As we know, the quality of the packing in the SPE cartridge affects its adsorption capacity. The adsorption capacity refers to the total mass of compounds (including target compounds and some interfering substances) that a certain mass of adsorbent can retain under certain conditions.
Common specifications of adsorption capacity
Silica gel matrix: the cartridge capacity does not exceed 5% of the mass of the SPE packing material. For example, a 100 mg/1 ml C18 cartridge can retain 5 mg of the compound.
Polymer matrix: The cartridge capacity is 3 times that of the silica-based adsorbent. For example, a 100 mg/1ml BRP cartridge can retain 15 mg of the compound.
Ion exchange adsorbent: the exchange capacity is 0.25-1mmol/g, 1mmol/g means that 1g adsorbent can adsorb 1mmol of monovalent charged substances.
Therefore, in solid phase extraction, it is very important to select the appropriate cartridge specifications according to the sample load. When the sample load exceeds the adsorption capacity of the adsorbent packing, the target compound will no longer be retained by the adsorbent but will flow out of the SPE cartridge with the sample matrix, resulting in a decrease in recovery rate.
Balancing The Extraction Speed And Sample Capacity
Solid phase extraction (SPE) is a rapid, effective, economical path to remove interfering compounds, concentrate or extract the analyte in a preferred solvent.
On one hand, SPE and chromatography base on the same principles: SPE uses the HPLC column solid phase packing with materials in a single-use container, and the scientists can choose different stationary phases just like HPLC columns; but on the other hand, SPE is different from HPLC, performing as a low resolution and very low-pressure method which is designed for samples preparation by removing interfering substances or concentrating a sample.
SPE cartridge, which are single-use plastic tubes Is the key part of the SPE technique. Before you choose the SPE cartridge, there is something you should know. First, the cartridge volume should match the wash solvent volume including the volume of the sample and solvent added. The sample can be loaded is 5-10% of the sorbent weight in a given SPE cartridge.
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