What Is a Solid Phase Extraction?

Solid-Phase Extraction (SPE) is a sample pretreatment technology developed in recent years. It is a combination of liquid-solid extraction and column liquid chromatography technology. It is mainly used for the separation, purification and concentration of samples. Compared with the traditional liquid-liquid extraction method, the recovery rate of the analyte can be improved, the analyte can be more effectively separated from the interference components, the sample pretreatment process can be reduced, and the operation is simple, time-saving and labor-saving. Widely used in medicine, food, environment, commodity inspection, chemical industry and other fields.

Solid Phase Extraction

Solid Phase Extraction (SPE) is a sample pretreatment technology developed since the mid-1980s. Developed by a combination of liquid-solid extraction and liquid chromatography. It is mainly used for the separation, purification and enrichment of samples. The main purpose is to reduce sample matrix interference and improve detection sensitivity.

SPE technology is based on the theory of liquid-solid phase chromatography. It uses selective adsorption and selective elution to enrich, separate, and purify samples. It is a physical extraction process that includes liquid and solid phases; it can also be approximated. Ground is regarded as a simple chromatographic process.

SPE is a principle of liquid chromatography separation using selective adsorption and selective elution. The more common method is to pass the liquid sample solution through the adsorbent, retain the test substance therein, and then use a suitable strength solvent to wash away impurities, and then quickly elute the test substance with a small amount of solvent to achieve the purpose of rapid separation, purification and concentration. It can also selectively adsorb interfering impurities and allow the test substance to flow out; or simultaneously adsorb the impurity and the test substance, and then use a suitable solvent to selectively elute the test substance.

The operation is slightly different depending on the packing retention mechanism (the packing retains the target compound or the impurities).

A solid-phase extraction operation typically has four steps (see Figure 1):

1. Filler retains target compound

l Activation ---- remove impurities in the small column and create a certain solvent environment.

l Loading ---- dissolve the sample with a certain solvent, transfer it to the column and keep the components on the column.

l Rinse-remove interferences to the greatest extent.

l Elution ---- Use a small volume of solvent to elute the test substance and collect it.

2. Filler retains impurities

There are generally three steps in a solid phase extraction operation (see Figure 2):

l Activation-remove impurities from the column and create a certain solvent environment.

l Loading-transfer the sample to the column, at this time most of the target compounds will flow out with the sample base solution, impurities will be retained on the column

l So this step should start collecting

l Elution --- Use a small volume of solvent to elute and collect the components, and combine the collection solutions.

This situation is mostly used to remove pigments in food or pesticide analysis.

Compared with the traditional liquid-liquid extraction and protein precipitation methods, solid-phase extraction has unparalleled advantages, as follows:

Purification method: LLE (liquid-liquid extraction)

Advantages: no special equipment required

Cons:

1. Cumbersome and time-consuming operation

2. Need to consume a large amount of organic solvents, resulting in high costs and environmental pollution

3. Difficult to extract highly water-soluble substances from water

Purification method: PPT (protein precipitation)

Advantages: simple operation, no special equipment required

Cons:

1. Non-specific precipitation reactions may cause trace analytes to be lost with co-precipitation of matrix proteins.

2. Weak purification effect, low detection sensitivity and reliability.

SPE (Solid Phase Extraction)

advantage:

1 Can complete sample enrichment and purification at the same time, greatly improve detection sensitivity

2 faster than liquid-liquid extraction, more solvent-saving, can be automated batch processing

3 good reproducibility

Cons:

1. The cost of using imported SPE cartridges is higher

2. Require professional assistance for method development

1. A sample includes isolates and interfering substances through an adsorbent;

2. The adsorbent selectively retains the isolate and some interferences, and other interferences pass through the adsorbent;

3. Rinse the adsorbent with an appropriate solvent to selectively wash off previously retained interfering substances, and keep the isolate on the adsorbent bed;

4. The purified, concentrated isolate is rinsed from the adsorbent.