Introduction to Solid Phase Extraction Technology

Solid phase extraction technology

Solid Phase Extraction (SPE) technology was developed in the 1970s. Due to its high efficiency, reliability, and low consumption of reagents, it has replaced traditional liquid-liquid extraction in many fields and has become an effective means of sample preparation. Solid-Phase Extraction (SPE) is a sample pretreatment technology developed in recent years. It is synthesized by liquid-solid extraction and column liquid chromatography. It is mainly used for sample separation, purification, and concentration.

Conventional liquid-liquid extraction can avoid many problems, such as easy emulsification, incomplete phase separation, lower quantitative analytical recovery, expensive fragile glassware, and large amounts of organic waste. Solid phase extraction can effectively separate the target analyte from the interference component, which can improve the purity and recovery rate of the target analyte, reduce the relative deviation, improve reproducibility, and facilitate more accurate qualitative and quantitative analysis of the target analyte.

Some of the traditional books on SPE attribute it to the principle of liquid chromatography, which is actually one of the main sources of improper use. Think of the SPE cartridge as a liquid chromatography column. It is better to think of it as a simple extractant because the focus of liquid chromatography is on separation, while the focus of SPE is on extraction. The role of solid phase extraction in sample processing is divided into two types, purification, and enrichment. These two effects may exist simultaneously.
Solid phase extraction technology
SPE technology is a column chromatography separation process. The technology is an integration of liquid-solid extraction and column liquid chromatography. The combination of this technology gets over the disadvantage of the low recovery rate of the analyses by the traditional liquid-liquid extraction method.

Solid phase extraction technology can conveniently process multiple samples at the same time, greatly reducing the workload and operation time of sample pretreatment, and effectively improving work efficiency. Improves the recovery efficiency, makes the separation between the interferer and the analyses more effective, reduces the sample pretreatment process, and is simple to operate, time-saving and labor-saving.

As a fast and efficient sample preparation technique for cleanup and concentration for analysis of HPLC, GC, TLC, UV, IR, Solid Phase Extraction, as we called “SPE”, is also an excellent tool used by most chromatography in the lab nowadays.

SPE is well designed to extract, partition, and adsorb one or more components from a liquid phase onto a stationary phase. The principle can be described as that: by an increase in the elution strength of the eluent, an adsorbed substance can be removed from the simple adsorbent perfectly.

Compared to classical liquid-liquid extraction, SPE has lots of Advantages: convenience, lower consumption of solvents and sample costs, high consistency of sample handling, more time savings, and specific selectivity. The shortcoming is that the repeatability between batches is difficult to guarantee. The reason for this is that the reproducibility of the liquid reagent is good, and the physicochemical properties of the products of different ages are reliable as long as the purity is reliable. However, even if the solid extractant guarantees purity, there are differences in particle size, differences in shape, and other factors that are not present and difficult to measure. The extraction properties of different batches may be different in different years. SPE is put into practice by more and more scientists because it can not only extend a chromatographic system’s operation life but lessen the demand for analytical instruments.

Theoretically and by manufacturers, solid phase extraction should be well applied in the pretreatment of chromatographic analysis: organic solvents are used very little, and samples can be processed in batches, which can be enriched and decontaminated. The impression is a revolutionary advancement in pre-processing. However, the reality is at least in China. Although it has been promoted for many years, the practical application is quite limited.

Solid phase extraction can be a good supplement to the pretreatment method, but when using it, be sure to know its advantages and disadvantages, pay attention to local conditions, and avoid weaknesses.

In recent years, a large number of national and industry standards for the application of solid-phase extraction technology have been promulgated. And widely used in food safety testing, agricultural product residue monitoring, medical and health, environmental protection, commodity inspection, chemical production, and other fields.

Types of SPE Separation

SPE is typically used for the preparation of liquid samples and for the extraction of difficult or non-volatile samples, as well as for pre-extracting solid samples into solution.
How is the compound adsorbed and retained on the SPE filler?

Reverse phase solid phase extraction (polar liquid phase, non-polar solid phase)

The basic principle of antiphase bonded silica gel is nonpolar interaction. Since the silica gel is only the main body, there is a small part of the presence of silicone methanol, so there are some polar second-order interactions.
Hydrophobic interaction
1. Non-polar-nonpolar interaction
2. Van der Waals force or dispersion force

Normal phase solid phase extraction (non-polar liquid phase, polar solid phase)

Hydrophilic interaction
1. Polarity – Polar interaction
2. Hydrogen bond
3. π – π interaction
4. Dipole-dipole interaction
5. Dipole-induced dipole interaction

Ion exchange extraction

How ion-exchange solid phase extraction preserves a compound depends largely on the pH of the sample and the pretreatment solution. In order to preserve the compound, the pH of the sample should ensure that the functional groups on the analyte and on the silica surface are negatively charged.
1. Charged compounds are electrostatically attracted to the surface of the charged adsorbent
2. Adsorption (the role of compounds and adsorbent materials)
3. Hydrophobic interactions or hydrophilic interactions, depending on the solid phase material you choose.

Hawach offers you a wide range of chemistries, adsorbent types, and sizes, and it is important to choose the right product for your needs and sample properties.

Being used in sample separation and pretreatment, Hawach SPE Cartridges are divided into silica gel, polymer, adsorption type, the special cartridge according to matrix type. The cartridge has three parts: a medical PP empty tube, a medical PE sieve plate, and a fixed adsorbent.

The application advantages of solid phase extraction

In the pre-treatment of any project, it is suitable to use solid phase extraction technology, that is, solid phase extraction is more ideal than ordinary solvent extraction.

1. Pretreatment of organic matter in water.

Such conventional treatment is basically oscillating extraction with an organic solvent which is incompatible with water, and the advantage of solid phase extraction is that

a. Pre-processing can be repeated quantitatively.

Solvent oscillation operation generally only requires the degree of control time, but can not control the oscillation frequency, intensity, and action. We know that each person’s oscillation action is different, that is, the same person, it is difficult to ensure that the action is always uniform. Therefore, the action of solvent extraction is not quantitative and cannot be repeated.

In the case of solid phase extraction, it is easier to maintain the uniformity and stability of the column and the elution rate. Therefore, the extraction process of the solid phase extraction can be repeated and quantifiable.

b. On-site processing.

The analysis of organic matter in water has a bottleneck that has long plagued us. That is to say, organic matter can remain relatively stable in ponds and reservoirs, etc., but once it enters the small environment of the sampling bottle, it will change rapidly. Therefore, many water organic matter analysis methods require immediate analysis, and the maximum can not exceed 4 hours. The general situation is that the time from the water withdrawal to the laboratory is far more than 4 hours, the sample has changed, and the reliability of the analysis results can be imagined.

If the solid phase extraction technology is introduced, since it is simple in equipment, small in size, and easy to carry, it can be sampled at the site and pretreated. The sampler brought back to the lab was a solid phase extraction column instead of a water sample. This will ensure that we are dealing with water samples that are truly stable.

From practical applications, the use of solid phase extraction technology to replace traditional liquid-liquid extraction in the detection of water still has considerable work to be explored. It is not completely replaced at present, but its development prospects are worthy of optimism.

c. Reduction in the consumption of organic reagents.

When using a solid phase extraction, it is only necessary to use an organic solvent at the time of elution, which is a little more than ten times that of conventional liquid-liquid extraction. It has a positive significance for the personal protection and environmental protection of the experimenter.

2. Pharmaceutical ingredient extraction of bulk biomaterials

This is an example of the success of solid phase extraction in practical applications. It mainly refers to the pretreatment work when testing blood samples and urine samples in hospitals. Because the adsorption of drug components is the advantage of solid phase extraction, plus the sample is single, and the composition is fixed, it is very suitable for large-scale batch purification operation after determining the method.

3. Immunoaffinity solid phase extraction.

The ideal state of extraction is specific enrichment or specific repellent, but whether it is solvent extraction or solid phase extraction, it is basically similarly soluble, and at most, it can achieve “a certain type of level” of extraction, but cannot reach “some A “level of extraction.

Adding immunoaffinity technology to the solid phase extraction column can make use of its biospecific selective adsorption to achieve a near-theoretical perfect extraction.

The practical difficulty is that although the concept is very good, it is less available due to the relatively high technical difficulty.