Some SPE cartridges use reverse phase (nonpolar) silica gel as the matrix and the reverse filler is some kind of nonpolar adsorbent that extracts the nonpolar chemical compounds from the polar matrix. As for the reverse phase adsorbent, its extraction ability will go down when the non-polarity of the eluent increases.
In specific, the C18 SPE Cartridge is the bonding silica gel adsorbent with the strongest hydrophobicity. Because it has extremely strong extraction power to the nonpolar chemical compound, it is widely applied as the solid phase extraction adsorbent. Moreover, the C18 SPE Cartridge is normally considered as having the widest range of extraction among all kinds of bonding silica gel adsorbent, because it can extract most of the organic matters in the liquid matrix. When analyzing micro molecule and medium molecule, the C18 SPE Cartridge can be applied for removing salt in the liquid matrix before the ion exchange, because salt can go through the adsorbent without any reservation.
In addition, the C18 SPE Cartridge does not resist macromolecule, so it is also suitable for the desalination of protein. On the whole, the C18 SPE Cartridge can effectively separate protein, polypeptide or nucleotide in the laboratory.
Sample Treatment Process Sample treatment is the most commonly used step in C18 SPE cartridge analysis. C18 cartridge can reduce the sample processing time and can be used as follows: 1. purification: the packing in the solid phase cartridge will adsorb the compounds or the impurities in the sample. Thus, when the sample flows out, the selected compound is left on the cartridge. 2. Micro-extraction or concentration: when the amount of analytical material is below the limit of the method, the analyte can be concentrated. 3. Separation: gradient eluting, extracting the sample and increasing the sample concentration. 4. Dissolution exchange: if the sample is insoluble, the appropriate solvent can be used to adsorb and wash the analytical substance.
Factors for Affecting Separation The sample separation effect is related to the flow rate and upload. The sample size of the SPE cartridge depends on the sample structure, the volume of the solution, the polarity of the solvent, and the adsorption performance of the sample. Moreover, if the flow rate of the sample is too fast, the effective component may not remain in the adsorbent, so the flow rate is important in the activation process of the SPE cartridge.
Operative Step for C18 SPE Cartridge Here are five steps for C18 SPE cartridge use, each different but not necessary. Step 1: prepare the sample-the sample can be either a liquid phase or a gas phase. If it is a solid phase, the sample must be dissolved or extracted before the column. Step 2: activation or equilibrium of the column-activation is necessary for reversed phase columns such as C18. Use strong solvent to moisturize the stationary phase of the column, and then use a weak solvent to balance and activate the column. Step 3: sample-load the sample into the extraction column, at which point the packing in the solid phase extraction column will adsorb the compounds of interest in the sample or impurities in the sample. Thus, when the sample flows out, the selected compound (including impurities) is left on the extraction column. Step 4: rinse impurities with a washing solution that is strong enough to elute impurities and is weak enough to retain compounds of interest. Step 5: elute interested compounds-elute the compounds adsorbed on the extraction column in solution with a solvent.