Application of Solid Phase Extraction Technology in Sample Processing

November 04, 2020

Then advanced technology, therefore. Also obey the practicality, otherwise there will be no vitality.
A major change is the many items, the 2003 version of the Food Hygiene Testing Methodology series. Especially for the pre-treatment of pesticide projects, solid phase extraction technology is commonly used. Now the principle, use and misunderstanding of this technology are discussed. .
one. Introduction to solid phase extraction technology
Developed in the 1970s, SolidPhase Extraction is referred to as SPE technology. Due to its high efficiency, reliability, and low consumption of reagents, many fields have replaced conservative liquid-liquid extraction and become an effective means of sample preparation.
This is actually one of the main sources of improper use. Think of the SPE cartridge as a liquid chromatography column. Some traditional introductions to SPE books attribute it to the principle of a liquid chromatography. 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 second is enrichment. The role of the solid phase extraction device in sample disposal is divided into two types: one is purification. These two effects may exist simultaneously
Its strength lies in the convenience and consumption of less reagents, compared to solid extraction and liquid-liquid extraction. 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, as long as the purity is reliable, the physicochemical properties of the products of different ages are reliable, and the solid extractant guarantees the purity, and there is also a difference in the granularity. The difference in shape and other liquid reagents are not present and difficult to measure. The extraction properties of different batches may vary greatly in different years.
Solid phase extraction should be well applied in the pretreatment of chromatographic analysis: organic solvents are used very little, theoretically and by manufacturers. The sample can be processed in batches, which can be both enriched and decontaminated, giving the impression of a revolutionary advancement in pretreatment. However, the reality is at least in China. Although it has been promoted for many years, the practical application is quite limited.
Related to my approach and expectations, SPE is not widely used. It is also related to its own limitations. For suppliers, starting from economic interests has always neglected the limitations and shortcomings of solid phase extraction. Solid phase extraction can be a good supplement to the pretreatment method, but when using it, be sure to know the advantages and disadvantages, pay attention to local conditions, and avoid weaknesses.
Second, the application advantages of solid phase extraction
That is, solid phase extraction is more desirable than ordinary solvent extraction, and pre-treatment of any project is suitable for solid phase extraction. Personally think that there are several situations:
a) Pretreatment of organic matter in water.
The advantage of solid phase extraction is that such conventional treatments are essentially oscillating extractions with an organic solvent that is immiscible with water.
1 The pretreatment process can be repeated quantitatively.
However, the oscillation frequency cannot be controlled, and the operation of the solvent oscillation generally only requires the level of the control time. Strength, action, know, each person's oscillating action is different from the same person, and it is difficult to guarantee a consistent action. Therefore, the action of solution extraction is not quantitative and cannot be repeated.
It is easier to adhere to the uniformity and stability of the column and elution rate, while applying solid phase extraction. Therefore, the extraction process of solid phase extraction is reproducible and quantifiable.
2 on-site disposal.
But once in the small environment of the sampling bottle, the analysis of organic matter in the water has long been a bottleneck for me. That is to say, organic matter can be relatively stable in environments such as ponds and reservoirs. It will change rapidly, so many water organic matter analysis methods require immediate analysis, and the zui can't exceed 4 hours. In general, the time from the water withdrawal to the laboratory is far more than 4 hours. Changes, the reliability of the analysis results can be imagined.
Due to its simple equipment, if solid phase extraction technology is introduced. It is small in size and easy to carry. It can be sampled on site and pre-processed. The sampler brings back the solid phase extraction column of the laboratory instead of the water sample. This will ensure that the real ingredients I have handled are stable.
In the detection of water, the use of solid phase extraction technology to replace the radical liquid-liquid extraction has considerable work to be explored, from practical applications. It is not completely replaced at present, but its development prospects are worthy of optimism.
3 reduction in the consumption of organic reagents.
If using solid phase extraction, when handling water samples. It is only necessary to use an organic solvent at the time of elution, which is a dozen times more than that of the radical liquid extraction. It has positive significance for the personal maintenance and environmental maintenance of the experimenter.
b) Pharmaceutical ingredient extraction of bulk biomaterials
Mainly refers to the pre-treatment work when testing blood samples and urine samples in hospitals. This is an example of the success of solid phase extraction in practical applications. Since the adsorption of the drug component is the advantage of solid phase extraction, and the sample is single and the composition is fixed, the method is very suitable for large-scale batch purification operation.
c) Immunoaffinity solid phase extraction.
However, whether it is solution extraction or solid phase extraction, the ideal state of extraction is specific enrichment or specific rejection. Basically, the similarly compatible Zui does a certain kind of "level extraction", but cannot achieve a certain level of extraction.
The bio-specific selective adsorption can be utilized, and the solid phase extraction column is based on the addition of immunoaffinity techniques. Achieving a perfect extraction close to theory.
However, due to the relatively high technical difficulty, the practical difficulty is that although the concept is very good. Fewer applications are available.
Third, the application of solid phase extraction limitations
1 sample limitations
It must be prepared as a liquid form for solid phase extraction, and solid phase extraction is not suitable for disposal of solid samples. For solids. This is far less than liquid extraction.
Solid phase extraction also has additional stringent requirements, even for liquid samples. That is, the liquid must be clean and free of suspended solids or other solid particles, otherwise it will form a blockage in front of the column and cannot continue to pass through the column and elute. Therefore, the solid sample is prepared into a liquid, and the liquid sample is filtered. In contrast, solvent extraction does not have this trouble, and a little dirty has little effect.
2 structural limitations
In addition to plastic tubes, the structure of the solid phase extraction column is simple. Only the sieve plate and the filler have a simple structure, which brings convenience and inherent contradiction. Some of the solvents I use will never encounter contradictions.
Contradictions 1 liquid level problem.
When performing typical solid phase extraction operations such as elution, when I perform activation and purification. Different solvents will be used. At this time, the operation requires different solvents to be added when the liquid level drops to the sieve plate. If it is added too late, bubbles will appear in the dryness of the filler, which will affect the stability of the result (even due to the tension of the solution). Conversely, if it is added too late, it will mix the solution and the original solution on the sieve plate, and a new eluent which is not expected to have unpredictable polarity will occur, which will make the result reliable. Sexually discounted.
It is easier said than done, adding liquid to the sieve. If you do a separate sample, you can focus on the liquid level operation. However, in batch operation, only one thing is lost. The practical significance of solid phase extraction technology is that it can process samples in batches conveniently and reliably. If this meaning is weakened, its practicality is greatly reduced.
Although hidden, it cannot be avoided. The liquid level problem is the main bottleneck restricting the success of solid phase extraction applications.
There are two ways to solve it.
Every time you do the pumping solution, * The solution is to ignore the trouble of the liquid surface. This method does not cause the problem of solution mixing on the sieve plate, but there will be a new problem, that is, the filler seems to be drained, but the actual appearance still has an indefinite amount of liquid, and the level of cognac is inconsistent each time. Can't repeat.
This method is more accurate. Another solution is to use a conductivity probe when using a solid phase extractor. However, there is also a new problem. The probe requires a cleaning process, otherwise there is a possibility of cross-contamination, and the price of the solid phase extractor with such a device is generally quite expensive. And one probe can only detect one sample tube at a time, and it is difficult to monitor a small number of small columns at the same time.
Contradiction 2 Packing problem of packing.
However, for solid fillers, I have never had to consider whether the density of the entire solvent is uniform when extracting with liquid. But you can't ignore this problem. The same batch or even several small columns in the same bag, together with the same solution, will find that the speed of the liquid passing through the column is not uniform, always fast and slow.
It is impossible to use a homogenization high pressure method similar to a packed liquid chromatography column for solid phase extraction cartridges due to the comprehensive consideration of production process and cost. Therefore, the packing unevenness of the packing is inevitable, which causes a problem. Because the speed of the liquid flowing is different, the time of each liquid addition will be different, which is beneficial to the simultaneous batch disposal of the sample. And the recovery rate will be different. I have seen some companies' so-called fully automatic solid-phase extractors, the principle of which has a hypothesis that the flow rate of each small column should be the same, but unfortunately, this is really a hypothesis - "false" set.
Contradictory 3 filler quality stability problem
As long as you are not buying fake products, open a bottle of dichloromethane or acetone. It is the same company that can be used with confidence, because its extraction performance is stable and reliable, while solid phase extraction is different. It is the same filler of the same company. The nature of each product is slightly different, and the difference between different companies is even greater. And if you change a company's solid phase extraction column or a small batch of different columns in the same company, I need to do a quality assessment of all the projects, it is estimated that not many people are willing to use.
Contradiction 4 can not be heated
However, since the casing of the solid phase extraction column is deformed by heating caused by plastic, the general heating behavior can improve the adsorption. Therefore, it can only be operated at room temperature.
3 project limitations
The better-performing applications are mainly in the disposal of drugs, from the information provided by various suppliers. That is, those substances with relatively large molecular weight and relatively stable properties. The similar compatibility theory of liquid extraction has been tested, and the adsorption and elution of solid phase extraction is not a classical extraction process. Not all projects are suitable. Many classic liquid extraction experiments have not been converted to solid phase extraction until now, even if the conversion is not satisfactory.
4. Precautions when applying solid phase extraction technology.
1. Be as slow as possible.
One of the problems faced is when the liquid should flow out of the column at the rate of solid phase extraction. Experience is to be effective, slow, and slow.
If viewed in partial magnification, for the filler in the solid phase extraction column. It can be seen that it has a lot of gaps, and there are many channels for liquid circulation. If the flow is fast, a considerable proportion of the components to be tested are too late to be completely lost to the filler from the channel; so it is slow and gives it a full effect. opportunity.
And the ordinary gravity method is adopted. The action of gravity causes the liquid to flow downward. How slow is the experiment speed? One trick is not to use a so-called solid phase extractor that works with an air extractor. Gravity method is far less than suction method, but in terms of experimental effect, gravity method is far superior to suction method. With suction method, only band absorption can be obtained. Gravity method can get stigma adsorption, balance between speed and effect, or tendency Give priority to ensuring good results.
A 3ml 500mg C18 cartridge, for example. If methanol is activated, the total flow of methanol to the sieve plate is about 20 minutes, and when the sample liquid is passed, 25 ml of liquid zui can flow for 2 hours, and if it is properly used by gravity, the working rate is not necessarily worse than the suction method. a lot of. Because I can make full use of the idle time, there must be someone waiting by the suction method, and the gravity method can make full use of the lunch break and the evening time to pass the column because the electricity is not needed. When the liquid volume is large, connect the stacking joint and the extension tube. Arrange the experimental steps and work as efficiently. In addition, the gravity method does not require an aspirator and a solid phase extractor.
2. Try to be as small as possible.
In order to improve extraction efficiency, solid phase extraction conditions were selected. Add as much liquid as possible, or choose a small column with a large amount of filler, which is not necessary. Especially when using the gravity method, due to the high efficiency, in many cases the column head is adsorbed, not all the fillers are working, and the fillers are more than just the liquid flowing out at a slower rate, and the diffusion during elution is obvious.
It is enough, so it is recommended. When the efficiency can be ensured, the filler should be as small as possible, and the addition of liquid should not be much.
3. The experimental conditions should not be excessively refined.
However, in operation, Zui only uses it as an adsorbent extractant, and solid phase extraction is in principle chromatographic separation. Due to the nature of the filler and the tightness of the tightness, it is not necessary to design a complicated elution procedure in the actual experiment because of the pursuit of the effect.
It should be used as much as possible in the use of readily available materials. Establish a system as soon as possible, and at the same time, we must strike a balance between vigilance, experimental results, experimental rate and ease of operation.
4. Use only once
The adsorption of many substances is an irreversible primary adsorption, and the solid phase extraction column is only used once. Because in a strict sense. Can not be eluted, affecting the next adsorption, although some people have done repeated experiments, but in general to save a little money and greatly increase the unreliability and uncertainty of the results, it is not cost-effective.
Use it only once. If you want to save money, you can start with reducing the amount of filler and using a small volume tube, so it is recommended. Use stacking joints and extension tubes as much as possible.
5. Use a solid phase extractor with caution
Selling solid phase extractors, all suppliers are recommending solid phase extraction columns. The simple solid phase extractor of zui also has several thousand. If the price of an imported trademark is more than several times, the price does not include the aspirator. However, such a configuration is coupled with a speed switch, and it is difficult to get good results. The main problem is to enlarge the non-parallelism of the small column.
Recommendation: It is not suitable for the gravity method to use a solid phase extractor.
It should be said that as for the fully automatic solid phase extractor. There is no ideal machine for food testing on the market. The main problem is that it can't solve the problem of inconsistent liquid level drop in a small column. The price is very expensive and the price/performance ratio is not high. With liquid level measurement, it is also impossible to simultaneously detect multiple batches of small columns and there is a risk of cross contamination.
Instead, it avoids the problem of sealing. The current fully automated solid phase extractor is basically a gravity route.
6. Conservative liquid extraction cannot be ignored
It is always thought to replace liquid extraction, and some people are in contact with solid phase extraction for the first time. In fact, capillary electrophoresis cannot replace liquid chromatography. Solid phase extraction is more suitable than liquid extraction in some locations, but more often, conservative liquid extraction is more reliable and appropriate. This can be confirmed from the actual development of current experimental techniques.
Don't just think of it as an extraction process, about liquid-solid extraction. From another point of view, it is still a purification process that removes solid interferences from the purification process. Understanding this will help me optimize my choice of experimental methods.
7. Practicality is the final criterion of the experimental design victory or not
Start by considering whether it is technologically advanced. In practice, when designing an experiment. Zui finally decides whether this method is feasible or not. The key to the existence is practicality. An experimental method not only solves the problem, but also achieves balance in terms of manpower, material resources, and financial resources, and meets the requirements of sustainable and repeatable operation.
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