3 Types of SPE Cartridges: Silica Gel, High Polymer, and Inorganic Material

Solid phase extraction(SPE) is the separation principle of liquid chromatography using selective adsorption and selective elution. The more commonly used method is to pass the liquid sample solution through the adsorbent to retain the test substance, then use a solvent of appropriate strength to wash away impurities, and then use a small amount of good solvent to quickly elute the test substance, so as to achieve the purpose of rapid separation, purification, and concentration. Also, it is able to selectively absorb interfering impurities and make the measured material flow out. Or absorb impurities and the tested substance at the same time, and then use an appropriate solvent to selectively elute the tested substance.

On the market, there are various types of SPE cartridges. In the specific experimental work, it is necessary to select appropriate packing and reasonable specifications of SPE columns according to the analysis object, detection method, and laboratory conditions. Consider the extraction capacity of the SPE column for the analytical object, the volume of the sample solution, the final volume of the solution after elution, and the total amount of analytes and interferences in the sample solution.

In addition to the required specifications, the key to selecting an SPE cartridge is its packing material which determines the separation performance. When choosing an extraction column, you must choose a suitable packing according to the type of sample to be tested and its physical and chemical properties. The packings are usually chromatographic adsorbents, which can be roughly divided into three categories, which are based on silica gel, polymers, and inorganic materials.

Solid-phase extraction(SPE) has the same fundamental basis as HPLC. When you have knowledge of the chromatographic behavior of the analytes of interest, you can choose the proper sorbent and eluents. That means if you know that certain chromatographic conditions can provide good separation of your analyte from interference, a similar SPE sorbent and solvent combination might be your choice. If you try to remove interference with solutes in HPLC, you will find out that similar SPE conditions won’t work very well.

Generally, there are two ways to isolate and clean up sample components of interest: one is to adsorb matrix interference as components of interest pass through the cartridge unretained, and the other one is to adsorb components of interest, and the matrix interference passes through the cartridge without any retaining at the same time. You can choose the first way when the desired sample component is present in high concentration. And the second way can be the choice When you find the components of interest are presenting at low levels, or when you need to isolate the multiple components of different polarities.

Fillers used for SPE cartridges are usually chromatographic adsorbents, which can be divided into three kinds: the first is based on silica gel such as C18、C8, etc.; the second is based on polymers such as polystyrene-divinylbenzene, etc.; and the third is based on inorganic materials such as verori diatomite, alumina, graphitic carbon, etc. different kinds of fillers can meet different needs of your applications.

Silica gel of SPE cartridge

The first type is based on silica gel, such as C18 solid phase extraction cartridge. Being polar and weakly acidic, the silica gel can be used in two separation modes: normal phase or reverse phase. The performance is weaker than silica gel, and the non-polarity is weaker than C18 or C8 in reverse extraction.

Most of the SPE cartridges are silica gel type made of polyethylene, which contains two pieces of plug made of polypropylene or glass fiber, and a certain amount of chromatographic adsorbent is filled in the middle of the two pieces. The upper end of the solid phase extraction column is open, the lower end is the outlet, and the liquid is discharged from the outlet after passing through the adsorbent. According to the space volume above the packing of the classical solid phase extraction column, the specification of the solid phase extraction column can be divided into 3mL、6mL、12mL, and so on.

With a good extraction effect on steroids, usually, it is used to extract non-polar or weak polar compounds or to remove polar impurities. It is mainly used in blood samples, urine samples, drugs and their metabolites, polypeptide desalination, trace organic compound enrichment in environmental samples, and organic acids in beverages.

Polymers of SPE cartridge

Secondly, it is based on polymers, taking polystyrene-divinylbenzene for example. The extraction cartridge packed with high-purity, high-crosslinking styrene-divinylbenzene polymer as a stationary phase has a high sample load, can withstand extreme pH conditions and different solvents, and has excellent resistance to polar compounds retention capacity.

It can be used as a general-purpose adsorbent for acidic, neutral, and basic compounds usually used to retain hydrophobic compounds containing hydrophilic groups under reversed conditions, such as phenols, nitroaromatics, nitroamines, nitrates, etc.

There are also SPE cartridges of special specifications produced according to multiple quality sorbent choices. The polymer-type SPE cartridge is a universal sorbent that can meet all different SPE-needed occasions. From the appearance of the solid phase extraction column, the polymer and adsorption type extraction column is similar to the injection syringe and is straight cylinder type, which is convenient to load more samples at one time during manual operation.

Inorganic materials of SPE cartridge

Thirdly, it is based on inorganic materials, for example, graphitized carbon, alumina, Flory diatomaceous earth, and so on. Florisil is a kind of polar silica gel adsorbent composited with magnesium oxide. The matrix-based extraction cartridge is suitable for absorbing polar compounds such as POLYchlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and organochlorine residues from non-polar matrices.

Graphitized carbon black (CARB) extraction cartridge, with graphitized carbon black as the filler, the extraction process is very rapid, and the adsorption capacity for compounds is more than double that of silica gel. It has a strong affinity for planar molecules and is very suitable for the extraction and purification of many organic materials, especially for the separation, thanks to the regular six-member ring structure on the surface of graphitized carbon black.

Or remove various substrates such as pigments, sterols, phenols, and other substances in fruits and vegetables; fillers based on alumina include acid, alkali, and neutral types, which are suitable for separation and extraction of acidic, alkaline, and neutral solvents.

Constituent Elements of SPE Cartridge

SPE cartridge is composed of a medical PP empty tube, a medical PE sieve plate, and a fixed adsorbent. The PE-made tube has high chemical compatibility and wonderful reproducibility. Medical PE sieve plate has average pore size and good flow rate. It can be used to retain or elution of polar and halogenated compounds in a pollution-free way.