Some professional terms are usually involved in solid phase extraction technology. Here are some common terms and their corresponding explanations.

Void volume
For SPE adsorbent with a certain mass filled in SPE column, the volume of solvent filled with adsorbent particles and inner pore space is equal to the volume of column bed. For 40 μ m. 60 μ m adsorbent, the column bed volume is about 120 μ L / 100mg adsorbent.

Column breakthrough
The target compound was not retained by SPE adsorbent during sample loading, but flowed through SPE column. Column penetration occurs when the retention of the target compound in the adsorbent is too weak or the adsorbed sample exceeds the column capacity.

Column capacity
In a certain solution environment, a given SPE column can retain the total amount of target compounds and interferents. For a target compound, the column capacity of the adsorbent is related to the solution matrix. Generally, the column capacity will not be greater than 5% of the mass of adsorbent.

Column volume
Common SPE columns are 1ml, 3ml, 6ml, etc. The ML here refers to the volume of SPE empty column. The column volume is not equal to the sample volume that can be loaded into an SPE column. For example, the sample load of 1ml SPE column is not equal to 1ml. The sample loading of SPE column depends on the column capacity and sample concentration. Generally, the sample loading is greater than the column volume.

Column pretreatment is also called column activation. The main purpose is to make the SPE column reach the best state of extraction, so as to adsorb the target compound. For the reversed-phase SPE column based on silica gel, it must be noted that the activated SPE column must be kept wet before loading the sample.

Covalent interaction
Covalent interaction refers to the covalent bond formed between the target compound and the adsorbent. Covalent bonds are generally not easy to reverse, but they are reversible under certain conditions. Covalent interaction is not common in solid phase extraction, but it has good selectivity. For example, at low pH, boron atoms are bonded to three different atoms. When the pH rises to 8.5, the boron atom binds to the OH group. In this state, the two oxygen atoms connecting the boron atom form a covalent bond with the target compound. It can form covalent bonds with phenol, amine or diol. When the pH drops to 1.0, the target compound is released.

The purpose of drying the SPE column before eluting the target compound is to remove water from the extraction column for better elution. At the same time, it can also prevent the damage of water to the gas chromatographic column.

Elution is the process of eluting the target compound from the SPE column with an appropriate solvent. The appropriate elution solvent should be selected according to the different retention mechanism of SPE column to the target compound. The choice of solvent is to elute the target compound to the greatest extent, and the less impurities co eluted, the better.

Trimethylchlorosilane is used to react the silicon hydroxyl groups on the surface of silica gel matrix that are not bonded with functional groups, so as to reduce the number of silicon hydroxyl groups, so as to reduce the interference of silicon hydroxyl groups on the main force in solid phase extraction.

Extraction mechanism
In solid phase extraction, extraction mechanism refers to the chemical essence of the interaction between compounds and adsorbents. In solid phase extraction, the main extraction mechanisms are nonpolarity, polarity, ion exchange, covalent and so on.

Functional group
Functional groups are also called functional groups. In solid phase extraction, functional groups refer to the atomic groups of compounds with certain properties. These atomic groups can be adsorbed by the adsorbent under certain conditions, so that the target compound can be retained on the SPE column. Properly changing the conditions can destroy this interaction and release these atomic groups from the adsorbent.

Interaction refers to the attraction or repulsion between two compounds in a certain chemical environment. In solid phase extraction, there are three basic interactions: target compound / adsorbent, sample matrix / adsorbent and target compound / sample matrix.

Interferents, also known as impurities, refer to substances that have a negative effect on the extraction or detection of target compounds. There are two main types of interferences. One kind hinders or restricts the adsorption of adsorbents to target compounds by competing with or combining with target compounds; The other is the substance that interferes with the final detection. These two kinds of interferences should be removed as much as possible during sample pretreatment.

Ion exchange
Ion exchange is the interaction between ionic functional groups in compounds and functional groups with opposite charges on the surface of adsorbents. Ion exchange can be controlled by solvent pH, ionic strength, selectivity of competitive ions and other conditions. According to the interaction energy between compound and adsorbent, the ion exchange interaction can be divided into strong and weak.

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