The solid phase extraction is a laboratory application for sample preparation. The method involves more or less six different steps (based on ThermoFisher 2012). The analyte is dissolved in a solvent, but not in abundance. The SPE is used to further enrich the substance to be analyzed, which has been diluted in said solvent, in order to be able to use it later for other analyzes.
In order to achieve the best possible reproducible end result, the sample should be adapted in advance to the respective analysis parameters. Firstly, it is important to determine the concentration of the analyte in the sample as well as the matrix complexity and the sample quantity. Then the sample or composition of the matrix should be adapted for the correct ionic strength and dilution. Furthermore, it is advisable to test the sample for impurities or additional substances and, if necessary, to remove them by filtration.
1. Conditioning of the sorbent
This step serves to make the sorbents used more susceptible to the analyte and ensure reproducible flow. It is extremely important that a suitable sorbent for the column and the final analysis is used to ensure correct results.
2. Application of the sample
Care should be taken to ensure that the sample is applied to the sorbent at an appropriate flow rate - a rate of 1 ml per minute is usually applied. Subsequently, depending on the SPE phase, different results arise. Please take a look at this SPE phase overview.
In this step any impurities or unwanted residues, which are only weakly bound, should be removed. Thus only the much more strongly bound, desired compositions remain. To remove the separated substances, it is advisable to use a very strong solvent for the cleaning process, but still weakly enough so that it does not destroy the desired ingredients.
4. Elution of the analytes
Finally the analytes are washed out with the aid of various solvents for the last time. A smaller amount of elution produces a more concentrated substance. In particular, the washing and rinsing process should be carried out with the utmost precision and, as far as possible, optimized in order to provide the best, reproducible test results.