Different Types of SPE Cartridges
(1) SPE cartridges
SPE cartridges are commonly used. From the outside of the solid phase extraction cartridges, the classic solid phase extraction cartridges are similar to the syringe barrel and are straight. Another type of solid phase extraction cartridges has a funnel-shaped upper end, which is convenient for loading more samples at one time during manual operation.
A simple SPE cartridge is a small glass column with a diameter of a few millimeters or cartridges made of plastics such as polyintraene, polyethylene, polytetrafluoroethylene, or stainless steel. There is a sintered sieve plate with a pore size of 20μm at the lower end of the cartridges to support the adsorbent.
You can also use glass wool to replace the sieve plate, which can support the solid adsorbent and allow the liquid to flow through. Fill the sieve plate with an amount of adsorbent, and then add another sieve plate on the adsorbent to prevent the cartridge bed from being destroyed when the sample is added.
Based on the consideration of purity, medical polypropylene without additives and containing trace impurities is generally used as the material of the cartridge to avoid contamination of the sample during the extraction process. In order to reduce the impurities in the SPE blank, glass or pure PTFE can be selected as the material of the cartridge.
Sieve plate material is another possible source of impurities, the materials for making sieve plate are polypropylene, pure PTFE, stainless steel, and titanium. The metal sieve plate does not contain organic impurities but is susceptible to acid corrosion. As impurities may be introduced into the sample from the cartridges, sieve plate, and packing, a blank extraction experiment should be done when establishing and verifying the SPE method.
(2) Non-sieve plate SPE cartridges
It is a new type of integrated SPE cartridges. This product carries out special treatment on bonded silica fillers such as C18 and C8 to make them have higher mechanical strength and toughness, without adding polyethylene porous baffle as support in the cartridges. It is the first integrated SPE cartridges in the market.
(3) SPE disk
Another form of SPE cartridge is the SPE disc. The surface is similar to the membrane filter. The disc extractor is a pure polytetrafluoroethylene disc containing filler or a solid glass fiber sheet that does not need to support the filler. The filler accounts for about 60%~90% of the total amount of the SPE disk, and the thickness of the disk is about 1mm. The main difference between the SPE cartridges and disk extractor is the ratio of bed thickness to diameter. For the packing of equal weight, the load area of disk extraction is higher than that of cartridges type. The extraction is 10 times larger, thus allowing the liquid sample to flow through at a higher flow rate.
(4) Solid phase microextraction
In 1990, Pawliszyn, University of Waterloo, Canada, developed a new solid phase microextraction (SPME) separation technology based on solid phase extraction. The American Supelco company launched a commercial SPME device in 1993, which aroused repercussions in the field of analytical chemistry. The SPME device is shaped like a micro-injector, consisting of a handle and an extraction head or fiber head. The handle is used to install or fix the extraction head.
SPME device can be used forever: the extraction head is 1cm long, coated with different adsorbents, and connected to stainless steel. The molten fiber on the silk, the thin stainless steel tube is jacketed (to protect the quartz fiber from being broken), the fiber head can be expanded and contracted in the steel tube, and the thin stainless steel tube can penetrate rubber or plastic gaskets for sampling or injection. The extraction head is usually stored in the extraction head sheath.
When in use, the extraction head is immersed in the liquid or on the liquid to extract certain compounds in the concentrated sample, and then directly enter the vaporization chamber of the gas chromatograph without any solvent elution. After the extract is desorbed in the vaporization chamber, it is removed by the mobile phase. Import the chromatographic cartridges to complete the entire process of extraction, separation, and concentration.
The key to SPME is to choose the coating (adsorbent) on the quartz fiber so that the target can be adsorbed on the coating without interfering compounds and solvents. Generally speaking, non-polar coatings should be selected for non-polar targets. Layer, polar coating should be selected for the polar target.