What are the general natural product extraction methods? How to remove residual substances

1. The principle of solvent extraction method: solvent extraction method is based on the solubility of various components of Chinese herbal medicine in the solvent, the choice of the active ingredient solubility, the solubility of the components do not need to dissolve the solvent small, and the active ingredient dissolved out of the herb tissue method. When the solvent is added to the raw materials of Chinese herbal medicine (need to be crushed properly), the solvent due to diffusion, osmosis gradually through the cell wall into the cell, dissolved soluble substances, resulting in the concentration difference between inside and outside of the cell, so the concentrated solution inside the cell continues to diffuse outward, the solvent continues to enter the cells of the medicinal herb tissue, and so on many times back and forth until the concentration of the solution inside and outside of the cell reaches a dynamic equilibrium, the saturated solution will be filtered out!

2. Solvent selection: the key to the use of solvent extraction method is to select the appropriate solvent. Proper selection of solvents, you can more smoothly extract the required components. Selection of solvents should pay attention to the following three points: ① solvent solubility of active ingredients, impurities solubility is small; ② solvent can not be chemical changes with the composition of Chinese medicine; ③ solvent should be economic, easy to obtain, safe to use.

3. Extraction method: solvent extraction of herbal components, commonly used impregnation, percolation, decoction, reflux extraction and continuous reflux extraction method. At the same time, the crushing of raw materials, extraction time, extraction temperature, equipment conditions and other factors can also affect the extraction efficiency, must be considered.

1) impregnation method: impregnation method will be powdered or crushed Chinese herbal medicine in a suitable container, add suitable solvents (such as ethanol, dilute alcohol or water), impregnation of herbs in order to dissolve the components of the method. This method is relatively simple and easy to implement, but the leaching rate is poor, and such as water as a solvent, the extract is easy to mold and deterioration) must pay attention to adding appropriate preservatives.

2) percolation method: percolation method is the powdered herbs in the percolator, constantly adding new solvents, so that it penetrates through the herbs, from top to bottom from the lower part of the percolator out of the leaching solution of a leaching method when the solvent penetrates into the powdered dissolved components of the specific gravity of the increase and move down, the upper layer of the solution or dilute leaching solution will replace its position, resulting in a good difference in concentration, so that the diffusion can be carried out better, so leaching! The effect is better than the impregnation method. However, the flow rate should be controlled, in the process of seepage at any time from the surface of the drug to replenish the new solvent, so that the active ingredients in the herbs fully leached until. Or when the color of the seepage droplet is very light or the volume of the seepage solution is equivalent to: 10 times the weight of the original herbs, it can be considered that basically has been extracted completely. In mass production will often collect the dilute ooze as a solvent for another batch of new raw materials.

3) decoction method: decoction method is the earliest use of China's traditional leaching method. The containers used are generally pottery, sand pots or copper, enamelware, should not use iron pots, so as to avoid discoloration of the liquid. It is best to stir from time to time when heated by direct fire, so as not to localize the herbs are heated too high and easily scorched. Pharmaceutical factories with steam heating equipment, mostly use large reaction pots, large copper pots, large wooden barrels, or cement-built pools passed into the steam heating. Several decoctors can also be connected to each other through pipes for continuous decoction and immersion.

4) reflux extraction method: the application of organic solvents heated extraction, the need to use reflux heating device, so as to avoid loss of solvent volatilization. When operating in small quantities, a reflux condenser can be connected to a round-bottomed flask. Bottle loaded with herbs about the capacity of % ~ %, solvent immersion over the surface of the herbs about 1 ~ 2cm. heating reflux in a water bath, generally keep boiling for about 1 hour of small cooling filter, and then in the dregs of the solvent, for the second and third heating reflux were about half an hour, or to the basic mention of the active ingredient until exhaustion. This method of extraction efficiency is higher than the cold immersion method, a large number of production in the continuous extraction method.

5) dynamic continuous extraction method: the application of volatile organic solvents to extract the active ingredients of Chinese herbal medicine, regardless of small-scale experiments or large-scale production, are good to continuous extraction method, and the amount of solvents required is less, and the extracted components are more complete. Laboratory commonly used fat extractor or Soxhlet extractor. Continuous extraction method, it generally takes several hours to extract completely. Extracted components are subjected to heat for a long time, the heat is not stable and easy to change the composition should not use this method.

6) water vapor distillation: water vapor distillation method, applicable to the extraction of herbal ingredients that can be distilled with water vapor without being destroyed. Such components of the boiling point of more than 100 ℃, and water is not miscible or only slightly soluble, and at about 100 ℃ when the existence of a certain vapor pressure. When heated with water, its vapor pressure and water vapor pressure sum for an atmosphere, the liquid begins to boil, the water vapor will be volatile substances are brought out. Examples include the volatile oils in Chinese herbs, certain small molecule alkaloids such as ephedrine, schoenanthine, betulinine, and certain small molecule phenolic substances. Peony phenol (paeonol), etc., can be applied to this method of extraction. Some volatile components in water solubility is slightly larger, often the distillate re-distillation, in the first part of the distillation, divided into volatile oil layer, or in the water layer of the distillate by salting out the method and with a low-boiling solvent will be extracted out of the ingredients. For example, rose oil, protoanemonin (protoanemonin) and other preparations are mostly used in this method.

7) sublimation method: solid substances directly vaporized by heat, and solidified into solid compounds when cold, known as sublimation. There are some ingredients in Chinese herbal medicine has the nature of sublimation, so you can use the sublimation method directly from the extraction of Chinese herbal medicine. For example, camphor sublimation of camphor (camphor), in the "Compendium of Materia Medica" has been recorded in detail, for the world's first application of sublimation method to obtain the active ingredient of medicinal herbs account. The caffeine in tea can be sublimated above 178℃ without being decomposed. Free hydroxy anthraquinone components, some coumarins, organic acids, some also have the nature of sublimation. For example, heptaphyllum lactone and benzoic acid. Sublimation method, although simple and easy to implement, but after the charring of herbs, often produce volatile tar-like, adhering to the sublimation material, not easy to remove by refining, and secondly, sublimation is incomplete, low yield, sometimes accompanied by decomposition phenomenon.

4. Separation and purification:

(a) solvent separation method: generally the above total extract, the choice of three or four different polarity solvents, from low polarity to high polarity step by step extraction and separation. Water or ethanol extract is often a gum ambrosia, it is difficult to uniformly dispersed in low-polarity solvents, so it can not be extracted completely, can be mixed with an appropriate amount of inert filler, such as diatomaceous earth or fiber powder, and then low-temperature or natural drying, crushing, and then selected solvents in order to extract, so that the total extract of the constituent components, according to their solubility in different polar solvents and get separated. For example, powdered anthemis ethanol extract, alkalization can use ether to dissolve fat-soluble alkaloids, and then cold benzene treatment to dissolve powdered anthemis alkaloids, and its structure is similar to anthemis norelin alkaloids than the former less than a methyl group and a phenolic hydroxyl group, insoluble in cold benzene and can be separated. Using the chemical composition of Chinese herbal medicine, solubility in different polar solvents for separation and purification, is the most commonly used method.

(B) two-phase solvent extraction:

1. Extraction: two-phase solvent extraction is also referred to as extraction, is the use of the components of the mixture in the two immiscible solvents in the distribution coefficients of the difference between the methods to achieve separation. Extraction if the components of the two-phase solvent distribution coefficient of the greater the difference, the higher the separation efficiency, if the active ingredient in the aqueous extract is lipophilic substances, generally more lipophilic organic solvents, such as benzene, chloroform, or ether two-phase extraction, if the active ingredient is biased hydrophilic substances, in the lipophilic solvents are difficult to dissolve, you need to change to a weakly lipophilic solvent, such as ethyl acetate, butanol, and so on. It is also possible to add appropriate amounts of ethanol or methanol to chloroform, ether to increase its hydrophilicity. Extraction of flavonoids, more two-phase extraction with ethyl acetate and water. Extraction of hydrophilic saponins are mostly used n-butanol, isoamyl alcohol and water for two-phase extraction. However, the greater the general hydrophilicity of organic solvents, and water for two-phase extraction of the effect is worse, because it can make more hydrophilic impurities accompanied by the further refinement of the active ingredient has a great impact.

2. Countercurrent continuous extraction: a continuous two-phase solvent extraction. The device can have a, several or more extraction tube. Tube filled with a small ceramic ring or small stainless steel wire ring to increase the contact surface of the two-phase solvent extraction. For example, chloroform is used to extract neemin from an aqueous extract of neem bark. Chloroform in the extraction tube, and the specific gravity is smaller than the chloroform water extract concentrate stored in the high level container, open the piston, then the water leachate in the high level of pressure flow into the extraction tube, meet the ceramic ring impact and dispersed into fine particles, so that the contact surface with the chloroform increased, the extraction will be more complete. If a herbal infusion needs to be lighter than water, benzene, ethyl acetate, etc. for extraction, the water extract concentrate should be installed in the extraction tube, and benzene, ethyl acetate stored in a high level container. Whether the extraction is complete, the sample can be taken with thin layer chromatography, paper chromatography and color reaction or precipitation reaction to check.

3. Countercurrent distribution (CounterCurrentDistribution, CCD): Countercurrent distribution method, also known as countercurrent solubilization, countercurrent distribution method or countercurrent distribution method. Countercurrent distribution method and two-phase solvent countercurrent extraction principle is the same, but the amount of samples must be added, and constantly in a certain capacity of the two-phase solvent, after a number of shifts in the extraction and distribution to achieve the separation of the mixture. The countercurrent distribution instrument used in this method is composed of several or even hundreds of tubes. If this instrument is not available, a dispensing funnel can be used instead for small extractions. Pre-select two immiscible solvents that are more effective for the separation of mixtures, i.e., that have a large difference in partition coefficients. Referring to the behavioral analysis of partition chromatography to deduce and select the solvent system, and through the test to measure how many times the extraction shift to achieve a true separation. Countercurrent partitioning can often give good results in separating mixtures with very similar properties. However, the operation time is long, the extraction tube is easy to be damaged by mechanical oscillation, the consumption of solvent is also more, the application is often subject to certain limitations.

4. Droplet countercurrent distribution method: droplet countercurrent distribution method, also known as droplet countercurrent stratification. In recent years, the two-phase solvent extraction method has been improved on the basis of the countercurrent distribution method. The choice of solvent system is basically the same as the countercurrent distribution method, but requires a short period of time to separate into two phases, and can generate effective droplets. Due to the mobile phase droplet formation, in the fine distribution extraction tube with the fixed phase effective contact, friction constantly forming new surfaces, to promote the distribution of solutes in the two-phase solvent, so its separation effect is often better than the countercurrent distribution method. And does not produce emulsification, with nitrogen pressure driven mobile phase, the separated substances will not be oxidized due to oxygen in the atmosphere. This method must use a solvent system that can generate droplets, and the separation of polymer compounds is less effective, small sample size (less than 1 gram), and certain equipment. The application of droplet countercurrent distribution method has been effective in the separation of a variety of trace components such as Chaihu saponin original berberine-type quaternary ammonium base. Droplet countercurrent distribution method of the device, in recent years, although constantly improving, but the device and operation is more complicated. At present, the separation of components suitable for countercurrent partitioning method, two-phase solvent countercurrent continuous extraction device or distribution column chromatography can be used.

(C) precipitation method: it is the method of adding certain reagents to the herbal extract to produce precipitation and remove impurities.

1. Lead salt precipitation: lead salt precipitation is one of the classical methods for separating certain herbal components. As lead acetate and alkaline lead acetate in water and alcohol solution, can be generated with a variety of herbal ingredients insoluble lead salt or complex salt precipitation, so this property can be utilized to make the active ingredient and impurity separation. Neutral lead acetate can be combined with acidic substances or certain phenolic substances to form insoluble lead salts. Therefore, commonly used to precipitate organic acids, amino acids, proteins, mucus, tannins, resins, acidic saponins, some flavonoids. A wider range of insoluble lead salts or complexes can be produced with alkaline lead acetate. Usually the water or alcohol extract of Chinese herbal medicine is first added to a concentrated solution of lead acetate, after standing, the precipitate is filtered out, and the precipitation wash is incorporated into the filtrate, and the saturated solution of alkaline lead acetate is added to the filtrate until no precipitation occurs, so that the three parts of lead acetate precipitates, alkaline lead acetate precipitates, and the mother liquor are obtained.

The lead salt precipitate is then suspended in a new solvent, and hydrogen sulfide gas is passed through it to make it decompose and turn into insoluble lead sulfide and precipitate. The mother liquor containing lead salts must also be deleaded in the same way first, and then concentrated and refined. Hydrogen sulfide is more complete, but there may be excess hydrogen sulfide in the solution, so air or carbon dioxide must be passed through to let the gas bubbles carry out the excess hydrogen sulfide gas, so as not to participate in the chemical reaction when treating the solution. New ecological lead sulfide is mostly colloidal precipitation, can absorb the active ingredients in the solution, be careful to use solvents to deal with the recovery