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one. Introduction to 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 into samples in many fields. An effective means of pre-processing.
Some of the traditional books on SPE attribute it to the principle of a 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: one is purification, and the other is enrichment. These two effects may exist simultaneously.
Compared with liquid-liquid extraction, the advantages of solid extraction are that it is convenient and consumes less reagents. 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 the 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.
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. 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.
SPE is not widely used, it is related to our usage and expectations, and it is also related to its own limitations. For suppliers, from the economic interests, the limitations and shortcomings of solid phase extraction have always been ignored. 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.
Second, the application advantages of solid phase extraction In the pre-treatment of what projects are suitable for the use of solid phase extraction technology, that is, solid phase extraction is more ideal than ordinary solvent extraction, personally believe that there are the following:
(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 (1) the pretreatment process can be quantitatively repeated.
Solvent oscillation operation generally only requires the degree of control time, but can not control the oscillation frequency, intensity, 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 solution 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.
(2) 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 zui can not exceed 4 hours. In general, the time from the water withdrawal to the laboratory is much more than four 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.
(3) 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 positive significance for the personal protection and environmental protection of the experimenter.
(II) Pharmaceutical component extraction of bulk biomaterials This is a successful example of solid phase extraction in practical applications. It mainly refers to the pretreatment work when testing blood samples and urine samples in hospitals. The adsorption of drug components is solid phase. The advantages of extraction, together with the single sample and fixed composition, are very suitable for large-scale batch purification operations after the method is determined.
(3) Immunoaffinity solid phase extraction.
The ideal state of extraction is specific enrichment or specific repellent, but whether it is solution extraction or solid phase extraction, it is basically similarly compatible, and Zui does more than “a certain class†level of extraction, but cannot achieve “ A kind of "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.
Third, the application of solid phase extraction limitations (1) sample localized solid phase extraction is not suitable for processing solid samples. For solids, it must be prepared in liquid form for solid phase extraction, which is far less than liquid extraction.
Even for liquid samples, solid phase extraction has additional stringent requirements. 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 will not 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) Structure limitation The structure of the solid phase extraction column is very simple, except for the plastic tube, only the sieve plate and the filler. With this simple structure, it brings convenience and inherent contradictions, some of the contradictions we never encounter when extracting with solvents.
Contradictions 1 liquid level problem.
When we perform typical solid phase extraction operations such as activation, purification, elution, etc., different solvents are used. At this time, the operation requires adding different solvents when the liquid level drops to the sieve plate, and adding too late will cause the filler to be in the filler. Drying produces bubbles that affect the stability of the results (even the liquid level cannot be lowered due to the tension of the solution). Conversely, if added too late, the addition of the solution and the original solution on the sieve plate will result in a new eluent that is undesirably undesirably polar, which will reduce the reliability of the results. .
Adding liquid to the sieve plate is easier said than done. If you make a sample separately, you can focus on the liquid level operation. However, in batch operation, only one thing is lost. The important significance of the 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.
The liquid level problem is the main bottleneck restricting the success of solid phase extraction applications. Although it is concealed, it cannot be avoided.
There are two ways to solve it.
* The solution is to simply ignore the trouble of the liquid surface, and do the vacuuming solution every time. This will not cause the problem of mixing the solution on the sieve plate, but there will be a new problem, that is, the filler looks It is drained, but the actual surface still has an indefinite amount of liquid. Each time the degree of dryness is inconsistent, it cannot be repeated.
Another solution is to use a conductivity probe when using a solid phase extractor. This method is more accurate, but there is a new problem. The probe needs a cleaning process, otherwise there will be cross contamination, and there are such The price of a solid phase extractor of 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.
When extracting with liquids, we never have to consider whether the density of the entire solvent is uniform, but for solid fillers, we cannot ignore this problem. In the same batch or even several small columns in the same bag, plus the same solution, we will find that the speed of the liquid through the column is not uniform, always fast and slow.
Due to the comprehensive consideration of the production process and cost, it is impossible to use a homogenization high pressure method similar to the liquid chromatography column for the solid phase extraction cartridge, so the packing unevenness of the filler is inevitable. This poses a problem. Because the speed at which the liquid flows is different, the time of each addition is different, which is not conducive to the simultaneous batch processing 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" thinking.
Contradiction 3 The quality of the filler is stable. When we open a bottle of methylene chloride or acetone, as long as it is not a counterfeit product, it can be used by different companies because their extraction performance is stable and reliable. The solid phase extraction is different, which is the genuine filler of the same company. The nature of the product is slightly different each time, and the difference between different companies is even greater. If you change a company's solid phase extraction column or a small batch of different columns in the same company, we 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. The general heating behavior can improve the adsorption. However, since the casing of the solid phase extraction column is made of plastic, it will be deformed when heated, so it can only be operated at room temperature.
(3) Project limitations According to the information provided by various suppliers, the better application is mainly in the treatment of drugs, that is, those substances with relatively large molecular weight and relatively stable nature. The similar compatibility theory of liquid extraction has been tested, and solid phase extraction relies on adsorption and elution. It is not a classical extraction process at all, and 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 we face when using solid phase extraction is: at what rate the liquid should flow out of the column. My experience is that if the effect is good, it should be slow and slow.
For the filler in the solid phase extraction column, if we look at it in a magnified view, we can see that they have a lot of voids. 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 filled with fillers. The effect is lost locally from the channel; so be slow and give them a chance to make a full effect.
How slow? One trick is not to use the so-called solid phase extractor used with the air extractor, but to use the usual gravity method. The action of gravity causes the liquid to flow downward. In terms of experimental speed, the gravity method is far less than the suction method, but in terms of experimental results, the gravity method is far superior to the suction method. The suction method can only obtain the band adsorption, but the gravity method can get the column head adsorption, in the speed and effect. In the balance of the people, we still tend to give priority to ensuring good results.
For example, a 3ml 500mg C18 cartridge, if activated with methanol, the total flow of methanol to the sieve plate is about 20 minutes, and when the sample liquid is passed, 25ml of liquid zui can flow for 2 hours, and gravity is used. If the law is right, the work rate is not necessarily much worse than the suction method. Because we 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, a stacking joint and an extension pipe can be connected. 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 the selection of solid phase extraction conditions, in order to improve the extraction efficiency, as much as possible to add liquid, or choose a small column with a large amount of filler, I think it 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 the liquid flow rate will be slower, and the diffusion during elution will be obvious.
Therefore, it is recommended that it is sufficient. When the efficiency can be ensured, the filler should be as little as possible, and the addition of liquid should not be much.
3. The experimental conditions should not be excessively refined.
Solid phase extraction is chromatographic separation in principle, but it is only used as an adsorbent extractant during operation. Due to the nature of the filler and the tightness of the packing, it is not necessary to design the effect in the actual experiment. Very complicated elution procedure.
In the establishment of conditions, we should make full use of the ready-made materials, establish the system as soon as possible, and at the same time be vigilant to the steps that are too complicated to operate, and achieve a balance between the experimental results, the experimental rate and the ease of operation.
4. Use only one solid phase extraction column and use it once. Because in a strict sense, the adsorption of many substances is irreversible, one adsorption, can not be eluted, affecting the next adsorption, although some people have done repeated experiments, but in general, in order to save a little money, greatly increased The unreliability and uncertainty of the results are very uneconomical behaviors.
Therefore it is recommended to use it only once. If you want to save money, you can start with stacking joints and extension tubes by reducing the amount of filler and using small volume tubes.
5. Careful use of solid phase extractors All suppliers will recommend solid phase extraction columns while recommending solid phase extraction columns. The simple solid phase extractor is also several thousand. If the price of an imported trademark is more than several times, Such prices do not include air compressors. However, such a configuration is coupled with a speed switch, and it is difficult to obtain 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.
As for the automatic solid phase extractor, it should be said that there is no ideal machine for food testing on the market. The main problem is that it cannot solve the problem of inconsistent liquid level drop in a small column, and the price is very expensive, and the price is also good. Naturally 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.
The current automatic solid phase extractor is basically a gravity-traffic route, but it avoids the problem of sealing.
6. Traditional liquid extraction cannot be ignored.
Some people think that it can replace liquid extraction when they first come into contact with solid phase extraction. In fact, capillary electrophoresis cannot replace liquid chromatography. Solid phase extraction is more suitable than liquid extraction in some cases, but in many cases, traditional liquid extraction is more reliable and suitable. This can be confirmed from the actual development of current experimental techniques.
Regarding liquid-solid extraction, we should not just regard it as an extraction process. From another point of view, it is still a purification process, which is a process of eliminating solid interferences. Understanding this helps us optimize the choice of experimental methods.
7. Practicality is the success of the experimental design. When designing an experiment, it is necessary to consider whether it is technically advanced. In practical use, Zui finally decides whether this method is feasible or not. The key to whether it can exist 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.
Therefore, advanced technology must also be subject to practicality, otherwise there will be no vitality.
Fives. For example, the 2003 version of the new national standard solid phase extraction technology.
In the chromatographic experiment part of the 2003 edition of the "Physical and Chemical Testing Method for Food Hygiene", compared to the 1996 version, it introduced some new technologies, mainly using the instrument method. Although the progress is obvious, there are still many mistakes, and some are even the same. In particular, some newly introduced national standards can only make people feel the tolerance and courage of the standard approval body.
Although solid phase extraction technology has been widely introduced in the 2003 edition of the national standard, its practicality is rather low if the method in the book is applied directly. The following is an example of the use of Floris silica, which is commonly used in the pesticide testing (see Table 1), to explain the main problems and solutions of the new national standard application of solid phase extraction technology.
The treatment of Flori's silica in the new national standard is the same from the beginning to the end: "Activate at 650 ° C for 4-5 hours, use 3% water to activate before use. Take a glass chromatography tube, up and down 1.5 cm high anhydrous sodium sulfate, 10 g of treated Florisil was added in the middle, and the Zui was followed by a step of rinsing and concentrating.
The above steps seem clear, but the operability is very poor, specifically analyzed into the following aspects.
(1) "Activate at 650 ° C for 4-5 hours". Although the high-temperature activation process is 5 hours, it takes more than 10 hours for the muffle furnace to drop from 650 ° C to room temperature, and the activation of the light is a whole day.
(2) “Use 3% water to activate before useâ€. Since the treated Florisil is too strong to adsorb, it is necessary to add water to inactivate. The 3% concept refers to adding 3% of the weight of Flory silica, but no one can guarantee that the water added is Uniform, this is a hidden danger of parallel results.
(3) “Loading a glass chromatography tubeâ€, it should be noted that this is a work that can be done before the experiment, and the material cannot be stored and stored.
(4) "rinsing and concentration", which is the stage of poor practicality. The volume after the general rinsing is 100 ml, and the volume requirement after concentration is generally about 2 ml. This requires the use of a rotary evaporator, and we know that the rotary evaporator is very inefficient.
As can be seen from the above four points, the problem with this series of operations is that all materials must be manually assembled before the experiment, and also through a time-consuming and labor-intensive concentration process. If this is to develop a method in a research institute, or to process only one sample a day, it is barely feasible, but it is completely unrealistic for a grassroots inspection agency like ours.
To solve the above problems, the first method is to use the ready-to-use, long-term storage of commercial columns instead of manual loading columns, and secondly to avoid large-scale concentration process.
The products of the Florisian Silica column are sold by various companies. The recommended size is 3ml, 500mg. As for the brand selection, you must buy the independent packaging column of the big company. I have bought a small brand and the effect is very poor. The filler of Flory Silica is very common. The key is whether the manufacturer has undergone a strict barbecue process before manufacturing.
Due to the use of commercial columns, it is impossible to add 3% water to activate, but according to my practical experience, the sample itself can be used to activate, so this step can be removed.
As for the “rinsing and concentration†step, I suggest that it is not necessary to elute completely and then concentrate to ensure accurate values. At some point of the elution curve, the concentration of the eluted solution will be exactly the same as the actual sample concentration. It will be consistent, as long as it can control the eluent reception at a certain point, it can completely avoid the complicated concentration process, which is more important for those projects that are inherently unstable to heat.
For example, GB/T5009.146-2003 "Determination of various residues of organochlorine and pyrethroid pesticides in plant equipment" requires the addition of 2ml petroleum ether test solution to the hand-filled Flory silica column, and then 100ml. After petroleum ether + ethyl acetate (95+5), it was eluted, and after diluting, 100 ml was concentrated to 1 ml, and it was measured. By the above-mentioned elution curve, it is found that the first 2 ml of the eluent is eluted without the analyte, and the 2-3 ml is an eluent which is twice as high as the actual value, and the eluate of the 3-5 ml is eluent. It is consistent with the actual sample concentration, so you can take the 3-5ml eluent directly without the need to go through a process of fully eluting and then concentrating.
In this way, we can propose the following pre-treatment steps for organochlorine and pyrethroids in the "practical" vegetable foods:
1. Take 5.0 g of the dried sample in a 250 ml iodine measuring flask, add 50 ml of petroleum ether, and shake on a shaker for 30 minutes. (If it is a water-containing sample, first add an appropriate amount of anhydrous sodium sulfate and mix it, wait for it to be dehydrated and then treat it as above)
2. Filter with a triangular funnel and collect the filtrate (the filtrate can be slightly concentrated). Fix the vertical purification column, connect the stacking joint on the purification column, and connect the 24ml empty tube.
3. Add all the filtrate into the empty tube and pass the column.
4. After all the filtrate has flowed from the bottom end of the column, add 3 ml of petroleum ether + ethyl acetate (95+5), and the eluent is discarded. The entire column is capped to prevent evaporation.
5. After the eluent is added, add 3ml of petroleum ether + ethyl acetate (95+5) and collect the eluent at the bottom of the column.
6, injection.
Table 1 The number of pages extracted from the pesticide project part of the “Physical and Chemical Testing Methods of Food Hygiene (II)†Item Name Filler Type 47 Cypermethrin Al2O3 75 Tricyclazole Al2O3 364 Butachlor Ammoxide 341 Organophosphorus multi-component gel permeation (GPC)
347 organochlorine and pyrethroid gel penetration (GPC)
359 carbamate gel penetration (GPC)
23 chlorothalonil florin silica 29 permethrin Florisil 41 41 sulphur phosphorus Florisil 59 quetiapine Florin Silica 127 Triazolone Floris Silica 145 Fosfoss Floris Silica 155 èŽ ä½› ä½› ä½› ä½› ç¡… 161 Green Philippine Silica Silica 166 Grass Enemy Floris Silica 173 Indigenous Urea Florin Silica 179 Pentachloronitro Benzefolim Silica 217 Pivofloxacin Florin Silica 230 Methyliso-phosphorus Florin Silica 239 Organochlorine and Pyrethroid Floris Silica 247 Isolation Urea Folly Silica 297 Indigo Spirit Flori Silica 3692, 4-D Butyl Corylin Silica 420 Vlore Floris Silica 427 Thiophenone Floris Silica 431 Metoclopramide Floris Silica 4372 , 4-Drop Flori Silica 447 Enemy Floris Silica 465 Ethyl Ketone Flore Silica
(Source: Xinjiang Henglida Technology Development Co., Ltd.)
Application of Solid Phase Extraction Technology in Sample Processing
In the 2003 edition of the “Food Hygiene Testing Methodology†standard series, a major change is that many projects, especially the pretreatment of pesticide projects, generally use solid phase extraction technology (see Table 1 for details). The principle, use and misunderstanding of this technology are now discussed.