The following points should be considered when selecting the separation mode and adsorbent for solid phase extraction.
The solubility of the target compound is polar or non-polar solvents mainly involves the choice of the eluent. Whether the target compound is possible to ionize (the pH value can be adjusted to achieve ionization), so as to decide whether to use ion exchange solid phase extraction cartridge.
Is it possible for the target compound to form a covalent bond with the adsorbent, such as forming a covalent bond, you may encounter trouble during elution. The degree of competition between non-target compounds and target compounds on the adsorption point of the adsorbent is related to whether the target compounds and interfering compounds can be separated well.
Commonly used adsorbents (stationary phase) for solid phase extraction
Since solid phase extraction is essentially a liquid chromatography separation, in principle, all materials that can be used as liquid chromatography cartridge packing can be used for solid phase extraction cartridge.
However, because the cartridge pressure of liquid chromatography can be higher and the column efficiency is required to be higher, the particle size requirements of its packing are strict. In the past, 10μm particle size packing was commonly used, and now high-efficiency cartridges use 5μm packing, even 3μm packing (As the HPLC pump pressure increases, the particle size of the filler is gradually decreasing). The requirements for the particle size distribution of the filler are also very narrow. The pressure on the solid phase extraction cartridge is generally not large.
The purpose of separation is only to separate the target compound from the interfering compound and the matrix. The column efficiency requirements are generally not high.
Therefore, the fillers used as solid phase extraction adsorbents are relatively coarse. 40μm can be used, and the particle size distribution requirements are not strict, which can greatly reduce the cost of the solid phase extraction cartridge. Types and uses of adsorbents commonly used in solid phase extraction.
Solid phase extraction equipment and operating procedures
The simplest solid phase extraction device is a small cartridge with a diameter of several millimeters. The small cartridge can be glass, polypropylene, polyethylene, polytetrafluoroethylene, and other plastics, or stainless steel. There is a sintered sieve plate with a pore size of 20μm at the lower end of the small cartridge to support the adsorbent. If the self-made solid phase extraction cartridge does not have a suitable sintered sieve plate, it can also be filled with glass wool instead of the sieve plate, which can support the solid adsorbent and allow the liquid to flow through.
Fill the sieve plate with a certain amount of adsorbent (100㎎~1000㎎, depending on the need), and then add a sieve plate on the adsorbent to prevent damage to the column bed when adding samples (it is also possible if there is no sieve plate Replace with glass wool). At present, solid phase extraction cartridges of various specifications and loaded with various adsorbents have been sold, which is very convenient to use.