The capacity of the SPE cartridge refers to the adsorption amount of the column packing. For silica-based solid-phase extraction columns, the capacity is generally 1 to 5 mg/100 mg, which means that the column capacity is 1% to 5% of the mass of the packing. The capacity of the bonded silica gel ion exchange adsorbent packing is expressed in meq/g, that is, the capacity per gram of filler is X milligram equivalent. The capacity of this kind of packing is usually 0.5 ~ 1.5 meq / g.
There are many types of SPE cartridges. It is necessary to reasonably select SPE cartridges with suitable packing and reasonable specifications according to the analysis object, detection method, and laboratory conditions. The extraction capacity of the SPE column for the analysis object, the volume of the sample solution, the final volume of the eluted solution, and the total amount of the analyte and interference in the sample solution should be considered. Generally, the total mass of the test object and the interfering substance adsorbed by the adsorbent in the column should not exceed 5% of the total mass of the adsorbent. The volume of the eluent should generally be 2-5 times the volume of the bed of the extraction column.
How to choose an SPE cartridge?
SPE cartridge is a sample pretreatment device developed from chromatography column for extraction, separation, and concentration. Most common SPE cartridges are injection syringe-type devices made of polyethylene. There are two plugs made of polypropylene or glass fiber in the device. The two plugs are filled with a certain amount of chromatographic adsorbent (packing). The SPE cartridge is packed with a high-purity spherical adsorbent, which is more uniformly distributed, ensuring the repeatability and consistency of the experimental results, in order to ensure a safe, reliable and sample preparation process.
In addition to the required specifications, the key to selecting an SPE cartridge is its packing. When selecting an extraction column, you must choose the appropriate packing according to the type of sample to be tested and its physical and chemical properties. Solid-phase extraction packings are usually chromatographic sorbents and can be roughly divided into three categories, which are based on silica gel, polymers, and inorganic materials.
The first type is based on silica gel, such as C18 solid-phase extraction cartridges. Silica gel is very polar and weakly acidic. It can be used in two phases: normal-phase or reversed-phase. The polarity is weaker than silica gel, and the non-polarity is weaker than C18 or C8 during reversed-phase extraction. It has a good extraction effect for steroids. It is usually used for the extraction of non-polar or weakly polar compounds or the removal of polar impurities, which is mainly used for blood and urine samples and their metabolites, peptide desalination, enrichment of trace organic compounds in environmental samples, organic acids in beverages.
The second type is based on polymers, such as polystyrene-divinylbenzene. Styrene-divinylbenzene polymer featuring high-purity and crosslinking can withstand extreme pH conditions and different solvents, with excellent properties for polar compounds retention ability It can be used as a general-purpose adsorbent for acidic, neutral and basic compounds. It is usually used to retain hydrophobic compounds containing hydrophilic groups under reversed-phase conditions such as phenols, nitroaromatics, nitramines, nitrates Class, etc.
The third type is based on inorganic materials, such as Flori diatomite, alumina, and graphitized carbon. Florisilite is a kind of polar silica gel adsorbent compounded with magnesia. The extraction column based on it is suitable for adsorbing polar compounds such as polychlorinated biphenyls, polycyclic aromatic hydrocarbons, organic compounds from non-polar substrates. Chlorine residues, etc.; graphitized carbon black (CARB) extraction columns, with graphitized carbon black as a packing, has a very fast extraction process. The adsorption capacity of the compound is more than double that of silica gel. Due to the regular six-membered ring structure on the surface of graphitized carbon black, it has a strong affinity for planar molecules, which is very suitable for the extraction and purification of many organic substances, especially for separation or re-movement of various substrates such as pigments, sterols, phenols in fruits and vegetables; alumina-based fillers have three types of acid, alkali and neutral, which are suitable for the separation and extraction of acid, alkaline and neutral solvents.
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