About the Role of SPE Cartridge in the SPE Process

Solid phase extraction (SPE) is the use of a solid adsorbent to adsorb a target compound in a liquid sample, separating it from the matrix and interfering compound of the sample, and then eluting with an eluent or desorbing it to achieve the purpose of separating and enriching the target compound.

Compared with the traditional liquid-liquid extraction method, the recovery rate of the analyte can be improved, the analyte can be separated from the interference component more effectively, and the sample pretreatment process can be reduced, which is easy to operate, time-saving and labor-saving.

SPE cartridge

SPE cartridge, also called SPE cartridge is a sample pretreatment device for extraction, separation and concentration developed from a chromatography column. It is mainly used for sample pretreatment of various foods, agricultural and livestock products, environmental samples and target compounds in biological samples.

The capacity of the SPE cartridge refers to the adsorption amount of the cartridge packing. For silica-based SPE cartridges, the capacity is generally 1~5 mg/100 mg. The capacity of the bonded silica ion exchange adsorbent packing is expressed in meq/g. The capacity of such packing is usually between 0.5 and 1.5 meq/g.

SPE device

The SPE device consists of an SPE cartridge and accessories. The SPE cartridge consists of three parts, a column tube, a sintered pad and a packing . SPE accessories generally include vacuum systems, vacuum pumps, blow dryers, inert gas sources, large capacity samplers, and buffer bottles.

SPE process

The SPE process requires the sample to be in solution, without interference, and with sufficient concentration to be detected. The SPE process can be described as the following five steps:

Step 1: select the extraction tube.
1. Normal phase, reverse phase and adsorption column: The sample quality does not exceed 5% of the mass of the filler.
2. LC-NH2 and LC-WCX columns: The ion exchange capacity is determined by the application.

Step 2: extraction tube pretreatment
Reverse phase silica gel and non-polar sorbent media are usually pretreated with a water soluble organic solvent such as methanol. Normal phase SPE silica gel and polar adsorbent media are usually pretreated with the organic solvent in which the sample is located. For Ion exchange packing, the samples in non-polar organic solvents are pre-treated with sample solvent. The sample in the polar solvent was pretreated with a water-soluble organic solvent.

Step 3: add sample
When an excess volume of the aqueous solution is extracted, the reverse phase silica gel filler gradually reduces the solvation layer obtained during the pretreatment. This will reduce the extraction efficiency and sample recovery. To avoid clogging the filter of the SPE cartridge, pre-filter or centrifuge the sample prior to extraction, if possible. The flow rate will affect the retention of certain compounds and the drop rate is best, if time permits.

Step 4: rinse the packing
If the analyte is retained on the filler, rinse off the unwanted material with a solution that does not elute the desired compound. The rinse solution does not exceed one tube volume.

Step 5: elute the compound of interest
The packing is rinsed with a small amount of solution capable of eluting the analyte, and eluting the analyte with small amounts of liquid twice is more effective than using one large volume. The reversed phase, normal phase, and ion exchange processes generally requires five steps; the sample purification process only needs the first three steps.