Do You Know There Are Several Steps in Process of Using SPE and Operation Methods of SPE Cartridges?
The solid phase extraction(SPE) device is a widely used and popular sample pretreatment technology. It uses a solid adsorbent to adsorb the target compound in the liquid sample, separate it from the sample matrix and interfering compounds, and then wash it with an eluent. It is developed based on the traditional liquid-liquid extraction based on the principle of similar intermiscibility with similar interactions between substances and combined with the basic knowledge.
4 steps for using SPE device
SPE is mainly retained/adsorbed by the force between the functional group on the solid-phase adsorbent and the functional group of the target compound. This force can be divided into non-polar force, polar force, ionic force and covalent force, etc. HAWACH discusses the four steps in the process of the SPE device.
(1) Pretreatment of SPE cartridges
Before extracting the sample, the adsorbent must undergo proper pretreatment, in order to wet and activate the SPE packing, so that the target extract is in close contact with the solid phase surface, which is prone to intermolecular interaction; the other is to remove the possible packing impurities and reduce pollution. The method adopted is to flush the extraction cartridges with a certain amount of solvent. According to SPE packing, we have Reversed Phase C18 SPE Cartridges, Ion-Exchange SCX SPE Cartridges, Ion-Exchange SAX SPE Cartridges.
Generally, the reversed-phase silica gel is pretreated with methanol. The methanol wets the surface of the adsorbe, nt and permeates the bonded alkyl phase, so that water can more effectively wet the surface of the silica gel. Then replace the methanol remaining in the column with water or a buffer solution, so that the sample aqueous solution is in good contact with the surface of the adsorbent, and the extraction efficiency is improved. Pretreat the normal-phase silica gel and polar adsorbent media with the organic solvent. Ion exchange packing generally uses 3-5ml deionized water or low-concentration ion buffer solution for pretreatment.
The SPE packing should be kept moist from pretreatment to sample addition. If the packing in the SPE cartridge is lost before the sample is added, the pretreatment process needs to be repeated. And before re-introducing the organic solvent, rinse with water to remove the salt in the buffer solution in the column.
(2) Sample loading
Pour the sample into the activated SPE cartridge, and then use pressure, vacuum, or centrifugation to make the sample enter the adsorbent. Use manual or pump to push positive pressure or negative pressure suction to make the liquid sample pass through the solid phase extraction column at an appropriate flow rate. At this time, the target extract in the sample is adsorbed on the solid phase extraction column packing.
(3) Washing interference impurities
The purpose of washing is to remove a small number of disturbed components from the matrix adsorbed on the column. Generally, a medium-strength mixed solvent is selected to remove the interfering components in the matrix as much as possible without causing the loss of the target extract. For example, a reversed-phase extraction system often uses a certain ratio of organic solvents and water mixtures, and the ratio of organic solvents should be greater than the sample solution but less than the eluent solution.
(4) Elution and collection of analytes
Choose an appropriate elution solvent to elute the analyte, collect the eluate, and evaporate the solvent for later use or directly perform online analysis. In order to elute the analyte as much as possible and keep the impurities that are stronger than the analyte adsorbed on the SPE column, it is necessary to select an elution solvent with appropriate strength.
3 methods for SPE cartridges operation
(1) Reverse phase SPE cartridges operation
Extract non-polar samples from the polar matrix
1. Activation: Take 3-5 ml methanol to rinse the column and keep it moist.
2. Sample loading: Make the sample evenly pass through the extraction column at an appropriate flow rate
3. Cleaning: Take 5 ml appropriate polarity solvent to clean the column.
4. Elution: Take 1-5 ml non-polar solvent to elute the tested sample.
(2) Normal phase SPE cartridges operation
Extract polar samples from the non-polar matrix
1. Activation: 3-5 ml of non-polar solvent to wash the extraction column.
2. Cleaning: Eluting the extraction column of the adsorbed sample with 5 ml of appropriate non-polar solvent.
3. Elution: Elute the sample to be tested with 1-5 ml of polar solvent in batches.
(3) Ion exchange SPE cartridges operation
Extract charged samples
1. Activation: rinse the extraction column with 3-5ml deionized water/or buffer with low ionic strength
2. Sample loading: at a lower flow rate, make the sample evenly pass through the extraction column
3. Cleaning: 5ml deionized water/or buffer with low ionic strength to rinse the extraction column
4. Elution: Use 1-5 ml of high ionic strength buffer to elute the sample to be tested to the collection container.