

For aqueous samples, only non-polar sorbents should be used as otherwise the water molecules would occupy all the adsorption sites on the sorbent surface. Among the non-polar sorbents are, for example, C18 or polymer material.

If a user wishes to extract an analyte from non-polar solutions, such as hexane or dichloromethane, polar sorbents such as, for example, silica gel, diol, aminopropyl or cyanopropyl are most suitable.

For ionic substances, users can use an ion exchanger to enrich the analyte.

If you want to obtain further information about the SPE phases, please take a look here.