The Role of SPE Cartridge and Preparation Before Operating SPE Instrument

The solid phase extraction cartridge is a sample pretreatment method based on chromatographic separation, and it is a popular and mature sample pretreatment method in recent years. There are solid phase and liquid phase and it can adsorb and retain specific compounds on the extraction column, as the SPE adsorbents have different functional groups.

1. The role of solid phase extraction cartridge
1.1 Separation
The target is separated from a large amount of sample matrix, and the sample matrix is removed, and at the same time, the sample is converted into a form acceptable to the instrument before the instrument analysis can be performed. SPE is not only suitable for the separation of target compounds and matrix removal in small-volume samples, but also for the enrichment of trace target compounds in large-volume samples.

1.2 Purification
One of the main purposes of sample pretreatment is to remove components or impurities in the sample that interfere with the instrument or analysis.

1.3 Solvent switch
There is no emulsification problem in SPE, and there is no direct interaction between organic solvent and water phase.

There are currently two main methods for online combination of SPE cartridge:
One is to use a switching valve to connect the extraction cartridge and the chromatographic analysis column, and let the chromatographic mobile phase transfer all the samples enriched on the extraction cartridge to the chromatographic analysis column (direct method).

The other is the indirect method, which uses the same purification method as offline solid phase extraction. After the sample components are collected, use the built-in sampler of the extractor to take 10-20 microliters of components and inject them into the chromatographic analysis column.

Ion-Exchanger SPE Cartridge SAX SPE Cartridges

2. Types
There are many types of solid phase extraction cartridges. In the specific experimental work, it is necessary to reasonably select suitable packing and reasonable specifications of solid phase extraction cartridge according to the analytical objects, detection methods, and laboratory conditions.

Consider the extraction capacity of the solid phase extraction cartridge for the analytical object, the volume of the sample solution, the final volume of the solution after elution, and the analytes and interferences’ total amount in the sample solution. At present, it is mainly used in the field of food safety, such as the analysis of the residues of various antibiotics and antibacterial drugs in various foods; the analysis of pesticide residues in agricultural products; the analysis of legal and illegal additives in various foods.

In the field of drug research, it is widely used in drug pharmacokinetics, pharmacokinetic analysis, and traditional Chinese medicine analysis. In the field of environmental protection, solid phase extraction cartridges are used in the analysis of polycyclic aromatic hydrocarbons (PAHs) , PCBs, and various pesticides in the environment; and the analysis of organic substances in drinking water, groundwater, and sewage.

Common solid phase extraction cartridge are mostly injection syringe-type devices made of polyethylene. The device is equipped with two plugs made of polypropylene or glass fiber, and a certain amount of chromatographic adsorbent is filled between the two plugs ( filler). The SPE cartridge’s upper end is open and the lower end is a liquid outlet, by which the liquid is discharged.

According to the volume of space above the packing of classic solid phase extraction columns, the specifications can be divided into 60ml, 30ml, 20ml, 15ml, 10ml, 6ml, 3ml, and 1ml. There are also special SPE cartridges produced according to specific application requirements. From the appearance of the solid phase extraction column, the classic solid phase extraction column is similar to the syringe and is straight.

3. Preparations
The preparations for the solid phase extraction instrument before use are as follows:
3.1 column pretreatment
Before use, the SPE cartridge needs to be pretreated with a suitable solvent so as to remove the possible impurities in the packing. By doing so, it is to achieve good reproducibility and a high recovery rate. Another purpose is to solvate the packing and increase reproducibility.

3.2 the addition of samples
After pretreatment, the sample solution is added to and passed through the column at a certain flow rate. In this step, the analyte is retained on the adsorbent.

3.3 Washing of the column
When the sample passes through the extraction column, not only the analyte is adsorbed on the column, but also some impurities are also adsorbed at the same time. Choose an appropriate solvent to elute the interfering components while keeping the analyte on the column.

3.4 Elution of analyte
Use an eluent to elute the analyte in the collection tube. In order to increase the concentration of the analyte or adjust solvent impurities for later analysis, the collected analyte can be integrated and dried with nitrogen, and then dissolved in a small volume of an appropriate solvent.