An Introduction of SPE and Method for Selecting SPE Cartridge
SPE is an effective method for sample purification and enrichment before analysis and determination. Compared with LLE (liquid-liquid extraction), it has the characteristics of less organic solvent consumption, convenience, safety, low cost, high analyte recovery, and good reproducibility of analysis results, which are widely used in food, medicine, environmental protection, disease control, and hygiene, commodity inspection, and pesticide residue analysis.
SPE can reduce sample preparation time and improve the accuracy and reproducibility of analysis results. SPE can greatly reduce the types and quantities of potential interferences in complex matrices such as food, environmental samples, and biological samples, and improve the accuracy of analysis and qualitative and quantitative analysis. In chromatographic analysis, the purification of samples can also extend the life of the column. The enrichment and concentration of target analytes by SPE preparation can greatly improve the detection sensitivity of the analytical method, making some important trace analyses possible.
SPE basic methods
SPE is essentially a kind of liquid chromatography separation, and the adsorbent used is the same as that of the liquid chromatography stationary phase, except that the particle size is different. The general method of SPE is: to use the principle of chromatographic analysis of selective adsorption and selective elution, pass the liquid sample through the adsorbent, retain the analytes in it, wash the impurities with a suitable solvent, and then elute the analytes with a small amount of solvent, to achieve the purpose of rapid separation purification and concentration. There is also a method of selectively adsorbing interfering impurities and allowing the analyte to be washed away, or adsorbing the impurities and the analyte simultaneously, and selectively eluting the analyte using a suitable solvent.
Method for selecting SPE cartridge
The capacity of the SPE cartridge refers to the adsorption amount of the column packing. For silica solid-phase extraction cartridges, 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 a 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: the 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, and 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, and organic compounds from non-polar substrates. Chlorine residues, etc.; graphitized carbon black (CARB) extraction columns, with graphitized carbon black as a packing, have 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.
